
Full text loading...
Category: Clinical Microbiology
Ebook: Choose a downloadable PDF or ePub file. Chapter is a downloadable PDF file. File must be downloaded within 48 hours of purchase
Emerging Infections 3 is the third of an annual series of books based on ICAAC Symposia on Emerging Infections. It provides a complete and updated discussion of new and emerging infectious diseases, covering both basic science and clinical topics. The editors are in the forefront of the scientific and clinical communities dealing with emerging pathogens. This book and the series will be valuable to a wide range of people working in microbiology, infectious diseases, epidemiology, public health, and clinical medicine.
This book is no longer available in print.
Electronic book, 260 pages, illustrations, index.
Hepatitis E virus (HEV) is the most recently characterized of five viruses known to produce the majority of cases of hepatitis worldwide. Limited studies suggest that a substantial proportion of cases of acute viral hepatitis in Asia, the Indian subcontinent, and Africa is due to HEV infection. At the time of the epidemic, virus-specific diagnostic tests were not available and the disease was thought to be due to a variant of HAV that overwhelmed host immunity. Subsequent testing of stored specimens demonstrated that these patients did not have acute HAV or acute HBV infection. This newly identified disease was called enterically transmitted non-A, non-B hepatitis and suggested the presence of at least one other hepatitis virus. Prior to production of HEV antigens by recombinant DNA technology, anti-HEV was detected by immune electron microscopy with stool-derived virus or by blocking fluorescent microscopy with antigen from the liver of infected macaques. Subsequently, recombinant expressed proteins and synthetic peptides, primarily from open reading frame (ORF) 2, have been used to develop immunoblotting assays and enzyme immunoassays for the detection of anti-HEV activity. Amplification of RNA by reverse transcription-PCR (RT-PCR) has been used to detect HEV RNA in the stools of experimentally infected animals, as well as in humans with hepatitis E. Early studies indicated that active immunization with recombinant ORF2 proteins provided some protection from infection in the cynomolgus macaque model.
Rickettsioses present some of the oldest recognized infectious diseases. Ricketts proved that the wood tick Dermacentor andersoni, was involved in the transmission of the Rocky Mountain spotted fever (RMSF). In 1910, the first cases of Mediterranean spotted fever (MSF) were reported in Tunis, Tunisia. The role of Rhipicephalus sanguineus was established in 1930. Prior to 1984, only eight rickettsioses were recognized, and in the subsequent 13 years, seven new rickettsial diseases were described. The advent of novel diagnostic tools has dramatically improved the efficiency of diagnosis of rickettsioses and the recognition of new rickettsial species. Cell culture is the most widely used system for primary isolation. The oriental rat flea, Xenopsylla cheopis, is the main flea vector of flea-borne bacterial diseases, including rickettsioses. These fleas are associated with Old World commensal rats, and consequently, the disease associated with these fleas is prevalent in harbors and large cities, The cat flea, Ctenocephalides felis, is the vector for cat-scratch disease and cat-flea typhus. Eleven new rickettsioses have been described since 1974. An entirely new clinical entity, such as the one caused by R. slovaca, which results in disease without the typical rash associated with other spotted fevers was described. The future of such new diseases is unpredictable because rickettsioses have not been systematically studied in such cases. This is an area for future research.
Decades after the early industrial era, nontyphoidal salmonella emerged as a common cause of illness. Much of this increase is accounted for by two serotypes, Salmonella Enteritidis and Salmonella Typhimurium, which now account for nearly half of all cases of salmonellosis in the United States and for 82% of all cases of salmoneIlosis in a recent global survey. Mice may play an important role in the barnyard ecosystem, serving as the intermediate host that can pass Salmonella Enteritidis from one chicken flock to the next group of chicks entering the henhouse. Within Salmonella Enteritidis, phage typing defines a handful of dominant subtypes, each of which tends to be remarkably homogeneous. One interesting line of evidence comes from examination of strains that vary in their ability to colonize the ovary of an intact hen after oral feeding. Salmonella Typhimurium has been among the most common of serotypes everywhere ever since serotyping began. The genetic structure of the resistance genes of OTl 04 is beginning to be mapped. All five genes are chromosomally located. The clinical features of DTI 04 infections are similar to those of nontyphoid salmonellosis in general. Prevention of Salmonella Enteritidis and DT104 infections in humans depends on interruption of their flow from farm reservoirs to human foods. The public health challenge by both pathogens described in this chapter illustrates the intimate connection between the microbial ecology of food animals and the health of the consuming public.
The aquaculture industry, which is increasingly being developed, has not yet been recognized to result in significant human disease. Aquaculture in North America involves diverse farming systems in diverse areas. The criticisms concern contamination of the environment by aquaculture systems through unwanted obstructions to coastal navigation, unsightly cages or pens, aquaculture effluents such as excess food and chemotherapeutics, and the use of nonnative species or native species that are either domesticated or genetically different from wild stocks. The level of contamination of aquaculture products with pathogenic bacteria depends on the environment and the bacteriological quality of the water where the fish are cultured. It should be noted that nonindigenous bacteria of fecal origin could be introduced into aquaculture ponds via contamination by birds and wild animals associated with farm waters. Streptococcus iniae has also been reported to be the causative agent of ongoing infection and excess mortality of tilapia in Texas aquaculture farms. Overcrowding in farms and during transport may have contributed to the increasing importance of streptococcal infections in fish. Finally, although S. iniae commonly colonized the surfaces of tilapia and other species of fish, isolates are genetically diverse. Although S. iniae is capable of causing invasive disease in humans, serious disease appears to be rare, and if people take the proper precautionary measures when handling whole, uncooked fish, infections caused by S. iniae can be prevented.
The impact of louse-borne, or epidemic, typhus, which is caused by Rickettsia prowazekii, on populations is of historical significance but has passed from current concern. Whenever large numbers of people were crowded together under less than sanitary conditions, typhus appeared. Louse-borne typhus remains endemic in the mountainous regions of the Americas, the Himalayas, Afghanistan, and Africa. The disease is maintained in an endemic cycle of transmission that remains barely detectable. Occasionally, conditions that favor epidemic transmission occur. Epidemic typhus spreads into populations at higher elevations, where colder conditions prevailed and infestations with lice were prevalent. Epidemic typhus is characterized clinically by sudden onset, sustained high fever of about 2 weeks duration, a maculopapular rash, and altered mental state. There is effective antimicrobial therapy for the typhus fevers. The response to tetracyclines or chloramphenicol is rapid and efficacious. Most patients become afebrile within 48 h of treatment, and single-dose doxycycline therapy is effective in epidemic situations. Strategies for control of epidemics of louse-borne typhus in refugee camps must include two elements of intervention: (i) antimicrobial treatment of patients with suspected cases and (ii) delousing of the entire population at risk. Long-term louse control or eradication depends on correction of the complex environmental, economic, cultural, educational, and political factors that contribute to louse infestations.
Microsporidia have risen from obscure and anecdotal causes of keratitis and systemic disease in humans to become one of the most medically significant groups of emerging infectious agents. This chapter focuses on what is known regarding the epidemiology of human microsporidiosis and what we may be poised to better understand in the very near future. Topics covered include prevalence and geographic distribution, case demographics and populations at risk, and potential modes of transmission. The most common clinical presentation of Encephalitozoon intestinalis infection, similar to that of Encephalitozoon bieneusi infection, is severe chronic diarrhea, which often progresses to malabsorption and wasting syndrome. Surveys for antibodies to microsporidia in human sera have focused exclusively on human exposure to Encephalitozoon species. Although most recognized cases of human microsporidiosis are associated with some form of immunosuppression, reports describing microsporidial infections in HIV-negative, immunocompetent patients are also increasing. Microsporidia have been isolated from ditch water in a mosquito larval habitat in Florida. The only two factors which were associated with microsporidian infection were swimming in a pool and male homosexuality. One of the most exciting observations in the prevention of microsporidiosis in persons with AIDS has been the role of highly active antiretroviral therapy (HAART) in raising CD4 lymphocyte counts and heightening immunity. A high standard of personal hygiene seems mandatory for patients infected with microsporidia. Cohabitating sexual partners of infected patients should be offered screening for microsporidiosis regardless of their HIV status.
During the past decade, there has been an increase in numbers of new cases, spread of the disease into new regions, and even appearance of new clinical syndromes. This resurgence of leishmaniasis reflects the remarkable adaptability of the Leishmania parasite to changing conditions, such as those resulting from economic development, human modification of the environment, and population movements. In visceral leishmaniasis, or kala-azar, there is infection of reticuloendothelial cells throughout the body and particularly in the liver, spleen, bone marrow, and lymphoid tissue. In cutaneous leishmaniasis, parasite replication is confined primarily to the skin. Treatment is required for persons with clinically apparent visceral leishmaniasis, mucocutaneous leishmaniasis, and cases of cutaneous leishmaniasis in which spontaneous healing is slow, lesions involve the face, or infection is due to species that can cause mucocutaneous leishmaniasis or diffuse cutaneous leishmaniasis. The gold standard treatment is pentavalent antimony given intravenously or intramuscularly at a dose of 20 mg/kg/day for a minimum of 20 days. Visceral leishmaniasis in HIV-infected persons is associated with higher levels of parasitemia than is seen in non-HIV-infected persons, and sand flies readily acquire parasites from coinfected persons. Measures to control the spread of visceral leishmaniasis in Teresina have focused on identifying and killing infected dogs, and application of insecticide in the neighborhoods surrounding new cases of frank kala-azar. High among the priorities for research on leishmaniasis is the development of new methods for predicting the occurrence of outbreaks and establishment of new foci of transmission.
In the United States it is important to keep in mind that imported cases among tourists returning from countries where acute Chagas' disease is endemic have not been reported and that autochthonous Trypanosoma cruzi infections are extremely rare. Even though T. cruzi-infected triatomine insects are present in many parts of the western and southern United States, only four autochthonous cases of acute Chagas' disease have been reported. Importantly, none of the imported cases occurred in tourists returning to the United States, but two such instances have been reported in Europe. Although the number of imported and autochthonous cases of acute Chagas’ disease that go unrecognized may be several times the number described, the fact is that acute T. cruzi infection is rare in the United States, and there is no reason to expect that this situation will change. The courses of acute Chagas’ disease in the transfusion recipients were particularly severe because of immunosuppressive treatments that they were receiving, and no doubt this contributed to the specific diagnosis. Finally, an antifungal agent, bis-triazole (00807), was recently reported to cure acute T. cruzi infections in mice, but it is still in the early stages of development. Management of the occasional severely ill patient with chagasic meningoencephalitis or myocarditis is for the most part supportive. Cardiac transplantation is an option for patients with end-stage chagasic heart disease.
Presumptive exposure to toxins produced by Pfiesteria piscicida, a small dinoflagellate found in mid-Atlantic estuarine waters, emerged as the cause of a novel human health syndrome of impaired cognition associated with skin rash, headache, gastrointestinal symptoms, and respiratory complaints following fish-kill events in Maryland's Chesapeake Bay in 1997. Dinoflagellates meet their nutritional needs either by photosynthesis (autotrophy), phagocytosis of food sources (heterotrophy), or combinations of these strategies (mixotrophy). Blooms of populations of these and other organisms that affect environmental quality and, at times, human health are often considered collectively under the general topic of harmful algal bloom (HAB). Toxin production by marine and estuarine dinoflagellates is responsible for four human health syndromes. Many fish collected during Pfiesteria-related fish-kill events display aberrant swimming behavior and have diffuse epithelial injury, with hemorrhage and necrosis. No consistent or unexpected abnormalities were found on physical examination. As outlined in this chapter, much remains to be learned about the organism, its presumed toxins, the environmental conditions which promote toxin expression, and the mechanisms by which these toxins might cause disease in humans. At the same time, there is an increasing convergence of data which support the idea of a link between exposure to toxins produced by this and related dinoflagellates and the occurrence of illness in humans.
In 1997, a huge outbreak of foot-and-mouth disease (FMD) emerged in Taiwan. Although the source of the outbreak was never confirmed, there were strong suspicions that it resulted from illegal importation of infected animals. All of these large-scale outbreaks of diseases emergent in countries that have been free of them usually result in massive depopulation of herds or flocks. This depopulation in and of itself can have significant impacts on humans. First, for each food-producing animal that is killed, there is considerable resource wastage; that is, all of the materials required to grow the animal are never recovered in the form of consumable protein. Second, there can be major environmental problems associated with the disposal of carcasses. In general, the animals and animal products that cross borders are subject to stringent regulatory controls related to those diseases with which the scientific agricultural community is already familiar. In animals there are numerous examples of alterations in ecology that have resulted in new diseases. As animals are moved around and grouped in new ways, as their environments are modified, and as technological advances to increase production are promoted, there is tremendous potential for endogenous flora to wedge into new gaps. Husbandry changes, the correlate of which in human medicine would be lifestyle changes, are responsible for a number of emerging diseases in animals. There are a variety of emerging diseases of animals, and they are caused by many of the same factors that are at play in human diseases.
Xenotransplantation refers to the therapeutic use of living animal tissue in humans. Xenotransplantation has the potential to infect human recipients with agents that are not endemic in human populations, thereby introducing new infections to the human community (xenogeneic infections). The Public health service (PHS) draft guideline on infectious disease issues in Xenotransplantation emphasizes the importance of including experts in human and veterinary infectious diseases and microbiology on the xenotransplantation team. In addition to emphasizing the importance of screening and surveillance, the PHS draft guideline on infectious disease issues in Xenotransplantation recommends that archives of biologic specimens obtained from the xenograft source animals and human recipients both before and at intervals following the xenotransplantation be maintained. The absence of recognized disease attributable to foamy virus in infected animals of any species, including the small numbers of SFV-infected humans studied to date, combined with the absence of identified secondary transmission among humans, have led some experts to argue that foamy virus infections of humans are benign end-point infections of no significance to human health. Efforts to address issues in xenotransplantation have accomplished much in a short time. Major research questions have been framed, an infrastructure for public policy has been outlined, and tools that enable the science necessary to define whether endogenous retroviruses pose a risk to human xenograft recipients have been developed and deployed.
Due to increased awareness of infectious diseases, there has been renewed interest and revitalization in infectious disease pathology. Recent experience at the Centers for Disease Control and Prevention (CDC) and other institutions has shown that use of a combination of traditional morphology with immunologic and molecular pathology techniques is an extremely useful approach for the confirmation of diagnoses for patients with otherwise unexplained illnesses. Visualization of microbial antigens or nucleic acids in the context of pathology allows the pathologist to assess the clinical significance of serologic test results or microbial isolation. By comparison, the use of molecular pathology techniques offers several distinct advantages over traditional microbiologic methods, including speed, sensitivity, reduced risk of exposure of laboratory personnel to the agent, and tissue localization of pathogens. Epidemiologic, clinical, and histopathologic findings enable CDC pathologists to use the most appropriate initial immunologic and molecular pathology tests. The chapter highlights some of the contributions of CDC pathologists in addressing some of the challenges posed by new, emerging, and reemerging infectious diseases. Historically, pathologists and the discipline of pathology have played pivotal roles in the discovery and characterization of the rickettsioses and, more recently, the ehrlichioses. Disease recognition by infectious disease pathologists can play a key role in the study of emerging infectious diseases. The chapter provides several examples of the frontline role of pathology in guiding the early phases of epidemiologic investigations of infectious diseases.
This chapter describes the use of medical examiner or coroner (ME/C) data for public health surveillance, provides an overview of surveillance for fatal infectious conditions, and describes ongoing efforts aimed at identifying the most complete and accurate methods for incorporating ME/C-based autopsy data into state-based and national surveillance systems. In contrast to retrospective surveillance methods, the Centers for Disease Control and Prevention (CDC) in 1994 began active surveillance for infectious disease with the establishment of the Emerging Infections Program (EIP) at four sites in the United States. Sections in the chapter discuss issues related to the incorporation of ME/Cs into the overall surveillance for infectious diseases, including those from bioterrorist attacks, and describe the potential advantages and limitations of this data source. In New Mexico, approximately 25% of autopsied natural deaths are infectious disease related. Because some of these deaths are caused by emerging infections, it is likely that ME/Cs could play an important role in surveillance for these conditions nationally. In recognition of this fact, CDC’s 1994 emerging infections plan identifies medical examiners as an important sentinel surveillance network. Any system that is implemented to conduct surveillance for acts of bioterrorism should involve medicolegal death investigators for several reasons. First, medical examiners and coroners may see cases of fatal unattended infections from acts of bioterrorism that other physicians, hospitals, or emergency rooms have not seen. Directing autopsy pathologists to search for emerging infections is not without some element of danger.
The recognition of and response to actual terrorist use of an infectious agent are complicated. In contrast to chemical agents or explosive devices, whose destructive impacts are immediately recognizable, covert delivery of biological agents in the absence of notification of intent would cause disease only after an incubation period during which exposed persons could be widely dispersed. Immunohistochemical staining of autopsy tissues confirmed the existence of a previously unrecognized hantavirus approximately 1 month after the initial recognition of cases of the syndrome, but several months elapsed before the virus was finally isolated in cell culture. This experience highlights the critical importance of highly trained field and laboratory personnel, appropriate biocontainment facilities, and the laboratory reagents and sophisticated molecular techniques, all of which must be available for the detection of candidate agents that terrorists might use. The potential for bioterrorism emphasizes the urgency of strengthening the public health capacity to detect and respond to emerging infectious diseases, particularly the need to forge and strengthen partnerships between the public health and emergency response sectors. Centers for Disease Control and Prevention (CDC) maintains expertise in the detection of virtually all infectious agents pathogenic for humans and is able to use modem molecular techniques, traditional procedures for organism cultivation. Whether epidemics are the result of terrorism or natural factors, CDC and the public health community remain at the forefront of the global epidemic response.
Full text loading...