Agent

Human CMV is classified as a betaherpesvirus by virtue of tropism for salivary glands high species specificity (no natural host other than humans) and slow, nonlethal growth in cell culture.146 Of the human herpesviruses, CMV is most closely related genetically to HHV-6.147 CMV virions range from 150 nm to 200 nm in diameter and may be distinguished from other herpesviruses by having a more pleomorphic envelope.148 CMV has the largest genome of all herpesviruses at 230 kbp, with a large-scale...

Epidemiology Incidence

V. parahaemolyticus is the most commonly isolated noncholera vibrio. In Japan, it has traditionally been implicated as the cause of at least one-fourth of food-borne disease cases.16 After having shown a decreasing trend in recent years, V parahaemolyticus cases started to increase again around 1994 in Japan. Between 1996 and 1998, the number of cases more than doubled, with 12,346 cases in 850 incidents reported in 1998 this increase appears to be linked with the appearance of the new clonal...

Diagnosis

A high index of suspicion is necessary to make the diagnosis of psittacosis. Confirmation is by serologic test the microimmunofluorescence test is more sensitive and species-specific than the complement fixation test (CF). C. psittaci may also be isolated in tissue culture, but most laboratories do not have the capability of cultivating chlamydiae. An antibody titer of 1 64 by the CF test is considered diagnostic. A fourfold rise in titer is also diagnostic. The CF test is genus-specific and...

Info

Our test will, therefore, have a sensitivity of 80 and a specificity of 90 . The actual utility of this test, however, will rest not only on its sensitivity and specificity but also on the prevalence of the disease in question in our population of interest. In our preceding example, there was a 50 prevalence of schistosomiasis (500 infected individuals who lived in a population of 1000). If we assume that the true prevalence of schistosomiasis in a different village is 20 , at a population...

Pathogenesis And Immunity

HHV-8 was first detected as a unique DNA sequence from an AIDS KS skin biopsy using PCR-based representational difference analysis.447 Subsequently, this DNA sequence was detected by PCR in nearly all lesional skin biopsies from patients with all forms of KS classic, endemic African, iatrogenic, and epidemic AIDS associated.447-451 Virus has been localized within the KS tumor cells by in situ hybridization.452,453 However, viral DNA has also been detected in other tissues as well, including...

Prevention And Control

When cases of nosocomial Legionnaires' disease are diagnosed, the potable water distribution system of the hospital should be cultured for Legionella. If legionella is found, heating the water to 160 F (70 C) for several days and then flushing hot water throughout all the outlets can result in temporary reduction of the concentration of Legionella in the water. Hyperchlorination or the addition of copper and silver ions to the water supply can also control contamination of the potable water and...

Molecular Epidemiology

Molecular biologic techniques have been applied to analyze V cholerae O1 and O139 strains in order to determine relationships and to deduce the origin or derivation of strains. The techniques include Southern blotting of restricted chromosomal DNA with specific probes, examination of restriction fragment length polymorphism (RFLP, ribotyping), pulsed-field gel electrophoresis (PFGE), multilocus enzyme electrophoresis (MEE, electropherotyping), comparison of DNA sequences, polymerase chain...

Introduction

Haemophilus influenzae is among the most common causes of bacterial meningitis and other invasive infections in infants and young children throughout the world. Historically in the developing world, it has not been recognized as a vaccine-preventable cause of serious morbidity, long-term disability, and death. The availability of an effective vaccine against H. influenzae type b (Hib), which can virtually eliminate Hib disease, underscores the importance of determining the burden of...

Stigma

The role of stigma as a major barrier to care for HIV patients has been extensively reviewed elsewhere.49-51 However, recent experiences in resource-poor settings suggest that the introduction of effective HIV treatment and care programs can help destigmatize what was once considered a fatal disease.52 In communities in rural Haiti, dramatic, visible recoveries after initiation of antiretroviral treatment, dubbed the Lazarus effect, have led to a sharp decline in HIV-related stigma.53 While the...

Treatment And Prognosis

Scrub typhus is said to respond even more promptly to antibiotics than other rickettsial diseases, with patients generally becoming afebrile within 24 to 36 hours after beginning antibiotic therapy. Early antibiotic treatment shortens the disease course, reduces mortality, and accelerates convalescence. Treatment must often be presumptive, and the benefits of avoiding severe scrub typhus by early antibiotic administration generally outweigh the risks of a 1-week course of tetracycline the...

Recurrent Salmonella Bacteremia in Individuals with AIDS

In persons with AIDS and a first episode of Salmonella bacteremia, 1 to 2 weeks of intravenous antimicrobial therapy followed by 4 weeks of oral fluoroquinolone therapy (e.g., ciprofloxacin 500 to 750 mg twice daily) should be administered to attempt eradication of the organism and to decrease the risk of recurrent bacteremia.140 Persons who relapse following 6 weeks of antimicrobial therapy should receive long-term suppressive therapy with an oral fluoroquinolone or...

Unknown Factors Limiting Distribution Absence Of Yellow Fever From Asia

In some cases, the reason for the distribution of a disease is not intuitively evident. An age-old question is, Why is there no yellow fever in Asia The answer is not known. The yellow fever forest cycle in Africa and South America involves virus, monkey, and mosquito with spillover into humans. Its urban cycle is a three-factor complex involving human beings, A. aegypti mosquitoes, and the virus. All of the nonviral factors are present in abundance in Asia, but yellow fever is absent there....

Barriers To Care And The Persistent Pathogens A Biosocial Approach

By the close of the 20th century, the world's ranking infectious pathogens from well-known malaria and filariasis to the more recently described human immunodeficiency virus (HIV) could be controlled by the tools of modern medicine and public health. And yet, none of these diseases, or other important tropical diseases, has been brought to heel. None of them, even those without a nonhuman host, have been eradicated. Some epidemic diseases continue to expand. Still others mutate to become...

Antigenic Composition and Diversity

Human strains of C. trachomatis have been classified into more than 18 serovariants (serovars) and 2 biovariants (biovars) the trachoma biovar (serovars A through K and type variants) and the LGV biovar (serovars L1 to L3).8 Infections with the trachoma biovar strains are limited to columnar mucous epithelium resulting in ocular infections, inclusion conjunctivitis, and trachoma, as well as genital tract infections. Serovars A, B, Ba, and C are typically associated with endemic trachoma,...

Disease

Tetanus is classified into four clinical subtypes generalized, localized, cephalic, and neonatal. These four clinical subtypes represent the site of toxin action, either predominantly at the neuromuscular junction or at more central inhibitory systems. Incubation time (the time from spore inoculation to first symptoms) for all clinical types seems to vary depending on the ultimate severity of the disease, with more severe disease developing more quickly (8.3 4.7 days) and mild disease taking...

Neonatal Infections

Oral erythromycin in doses of 50 mg kg body weight per day in four divided doses for 10 to 14 days is the treatment of choice for both neonatal chlamydial conjunctivitis and pneu-monia.56,57 Topical therapy for neonatal ocular infection is not recommended since it fails to eradicate chlamydial carriage in the nasopharynx, which can act as a source of infection of the lungs and reinfection of the conjunctiva. Unfortunately, ocular prophylaxis with silver nitrate, which is routinely given to...

Mark C Steinhoff Thomas Cherian

Can be biochemically typed into six biotypes (I through VI). The biotypes and the capsular serotypes are distinct typing methods, not correlated with each other. The entire Hib chromosome was sequenced in 1995, the first free-living organism to be DNA sequenced. The older H. aegyptius is found within H. influenzae biotype III and is closely related to serotype c. It was initially described by Robert Koch in Egypt in 1883 during an epidemic of conjunctivitis and subsequently isolated by Weeks....

Global Climate Change And The Spread Of Tropical Diseases

Gradual warming of the earth's surface by 1 F has been recorded during the past 100 years. This warming trend has been predicted to continue by an international panel of experts constituting the Intergovernmental Panel on Climate Change, with 2000 scientists participating.31 A few scientists still believe that the warming is a natural cycle that will reverse itself. The strongest arguments that the earth will continue to warm come from computer models of the predicted effects of accumulation of...

Principles of Microbial Evolution and Classification

The earth is approximately 4.5 to 5 billion years old. There is good fossil evidence of microbial life approximately 3.5 billion years ago. Microbial life (stromatolites) was mostly photosynthetic, unicellular, and anaerobic.1,4 Eukaryotes, bacteria, and archaea evolved from a still hypothetical universal common ancestor.5-7 Eukaryotes then evolved into protozoans, metazoans, plants, and animals, as we know them today. Moreover, there is strong evidence that primitive eukaryotic cells...

Epidemiology

More than 200 species of mammals and 150 species of fleas have been found to be naturally infected with Y. pestis. However, few of these hosts are important for maintaining enzootic or epizootic life cycles, and fewer still pose a significant risk to humans. The natural history of Y. pestis is complex, and an understanding of the organism's ecology and life cycle is helpful in defining its epidemiology and designing control and prevention strategies (Box 42-1).7-9,24-26 In its natural reservoir...

Hendra Virus Infection

The horse trainer who died of HeV infection had interstitial pneumonia. The second human who developed fatal disease died of encephalitis with histopathologic and MRI evidence of CNS lesions.10-12 In horses, the incubation period is between 8 and 11 days. An acute febrile respiratory or neurologic illness of short duration (1 to 3 days) results in death symptoms include fever, rapid and shallow breathing, congested mucous membranes, ataxia, and head pressing.2,8,10 The major pathologic changes...

Host Risk Factors

Known host factors that greatly increase the risk of developing cholera gravis include blood group O,30 hypo-chlorhydria,31,32 and a lack of background immunity.33 In both endemic and epidemic situations, persons of blood group O are clearly at much greater risk of developing cholera gravis than persons of other blood groups.30,34 When cholera invades a new, immunologically naive population, persons with hypochlorhydria (e.g., with partial gastrectomy) have often been the index case.35 In...

The Feasibility Of Other Eradication Programs

Despite the fact that, for eradication, there were many advantageous attributes intrinsic to both smallpox as a disease and to the program, the eradication effort barely succeeded. Financial support for the program was always precarious despite the fact that every country stood to gain substantially from its eradication. A number of the endemic countries themselves were reluctant participants and some were so torn by civil war that operations could be conducted only during brief intervals in...

Agent Anaplasma Phagocytophilum

A. phagocytophilum contains a number of protein antigens, and the immunodominant major surface protein-2 (Msp2) 44-kD proteins are encoded by at least 22 paralogs that appear to be individually transcribed and expressed within a single bacterial cell.19,97,98 With time, recombination by gene conversion or more complicated combinatorial mechanisms generates antigenic variants that may promote persistence in reservoir hosts by immune evasion. In hosts that develop significant clinical signs,...

Tropical Infectious Diseases

Globally, as assessed in terms of disability-adjusted life years (DALYs), which measures morbidity and mortality,111 infectious diseases in 1990 accounted for 36.4 of total DALYs. Infectious disease DALYs were considerably in excess of those attributable to cancer (5.9 ), heart disease (3.1 ), cerebrovascular disease (3.2 ), or chronic lung disease (3.5 ).116 However, these calculations admittedly miss the disproportionate impact of tropical infectious diseases on the still exploding...

Ban Mishu Allos Martin J Blaser

Species isolated.16-18 In contrast, in the United States and other developed nations, C. jejuni accounts for greater than 95 of Campylobacter species isolated.19 Other studies of Campylobacter, in Thailand,20 Hong Kong,21 and the Central African Republic,22 show a higher incidence of C. coli relative to that seen in industrialized nations. However, since methods designed to optimize detection of C. jejuni might not support growth of other species, the contribution of these organisms to the...

Association Studies

In case-control studies, people with and without a particular genotype are compared with respect to a number of variables, such as whether they are infected or not, have a higher or lower parasite load, suffer a particular form of the disease, or die or not. An early example of such a study is that of Allison,21 who determined that normal (AA) controls were more likely to have parasitemia with Plasmodium falciparum than people with sickle cell trait (AS). Unfortunately, case-control studies are...

Treatment And Control

WHO initiated a major effort to control blinding trachoma in 1997 as the Global Elimination of Blinding Trachoma by 2020 (GET 2020).2 A nongovernmental organization, the International Trachoma Initiative (ITI) was established in 2001 to distribute azithromycin donated by Pfizer Inc. for trachoma control. The ITI assists Ministries of Health in affected countries to develop systematic national trachoma control programs. In trachoma-endemic regions, the goal of trachoma intervention programs is...

Clinical Manifestations

Dictated by diverse sets of virulence determinants, the clinical manifestations of the different types of enterovirulent E. coli vary from cholera-like watery secretion with ETEC to dysentery indistinguishable from shigellosis with EIEC. The clinical characteristics of various enteric E. coli infections are summarized in Table 16-2. ETEC characteristically causes an acute watery diarrhea within 8 to 72 hours after ingestion, which ranges from a mild self-limited illness to dehydrating...

References

Everett KDE, Bush RM, Andersen AA Emended description of the order Chlamydiales, proposal of Parachlamydiaceae fam. no v. and Simkaniaceae fam. nov., each containing one monotypic genus, revised taxonomy of the family Chlamydiaceae, including a new genus and five new species, and standards for the identification of organisms. Int J Syst Bacteriol 49 415, 1999. 2. Schachter J, Stephens RS, Timms P, et al Radical changes to chlamydial taxonomy are not necessary just yet. Int J Syst Evol Microbiol...

African Tick Bite Fever

African tick bite fever (ATBF) is a milder illness than RMSF, and fatalities are rare. After an incubation period of 5 to 7 days, patients with ATBF suffer abrupt onset of fever (59 -100 ), nausea, fatigue, headache (62 -83 ), myalgia (63 -87 ), nuchal myalgia (81 ), eschars (53 -100 ), which are typically multiple (21 -54 ), regional painful lymphadenopathy (40 -100 ), rash (15 -46 ) that is either maculopapular (14 -26 ) or vesicular (0 -21 ), and aphthous stomatitis (0 -11 ).62,63 Patients...

Examples Of Specialized Surveillance And Response Networks

Global Influenza Surveillance Network Established in 1952, this global network of more than 100 virus laboratories in 83 countries monitors influenza activity and collects the viral isolates that determine the composition of the following year's influenza vaccines32 (Fig. 15-2). The isolates are characterized by WHO Collaborating Centers in the United Kingdom, Japan, Australia, and the United States. In addition to guiding the annual composition of recommended vaccines, the network operates as...

Tracking Agents With Molecular Epidemiologic Methods

In the past, our ability to determine disease distribution and movement was often hindered by inaccurate diagnosis. For instance, clinical signs and symptoms are notoriously insufficient in distinguishing causes of fever, diarrhea, or hem-orrhagic disease. The advent of reliable laboratory methods helped to confirm clinical diagnosis. In the past decade, molecular technology has matured so that not only can one map the distribution of the agent and disease but also one can determine the genetic...

Endemic Syphilis

Like yaws, endemic syphilis, previously also referred to as bejel (Arabic), is a readily transmissible disease of children.7 Although previously widespread among nomadic and semi-nomadic populations of North Africa, southwest Asia, and the eastern Mediterranean basin, endemic syphilis is now most common among nomads living in the Arabian peninsula and along the southern border of the African Sahara desert. As might be inferred by its distribution, unlike yaws, which is more common in humid...

Diseases

Folliculitis, Carbuncles, and Abscesses Abscesses can develop from skin organisms introduced into the deeper tissue, from seeding of the skin from hematogenous sources such as bacteremia associated with endocarditis, or contiguously from infectious foci in the lung or gastrointestinal tract. In the former case, hair follicles serve as a portal of entry for a number of bacterial species, though S. aureus is the most common cause of localized folliculitis. Recurrent folliculitis is most common in...

Elements Of The Immune System Nonimmune Mechanisms

Molecular genetics has made extraordinary advances in the understanding of the genetic basis and potential treatment of a large number of inherited conditions, some of whose frequency in the tropics is unknown. One such condition is cystic fibrosis caused by a mutation in the chloride transporter cystic fibrosis transmembrane conductance regulator gene (CFTR) on chromosome 7.8 The mutant CFTR with phenylalanine at position 508 resists the entry of both Pseudomonas and Salmonella typhi into...

Summary

Future challenges posed by infectious agents are difficult to predict but certainly include the continuing threat of an influenza pandemic, a recurrence of SARS, the emergence of other zoonotic agents that cross the species barrier to humans, the emergence of new bacterial strains that are more virulent or resistant to antibiotics, the possible deliberate release of pathogenic microbes by terrorists, and the likelihood of increased spread of dengue, cholera, West Nile virus, yellow fever, and...

Treatment And Prognosis Initial Therapy

In patients with mild C. difficile-associated diarrhea, cessation of the offending antimicrobial, if possible, may be all that is required. Specific therapy is indicated for patients with more severe or persistent symptoms and also for those patients who require continuation of their original antimicrobial agents (Table 23-1). Initial therapy with oral metronida-zole 250 mg four times daily, or oral vancomycin 125-mg capsules four times daily or a 500-mg intravenous preparation given orally,...

Criteria For Assessing Candidate Diseases For Eradication

Before embarking on still more eradication programs, it seems sensible to examine critically the feasibility of such efforts. Five principal determinants are proposed as minimum criteria to be met before an eradication program policy is decided. 1. There is no natural reservoir for the organism other than humans. Most infectious agents are not candidates for eradication because the responsible organism infects naturally both humans and other mammalian species or may survive naturally in the...

General Concepts

It is rare for a simple Mendelian pattern of inheritance to be apparent when considering the genetic influence on infectious disease. An exception is malaria, in which the parasite's intraerythrocytic lifestyle is influenced by a variety of both red blood cell membrane and hemoglobin variants whose inheritance is relatively simple. As a consequence, malaria has been a very fruitful model for studies of host susceptibility to infectious disease. In most infectious diseases, however, the pattern...

Boutonneuse Fever Mediterranean Spotted Fever

Boutonneuse fever differs from RMSF in a lower untreated case fatality rate (4 vs. 23 ) the presence of a tache noire (eschar) a 1-cm focus of vascular rickettsial infection and injury leading to epidermal and dermal necrosis at the site of tick bite inoculation of rickettsiae in 72 of cases and lower incidence of myalgia, petechiae, stupor, and cough.60 Illness can be severe in patients with underlying disease such as cardiac failure or diabetes, old age, alcoholism, and glucose-6-phosphate...

Basic Reproductive Rate

To convert the vectorial capacity equation into the basic reproductive rate (RO) of the particular disease, one has to include the terms that represent the life cycle of the parasite in the human host. These are represented by the number of days that the infection lasts in the vertebrate host, expressed by the disease recovery rate r (measured as the probability per day to revert to the nonparasitemic state), and by the probability c that the new secondary host will acquire the infection once...

Disease Due to M kansasii

Mycobacterium kansasii causes chronic pulmonary disease similar to reactivation TB and disseminated disease in patients with advanced AIDS. Disease due to this pathogen occurs sporadically throughout the world but is most common in the central and southwestern United States and in England and Wales. In HIV-noninfected patients with pulmonary disease, treatment with isoniazid, rifampicin, and ethambutol for 18 to 24 months or until sputum cultures have been negative for 12 months is...

Complications

Severe hypoglycemia from inadequate gluconeogenesis and exhaustion of glycogen stores is an uncommon complication seen in pediatric patients who manifest acute convulsions and even coma if serum glucose concentrations fall below 1 mmol L.43 In patients with severe dehydration and a marked decrease in renal perfusion, acute renal failure can occur. Very rarely, pulmonary edema can occur if large volumes of intravenous fluids without bicarbonate are rapidly infused in a patient with severe...

History

Three pandemics of plague have been recorded. In the Justinian pandemic (circa 542-767 ad), it is thought that plague moved from upper Egypt to the Mediterranean and spread from there to Europe and Asia Minor, ultimately causing an estimated 40 million deaths. The second plague pandemic began in Central Asia early in the 14th century, caused epidemics in China and India, and moved along caravan routes to the Near and Middle East. Entering Messina by ship in 1347, plague swept swiftly through...

Structural Barriers To Effective Aids And Tuberculosis Control

Joseph's experience is typical in many ways and instructive in most. He is one of tens of millions worldwide suffering from HIV disease and TB he lives in great poverty he sought care unsuccessfully until he simply gave up. His family did what they could to save his life, selling off meager assets and receiving contradictory advice from neighbors and from traditional healers in a country in which trained medical personnel are rare* and most care is fee-for-service. Joseph's experience is...

Epidemiology In Developing Countries

Chlamydial infections of the genital tract have a worldwide distribution and usually constitute the most common bacterial sexually transmitted infection in both industrialized and developing countries. Genital chlamydial infections share those behavioral determinants that are responsible for the spread of other sexually transmitted infections factors that are frequently more evident in many developing country settings. The ability of C. trachomatis to elicit a relatively mild inflammatory...

C2

*As noted in the text, this classification scheme is no longer used. It is included here for historical comparison. fMay not be present in all strains. *As noted in the text, this classification scheme is no longer used. It is included here for historical comparison. fMay not be present in all strains. public health measures such as sanitation, it would be very unlikely to emerge again from other S. enterica. EPIDEMIOLOGY Distribution and Incidence Patients with typhoid and paratyphoid fever...

Infectious Disease Terms

There are a number of definitions specific to the epidemi-ologic study of infectious diseases. A disease that occurs regularly in a population is said to be endemic. When a disease occurs at a frequency higher than is expected, it is said to be epidemic. A localized epidemic may be referred to as an outbreak. Diseases in animals are said to be enzootic or epizootic. After infection, there often follows a period of latency, defined as the duration of time from infection to onset of...

Constitutional Symptoms

Constitutional symptoms are a common manifestation of fever, anorexia, malaise, headache, and myalgia The first two have clear effects on the nutritional status of the host. The hallmark sign of infection, fever, is induced by the release of interleukin-1 (IL-1), IL-6, and tumor necrosis factor-a (TNF-a), which act at the level of the hypothalamus to alter the temperature set point. This host response is believed to be a favorable adaptive response, but it comes at a substantial metabolic cost....

Management of Carriers

In the absence of cholelithiasis, the majority of carriers can be cured by a prolonged course of antibiotics targeted to the susceptibility of the organism. Cure rates of approximately 80 have been reported with oral ampicillin or amoxicillin 100 mg kg day, plus probenecid 30 mg kg day taken for 3 months trimethoprim-sulfamethoxazole, one double-strength tablet twice daily, for 3 months or 750 mg of ciprofloxacin twice daily for 4 weeks.128-130 In the presence of cholelithiasis, the preceding...

Box 51 General Effects of Malnutrition on the Immune System

Decreased mucosal integrity Impeded macrophage migration Diminished T lymphocyte help in immune responses dependent on mature CD4 cells (cell-mediated immunity) Delayed kinetics and deficient antibody responses to certain antigens, particularly polysaccharide Depressed amounts of mucosal secretory IgA and specific secretory IgA antibodies in response to mucosal infections In vivo consumption of complement, depressed plasma levels of most complement components and activities effecting both...

Isolation and Identification

Freshly passed stool is preferred for the isolation of Salmonella. Stool is plated directly onto agar plates. Low-selective media, such as MacConkey agar and deoxycholate agar, and intermediate-selective media, such as Salmonella-Shigella, xylose-lysine-deoxycholate, or Hektoen agar, are widely used to screen for both Salmonella and Shigella species. New selective chromogenic media, such as CHROMagar and COMPASS agar, are more specific than other selective media, reduce the need for...

Jarisch Herxheimer Reaction

Relapsing fever is one of the few infections for which antibiotic therapy poses a significant risk of death or further morbidity, for reasons other than anaphylaxis or overdosage. Within a few hours of the first dose of an antibiotic of most any type, 80 to 90 of patients with louse-borne relapsing fever and 30 to 40 of patients with tick-borne relapsing fever experience a worsening of symptoms.77,78 In a minority of patients, the reaction is life-threatening or fatal. A mild Jarisch-Herxheimer...

Management of Lymphogranuloma Venereum

Treatment of LGV is aimed not only at curing the infection but also preventing the complications that may accompany the disease, such as scarring and disfigurement. Thus, fluctuant inguinal and femoral lymph glands should be aspirated through intact skin using a wide-bore needle to prevent the formation of inguinal or femoral ulcerations. Repeat aspirations may be required even though appropriate antimicrobial chemotherapy has been initiated. As in other chlamydial infections of the genital...

Limiting The Distribution Of Tropical Infectious Diseases By Public Health Measures

The distribution of tropical infections can be modified by public health measures. Vaccines, vector control by source reduction and pesticides, treatment, improvement of housing, and drug prophylaxis have been used to limit the distribution of tropical infectious diseases and, at least in the case of smallpox, to eradicate the disease. Several vector-borne diseases, including malaria and yellow fever, were prevalent in the American and Afro-European temperate regions during the 1700s and 1800s....

Developmental Cycle

Chlamydiae are obligate intracellular bacteria with a unique biphasic life cycle (Fig. 48-1). The cycle is initiated by the attachment of an infectious elementary body to the surface of a susceptible cell. The mechanism by which chlamydiae attach to the host cell has not been fully elucidated, though electrostatic and receptor interactions have been postulated.15,16 Once attached, the metabolically inactive elementary body (approximate size 350 nm in diameter) enters the cell by phagocytosis,...

Nucleic Acid Amplification Tests

Several nucleic acid amplification tests are commercially available for the detection of specific chlamydial nucleotide sequences which may be present in clinical specimens, including polymerase chain reaction (PCR), strand displacement assay (SDA), ligase chain reaction (LCR), and transcription-mediated amplification (TMA). In general, these assays have demonstrated extremely high sensitivities when compared to culture.47-49 The increased sensitivity is based on the theoretical ability to...

Conclusion

Vaccines already exist that protect against life-threatening infections (e.g., rabies, diphtheria), and that can eradicate major diseases (e.g., smallpox, and maybe polio), prevent diseases in susceptible populations by the immunization of surrogates (e.g., rubella immunization to prevent congenital rubella syndrome, tetanus immunization to prevent neonatal tetanus), limit morbidity (e.g., hepatitis A), and prevent late sequelae of infections (e.g., prevention of hepatitis B-associated...

Differential Diagnosis

During the first week of illness, it is difficult to clinically distinguish typhoid fever from many other febrile illnesses. Thus, the physician must suspect typhoid fever, order appropriate cultures, and consider treatment prior to obtaining bacteriologic confirmation. During the second week of febrile illness, the range of possibilities is narrowed, particularly if the other locally prevalent diseases that can cause prolonged fever are known. These include other bacterial diseases such as...

Agents

Typhus group rickettsiae have a small (1.1 X106 bp) genome a 135-kD major, immunodominant S-layer protein arranged tetragonally on the cell wall surface, peptidoglycan, and abundant lipopolysaccharide.18-22 Typhus group rickettsiae are highly adapted to the intracellular environment with its high potassium content and availability of compounds such as adenosine triphosphate (ATP), amino acids, and phospho-rylated sugars such as uridine diphosphoglucose for which the rickettsiae possess specific...

Structural Adjustment and Access to Care

The large-scale socioeconomic forces at work in the differential distribution of sickness and health often stem from decisions made far from hospital wards or even national capitals. Many African countries in fact registered improvements in health systems and indices in the years following independence. Kenya, for example, saw infant mortality decline by more than 58 between 1963 and the early 1990s.15 However, the economic crises of the 1970s and 1980s left many of these postcolonial nations...

Streptococcal Toxic Shock Syndrome

In the mid-1980s, reports of invasive GAS infections associated with bacteremia, deep soft-tissue infection, shock, and multiorgan failure began to appear in the medical literature from North America and Europe.5,20 Though all ages may be affected, the greatest increases have occurred among previously healthy persons from 15 to 50 years of age. Mortality rates of 30 to 70 have been described in patients with Strep TSS, in spite of aggressive modern treatment measures. The Strep TSS is defined...

Principles of Microbial Metabolism

Microbes are present in every ecosystem of the planet. Therefore, their metabolic pathways are as varied as their ecosystems. Based on the source of energy, they are subdivided into phototrophs (light-derived energy), lithotrophs (inorganic compound-derived energy), and heterotrophs (organic compound-derived energy). Based on the carbon source, microorganisms are either autotrophs (inorganic carbon) or heterotrophs (organic carbon).1,7 In order to obtain energy from nutrients, organisms need to...

Neonatal Chlamydial Infections

Neonatal inclusion conjunctivitis has long been recognized as the result of an infection transmitted from mothers to their babies during passage through the birth canal. With the advent of sensitive tissue culture techniques, it became apparent that some babies delivered vaginally through an infected cervix developed a mucopurulent conjunctivitis. The onset of the disease is generally insidious, following an incubation period of 1 to 3 weeks. Hyperemia, chemosis, and a discharge that becomes...

Techniques Of Genetic Dissection

It is usual to plan DNA-based dissection of the host response to infection on knowledge of the inheritance of a trait from studies of genetic epidemiology For example, the association of a particular genotype or phenotype with geographic areas that are, or have been, epidemic for a particular disease strongly suggests a genetic component. A good example is thalassemia, a condition largely found in the tropics but also in Mediterranean countries (e.g., Italy and Cyprus) that have until the...

Antigen Detection

Two antigenic targets on chlamydiae, LPS and the MOMP, have been exploited commercially in the development of non-culture diagnostic tests. Chlamydial LPS is genus-specific, and antibodies to the LPS will cross-react with all members of the family Chlamydiaceae including human and other animal pathogens.46 Enzyme immunoassay (EIA) tests and some direct fluorescent antibody (DFA) tests detect chlamydial LPS. The EIA tests are designed to detect organisms in specimens obtained from the endocervix...

Principles of Transmission

The transfer of pathogens in communities involves shedding or excretion of the infectious agent from the host and travel to and entry into a susceptible host. Some organisms are extremely sensitive to environmental conditions such as drying or exposure to sunlight and require close contact between hosts to survive transmission (e.g., Mycoplasma spp.). Others are more resistant and can travel to a susceptible host by fomites (e.g., towels, doorknobs, toys, and gloves), vehicles (e.g., food or...

Scarlet Fever

In recent years, outbreaks of scarlet fever in the United States and Great Britain have often been associated with strains of GAS-producing pyrogenic exotoxin C.16 The cases have been notably mild and the illness has been referred to as pharyngitis with rash. Historically, this form was known as benign scarlet fever, though scarlet fever has not always been a mild disease Around 1900 mortality rates of 25 were common in temperate climates on both sides of the Atlantic. Scarlet fever has been...

Q Fever in the Immunocompromised Host and During Pregnancy

Two recently recognized manifestations of Q fever include fever in immunocompromised patients and Q fever during pregnancy. The latter has been infrequently recognized but is a growing problem, especially in southern France and Israel. A recent study of 66 human immunodeficiency virus type 1 (HIV-1) seropositive persons living in Bangui, Central Africa Republic, found that 11 (16.7 ) were also seropositive for C. burnetii. Two of the seven HIV-infected patients for whom clinical data were...

The Future Of Geographic Studies

In the past decade, geographic information systems (GIS) have given new tools to the disease ecologist for studying landscape and vegetation. Remote sensing with satellite imagery (Fig. 2-2) has been used to chart surface changes in vegetation and to predict weather patterns such as El Ni o or southern oscillation through measurements of ocean surface temperature on a global basis. Predictions of cholera36 and SEPTEMBER 1997 OCTOBER 1997 NOV EM BE. F 1997 DECEMBER 1097 FIGURE 2-2 Monthly...

Transmission and Prevalence

Whereas most types of anaerobic infections are generally believed to arise from endogenous sources, C. difficile infection is usually acquired nosocomially.4 Evidence for the method of transmission of the organism is found in institutional outbreaks, in animal models of disease, and in multiple epidemi-ologic studies of C. difficile-induced colitis.4,25,27,29 The major disease-related reservoirs of C. difficile include human carriers and environmental surfaces. Clabots and colleagues31 noted a...

Innate Immunity Phagocytic Cells

Neutrophils and macrophages are the first-line generalized response to invading organisms. There is dispute about diminished neutrophil chemotaxis and adhesion in PEM,132-134 but there does appear to be a diminished bactericidal killing despite a normal generation of oxidative metabolites.133,135 Additionally, serum opsininic activity is notably depressed in patients with PEM,136 and this is likely to further diminish the microbicidal functions of neutrophils. Zinc facilitates neutrophil...

Data Expression And Analysis

When an exposure or outcome is expressed in terms of a continuous variable such as age or weight, the differences between groups may be expressed by comparing mean or median values for the two groups. Both these statistics are measures of central tendency, meaning that they describe the middle, or average, value of the data. The mean is the arithmetic average, which is simply obtained by summing the observations and dividing the sum by the number of...

Treatment of Complications

Generalized peritonitis and large quantities of pus are often found in patients with intestinal perforation, while walling off of the perforation is infrequent. If a well-trained surgeon, anesthesiologist, and operating room staff and the necessary equipment are available, operative management of typhoid perforation is indicated.79-81 If these are not available, the choice between operative and nonoperative management is controversial and must be individualized. In all cases the patient should...

Interactions at Epithelial Barrier Surfaces

The barrier functions occurring at epithelial surfaces are part of the innate host defenses and are important in determining the outcome of interactions of potential pathogens with the host. Interactions at epithelial barriers involved in defense against external microbes include not only the physical properties of the epithelial surfaces but also the overlying mucous phase, the ciliated or other propulsive activities facilitating microbe clearance, and the normal microbial flora. Vertebrate...

Effects Of Malnutrition On Infection Protein Energy

The degree to which the previous interactions occur and the extent of their actual impact gained clarity when several prospective community-based studies accurately characterized the relationship between anthropometrics and child mortality rates. By analyzing six of the most homogeneous of these studies, Pelletier et al. were able to detect a consistent relationship between the height-for-age index and the relative risk for mortality in under fives.28,29 Child mortality increased at a compound...

Climate And Disease Distribution

Climate is defined as the customary long-term (usually 30 years) pattern of the weather for any given location. Weather, on the other hand, is the short-term state of the atmosphere in regard to temperature, rainfall, humidity, and storms. Temperature is the major governing factor for the distribution of many tropical diseases. Reservoir arthropods, snails, and vertebrates have life cycles that are limited by heat and cold. Many of these creatures do not withstand freezing weather and are thus...

Treatment

Treatment of disease due to nontuberculous mycobacteria is long and difficult. Few clinical trials have been done to guide therapy. Atypical mycobacteria are usually resistant to most anti-TB drugs, although several other classes of chemothera-peutic drugs have activity against some species. The value of drug susceptibility testing in guiding treatment is controversial, and reliable testing is available only through a few specialized laboratories. Susceptibility testing is best established in...

Treatment of Latent TB Infection

Treatment of latent TB infection, formerly termed TB preventive therapy, has two principal benefits an individual health benefit through prevention of TB and an important benefit to the community wherein decreased transmission and new M. tuberculosis infections will lead to an eventual lowering of case rates in the entire population. Interest in the use of isoniazid to prevent TB disease in people with previous M. tuberculosis infection began in the late 1950s. In HIV-noninfected people, 6 to...

Yaws

Yaws is a disease of children (peak incidence at age 2 to 10 years) that is most common in warm, humid regions, including South and Central America, the Caribbean, equatorial Africa, and the equatorial islands of Southeast Asia.7,10,11 The prevalence and incidence of yaws declined markedly during the yaws eradication campaigns of the 1950s, but in recent years the disease has again become more common. The infection is spread mainly by direct exposure to infectious lesions containing treponemes,...

Overview And Terminology Measures of Disease Frequency

Prevalence is a measure of the total number of existing cases of a disease or condition in a specific population at a particular time. Prevalence is usually expressed as a fraction or percentage of a population, but it can also be given as the number of cases per 1000, 10,000, or 100,000 people. In contrast to prevalence, which enumerates all cases of a disease, incidence is a measure of the number of new cases of disease occurring over a specified period. Incidence is, therefore, expressed as...

Interactions with Macrophages and Systemic Infection

Salmonellae are facultative intracellular pathogens, and available data from both animal models of infection and humans with enteric fever suggest that bacterial replication within macrophages is essential for production of systemic disease. The role of intracellular bacterial replication in human gastroenteritis due to nontyphoidal serotypes is less clear, but it is likely that the ability of salmonellae to resist killing by macrophages contributes to the cases of bacteremia and systemic...

Organisms

Rickettsiae are small (0.3 X 1.0 lm) obligately intracellular bacteria with a gram-negative cell wall that reside free in the cytosol of human endothelial cells and various cells of their arthropod hosts. The family Rickettsiaceae contains the genera Rickettsia and Orientia. The genus Rickettsia is divided into the typhus and spotted fever groups on the basis of antigenic differences in the immunodominant lipopolysaccharides (LPS) the presence of outer membrane protein A (OmpA) in SFG...

Antigen and Nucleic Acid Probes

In recent years, other nonculture diagnostic methods have been evaluated and widely used, including DFA, EIA, and DNA probe methods. There are a number of DFA kits commercially available. Although they differ primarily in their specificity and in their ease of laboratory use, the general principle is the same. A cytologic smear is fixed (at which stage it can be stored), stained with a fluorescein-conjugated monoclonal antibody, and examined by ultraviolet microscopy. Elementary bodies are...

Innate Immunity Physical Barriers

The primary physical barrier to infection, the integument, is affected by a wide variety of nutrient deficiencies. Skin lesions are one of the cardinal signs of kwashiorkor. Protein energy malnutrition or even more milder forms of nutritional depletion can be correlated with decreased gastrointestinal mucosal integrity as measured by the lactulose mannitol ratio.125 Also, vitamin A deficiency has been found to have a similar effect on gut integrity by the same test.126 Striking histological...

Vaccines

The capacity to elicit protective immunity against infectious agents was first achieved 200 years ago with the utilization of vaccinia (cowpox) by Jenner to protect against smallpox. The word vaccination derives from this first success. Immunization was critical in eradicating smallpox from the world and underlies the approach to the global eradication of other infections, including poliomyelitis. With the vaccines currently recommended by the World Health Organization (WHO) Expanded Programme...

Economic Costs and Adherence to HIV Therapy

As HIV treatment programs in resource-poor settings undergo expansion, advocates and pundits alike agree that medication adherence is paramount to the success of these initiatives. But early data have already shown that adherence is significantly reduced in programs in which patients are forced to pay even nominal fees for their medications. Of 137 Ugandan patients being treated with antiretro virals (ARVs), nearly 33 had dropped out of therapy within 38 weeks many of them evidenced...

Communications

A final component of surveillance is the ability to rapidly and reliably exchange information on disease incidence and distribution, preferably in real time. Disease intelligence relies on formal and informal networks for dissemination and sharing of timely, accurate information on occurrences and outbreaks of infectious diseases and diffusion of prevention recommendations. One of the key lessons that emerged from the 2003 global SARS epidemic was the importance of networks of laboratory...

Isolation

The method of choice for recovery of C. trachomatis is by cell culture using McCoy, HeLa-229, BHK-21, or L-929 cells. A necessary step in cell cultivation of C. trachomatis strains other than LGV is centrifugation of the inoculum onto the cells. In addition, the cells are treated to enhance infection Gordon and colleagues, who developed the modern cell culture technique, used irradiation of McCoy cells.31 Cycloheximide has been substituted for irradiation, and cycloheximide-treated McCoy cells...

Agent Neorickettsia Sennetsu

Originally recognized as an illness mimicking infectious mononucleosis in Japan, N. sennetsu infections have subsequently been documented in Malaysia and might occur unrecognized in other areas of Asia where raw or undercooked fish are eaten.148,149 Recent investigations have identified complex cycles of bacterial infection of trematodes, the cercariae of which may infect snails and aquatic insects.150 These are in turn ingested by a variety of animals, including fish, mammals, and birds, that...

B

Walled-off fibrocaseous lesions in the lung and other organs seeded during the initial bacillemia. These foci may break down years to decades later in the presence of waning immunity to produce active local or disseminated disease. The lungs are the most common site of reactivation TB. Chronic cough productive of purulent sputum of greater than 2 or 3 weeks' duration, night sweats, weight loss, and anorexia are the most frequent complaints. From 40 to 60 of patients are afebrile at...

Immunoprophylaxis

Shortly after the recognition of sulfonamide-resistant meningococci, and the obvious implications for prevention of secondary cases through chemoprophylaxis, efforts to develop immunogenic vaccines against the major meningo-coccal serogroups intensified.132 While immunity is variable following vaccination, no current commercially available meningococcal polysaccharide vaccine is immunogenic in children under 24 months of age and therefore chemopro-phylaxis is a primary strategy in day-care...

Antibiotics

The objectives of antibiotic treatment are to reduce the pool of chlamydial infection in the community and the severity of active trachoma, and thus of the risk of blindness, in individual cases. Sulfonamides, tetracyclines, erythromycin, other macrolides and azalides, and rifampin are effective against trachoma. Most control programs utilized topical tetracycline ointment from the 1950s to the mid-1990s. Antibiotic treatment in endemic communities (active trachoma in more than 20 of children)...

Antimicrobial Therapy

Appropriate antibiotics significantly decrease the duration of diarrhea, the total diarrheal stool volume, and the duration of excretion of V cholerae, and therefore serve as an important adjunct to rehydration therapy. Except for East Africa and a few other areas where tetracycline-resistant vibrios are endemic, tetracycline remains the drug of choice for all ages. The recommended pediatric dosage is 50 mg kg day in four divided doses for 3 to 5 days, whereas the regimen for teenagers and...

Epidemiology And Transmission

H. pylori infects more than 70 of persons in most developing countries and about 30 of persons in developed countries. In societies that have recently emerged to affluence (such as Japan), H. pylori is still quite common and infects most persons over the age of 40 years. H. pylori is acquired in childhood, probably by the fecal-oral route. The bacterium has been isolated from the feces of children in The Gambia18 and polymerase chain reaction (PCR) techniques have demonstrated the genome of the...

Chemoprophylaxis

In endemic areas or epidemic areas where secondary transmission within households is shown to be a frequent event, a short (3-day) course of tetracycline (or another cited antibiotic) administered to household contacts can diminish transmission within households.81 However, such use of antibiotics must be strictly controlled because indiscriminate use in the community can rapidly lead to antibiotic resistance. This was the situation in Guayaquil, Ecuador, in 1991 following the introduction of...

Replication

Recent evidence suggests that both NiV and HeV bind to the same glycoprotein receptor by a mechanism that is independent of sialic acid mediation.32 Cleavage of HeV and NiV fusion protein precursor F0 into disulfide-linked F1 and F2 subunits is a prerequisite for infectivity and is achieved by mechanisms unlike those of other paramyxoviruses.33,34 Recent minigenome-based studies indicate that the sequence elements that control NiV and HeV replication reside in the noncoding genomic and...

Hymenoptera

A significant percentage of the world's population is at risk of life-threatening anaphylactic reactions to Hymenoptera stings. In the United States, for example, somewhere between 0.5 and 5.0 of the population is severely allergic to these venoms.58 The three superfamilies of major medical importance in this order are the Apoidea (honeybees and bumblebees), the Vespoidea (wasps, yellow jackets, and hornets), and the Formicoidea (ants). Hymenoptera venoms are complex mixtures of biogenic amines...

Human Immunodeficiency Virus

There is variability in the natural history of HIV infection. Three categories of infected people have attracted attention those who progress rapidly, long-term nonprogressers (LTNP), Table 6-6 Examples of Non-MHC and Class III MHC Genes with Allele-Specific Associations with Malaria Table 6-6 Examples of Non-MHC and Class III MHC Genes with Allele-Specific Associations with Malaria