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Volume 3, Number 3—September 1997

Volume 3, Number 3—September 1997   PDF Version [PDF - 14.55 MB - 154 pages]

Perspective

  • Recombination in HIV: An Important Viral Evolutionary Strategy PDF Version [PDF - 38 KB - 7 pages]
    D. S. Burke
        View Abstract

    Human immunodeficiency virus (HIV) is a diploid virus: each virion carries two complete RNA genomic strands. Homologous recombination can occur when a cell is coinfected with two different but related strains. Naturally occurring recombinant HIV strains have been found in infected patients in regions of the world where multiple genotypic variants cocirculate. One recombinant HIV strain has spread rapidly to millions of persons in Southeast Asia. Recombination is a mechanism whereby high level and multidrug-resistant strains may be generated in individual treated patients. Recombination also poses theoretical problems for the development of a safe HIV vaccine. Certain features of HIV replication, such as syncytium formation and transactivation, may be best understood as components of a sexual reproductive cycle. Recombination may be an important HIV evolutionary strategy.

  • Host Genes and HIV: The Role of the Chemokine Receptor Gene CCR5 and Its Allele (∆32 CCR5) PDF Version [PDF - 394 KB - 12 pages]
    J. M. McNicholl et al.
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    Since the late 1970s, 8.4 million people worldwide, including 1.7 million children, have died of AIDS, and an estimated 22 million people are infected with human immunodeficiency virus (HIV) (1). During 1995 and 1996, major clinical and laboratory discoveries regarding HIV pathogenesis provided new hope for the prevention and treatment of HIV infection. One major discovery was that members of the chemokine receptor family serve as cofactors for HIV entry into cells. We describe the role of allelic polymorphism in the gene coding for the CCR5 chemokine receptor with regard to susceptibility to and disease course of HIV infection. We also examine the effect of this discovery on medical and public health practices.

  • Resistance, Remission, and Qualitative Differences in HIV Chemotherapy PDF Version [PDF - 224 KB - 11 pages]
    D. E. Kirschner and G. Webb
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    To understand the role of qualitative differences in multidrug chemotherapy for human immunodeficiency virus (HIV) infection in virus remission and drug resistance, we designed a mathematical system that models HIV multidrug chemotherapy including uninfected CD4+ T cells, infected CD4+ T cells, and virus populations. The model, which includes the latent and progressive stages of the disease and introduces chemotherapy, is a system of differential equations describing the interaction of two distinct classes of HIV (drug-sensitive [wild type] and drug-resistant [mutant]) with lymphocytes in the peripheral blood; the external lymphoid system contributes to the viral load. The simulations indicate that to preclude resistance, antiviral drugs must be strong enough and act fast enough to drive the viral population below a threshold level. The threshold depends upon the capacity of the virus to mutate to strains resistant to the drugs. Above the threshold, mutant strains rapidly replace wild-type strains. Below the threshold, resistant strains do not become established, and remission occurs. An important distinction between resistance and remission is the reduction of viral production in the external lymphoid system. Also the virus population rapidly rebounds when treatment is stopped even after extended periods of remission.

  • Emerging Foodborne Diseases PDF Version [PDF - 108 KB - 9 pages]
    S. Altekruse et al.
        View Abstract

    The epidemiology of foodborne diseases is rapidly changing. Recently described pathogens, such as Escherichia coli O157:H7 and the epidemic strain of Salmonella serotype Typhimurium Definitive Type 104 (which is resistant to at least five antimicrobial drugs), have become important public health problems. Well-recognized pathogens, such as Salmonella serotype Enteritidis, have increased in prevalence or become associated with new vehicles. Emergence in foodborne diseases is driven by the same forces as emergence in other infectious diseases: changes in demographic characteristics, human behavior, industry, and technology; the shift toward a global economy; microbial adaptation; and the breakdown in the public health infrastructure. Addressing emerging foodborne diseases will require more sensitive and rapid surveillance, enhanced methods of laboratory identification and subtyping, and effective prevention and control.

  • DDT, Global Strategies, and a Malaria Control Crisis in South America PDF Version [PDF - 160 KB - 8 pages]
    D. R. Roberts et al.
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    Malaria is reemerging in endemic-disease countries of South America. We examined the rate of real growth in annual parasite indexes (API) by adjusting APIs for all years to the annual blood examination rate of 1965 for each country. The standardized APIs calculated for Brazil, Peru, Guyana, and for 18 other malaria-endemic countries of the Americas presented a consistent pattern of low rates up through the late 1970s, followed by geometric growth in malaria incidence in subsequent years. True growth in malaria incidence corresponds temporally with changes in global strategies for malaria control. Underlying the concordance of these events is a causal link between decreased spraying of homes with DDT and increased malaria; two regression models defining this link showed statistically significant negative relationships between APIs and house-spray rates. Separate analyses of data from 1993 to 1995 showed that countries that have recently discontinued their spray programs are reporting large increases in malaria incidence. Ecuador, which has increased use of DDT since 1993, is the only country reporting a large reduction (61%) in malaria rates since 1993. DDT use for malaria control and application of the Global Malaria Control Strategy to the Americas should be subjects of urgent national and international debate. We discuss the recent actions to ban DDT, the health costs of such a ban, perspectives on DDT use in agriculture versus malaria control, and costs versus benefits of DDT and alternative insecticides.

  • Emerging and Reemerging Helminthiases and the Public Health of China PDF Version [PDF - 157 KB - 8 pages]
    P. J. Hotez et al.
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    Despite great strides in their control throughout the People's Republic of China, helminth infections remain an important public health problem. The Institute of Parasitic Diseases of the Chinese Academy of Preventive Medicine, under the guidance of the Chinese Ministry of Health, completed a nationwide survey of more than 1 million people that showed the high prevalence and intensity of intestinal nematode infections; prevalence can sometimes exceed 50% in the Yangtze River valley provinces. Schistosoma japonicum is also a major cause of illness in this region. Attempts to control Chinese helminthic diseases with conventional anthelminthic drugs have been partially thwarted by high posttreatment rates of reinfection. Recently, several new human trematode pathogens have been identified. Novel approaches to chemoprophylaxis and vaccination may alleviate the public health problem caused by Chinese helminths. However, recombinant helminth vaccine development will depend on first cataloguing the extensive genetic diversity of Chinese helminths and candidate vaccine antigens. Evidence from biogeography, genetics, and systematics suggests that the genetic diversification of Chinese helminths and their vectors is an ongoing evolutionary process that began 12 million years ago near the convergence of major Asian river systems. Construction of the Three Gorges Super Dam on the Yangtze River may promote the emergence and reemergence of new helminths and their snail vectors.

Synopses

  • Vancomycin-Resistant Enterococci Outside the Health-Care Setting: Prevalence, Sources, and Public Health Implications PDF Version [PDF - 57 KB - 7 pages]
    L. C. McDonald et al.
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    Although nosocomial acquisition and subsequent colonization of vancomycin-resistant enterococci (VRE), an emerging international threat to public health, has been emphasized in the United States, colonization among nonhospitalized persons has been infrequently documented. In contrast, in Europe, colonization appears to occur frequently in persons outside the health-care setting. An important factor associated with VRE in the community in Europe has been avoparcin, a glycopeptide antimicrobial drug used for years in many European nations at subtherapeutic doses as a growth promoter in food-producing animals. In Europe, evidence suggests that foodborne VRE may cause human colonization. Although avoparcin has never been approved for use in the United States, undetected community VRE transmission may be occurring at low levels. Further studies of community transmission of VRE in the United States are urgently needed. If transmission with VRE from unrecognized community sources can be identified and controlled, increased incidence of colonization and infection among hospitalized patients may be prevented.

  • Flea-borne Rickettsioses: Ecologic Considerations PDF Version [PDF - 434 KB - 9 pages]
    A. F. Azad et al.
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    Ecologic and economic factors, as well as changes in human behavior, have resulted in the emergence of new and the reemergence of existing but forgotten infectious diseases during the past 20 years. Flea-borne disease organisms, e.g., (Yersinia pestis, Rickettsia typhi, R. felis, and Bartonella henselae) are widely distributed throughout the world in endemic-disease foci, where components of the enzootic cycle are present. However, flea-borne diseases could reemerge in epidemic form because of changes in vector-host ecology due to environmental and human behavior modification. The changing ecology of murine typhus in southern California and Texas over the past 30 years is a good example of urban and suburban expansion affecting infectious disease outbreaks. In these areas, the classic rat-flea-rat cycle of R. typhi has been replaced by a peridomestic animal cycle involving, e.g., free-ranging cats, dogs, and opossums and their fleas. In addition to the vector-host components of the murine typhus cycle, we have uncovered a second typhuslike rickettsia, R. felis. This agent was identified from the blood of a hospitalized febrile patient and from opossums and their fleas. We reviewed the ecology of R. typhi and R. felis and present recent data relevant to the vector biology, immunology, and molecular characterization and phylogeny of flea-borne rickettsioses.

  • Aedes albopictus in the United States: Ten-Year Presence and Public Health Implications PDF Version [PDF - 330 KB - 6 pages]
    C. G. Moore and C. J. Mitchell
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    Since its discovery in Houston, Texas, in 1987, the Asian "tiger mosquito" Aedes albopictus has spread to 678 counties in 25 states. This species, which readily colonizes container habitats in the peridomestic environment, was probably introduced into the continental United States in shipments of scrap tires from northern Asia. The early pattern of dispersal followed the interstate highway system, which suggests further dispersal by human activities. The Public Health Service Act of 1988 requires shipments of used tires from countries with Ae. albopictus to be treated to prevent further importations. Given the extensive spread of the mosquito in the United States, it is questionable whether such a requirement is still justified. Ae. albopictus, a major biting pest throughout much of its range, is a competent laboratory vector of at least 22 arboviruses, including many viruses of public health importance. Cache Valley and eastern equine encephalomyelitis viruses are the only human pathogens isolated from U.S. populations of Ae. albopictus. There is no evidence that this mosquito is the vector of human disease in the United States.

  • Using a Mathematical Model to Evaluate the Efficacy of TB Control Measures PDF Version [PDF - 339 KB - 8 pages]
    L. Gammaitoni and M. C. Nucci
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    We evaluated the efficacy of recommended tuberculosis (TB) infection control measures by using a deterministic mathematical model for airborne contagion. We examined the percentage of purified protein derivative conversions under various exposure conditions, environmental control strategies, and respiratory protective devices. We conclude that environmental control cannot eliminate the risk for TB transmission during high-risk procedures; respiratory protective devices, and particularly high-efficiency particulate air masks, may provide nearly complete protection if used with air filtration or ultraviolet irradiation. Nevertheless, the efficiency of these control measures decreases as the infectivity of the source case increases. Therefore, administrative control measures (e.g., indentifying and isolating patients with infectious TB) are the most effective because they substantially reduce the rate of infection.

  • Borna Disease Virus Infection in Animals and Humans PDF Version [PDF - 196 KB - 10 pages]
    J. A. Richt et al.
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    The geographic distribution and host range of Borna disease (BD), a fatal neurologic disease of horses and sheep, are larger than previously thought. The etiologic agent, Borna disease virus (BDV), has been identified as an enveloped nonsegmented negative-strand RNA virus with unique properties of replication. Data indicate a high degree of genetic stability of BDV in its natural host, the horse. Studies in the Lewis rat have shown that BDV replication does not directly influence vital functions; rather, the disease is caused by a virus-induced T-cell--mediated immune reaction. Because antibodies reactive with BDV have been found in the sera of patients with neuropsychiatric disorders, this review examines the possible link between BDV and such disorders. Seroepidemiologic and cerebrospinal fluid investigations of psychiatric patients suggest a causal role of BDV infection in human psychiatric disorders. In diagnostically unselected psychiatric patients, the distribution of psychiatric disorders was found to be similar in BDV seropositive and seronegative patients. In addition, BDV-seropositive neurologic patients became ill with lymphocytic meningoencephalitis. In contrast to others, we found no evidence is reported for BDV RNA, BDV antigens, or infectious BDV in peripheral blood cells of psychiatric patients.

Dispatches

  • Deer Ticks (Ixodes scapularis) and the Agents of Lyme Disease and Human Granulocytic Ehrlichiosis in a New York City Park PDF Version [PDF - 26 KB - 3 pages]
    T. J. Daniels et al.
       
  • Jail Fever (Epidemic Typhus) Outbreak in Burundi PDF Version [PDF - 68 KB - 4 pages]
    D. Raoult et al.
        View Abstract

    We recently investigated a suspected outbreak of epidemic typhus in a jail in Burundi. We tested sera of nine patients by microimmunofluorescence for antibodies to Rickettsia prowazekii and Rickettsia typhi. We also amplified and sequenced from lice gene portions specific for two R. prowazekii proteins: the gene encoding for citrate synthase and the gene encoding for the rickettsial outer membrane protein. All patients exhibited antibodies specific for R. prowazekii. Specific gene sequences were amplified in two lice from one patient. The patients had typical clinical manifestations, and two died. Molecular techniques provided a convenient and reliable means of examining lice and confirming this outbreak. The jail-associated outbreak predates an extensive ongoing outbreak of louse-borne typhus in central eastern Africa after civil war and in refugee camps in Rwanda, Burundi (1), and Zaire.

  • Hantavirus Transmission in the United States PDF Version [PDF - 591 KB - 5 pages]
    R. M. Wells et al.
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    In 1996, investigation of a hantavirus pulmonary syndrome (HPS) outbreak in southern Argentina found evidence of person-to-person transmission of a hantavirus. The infection control ramifications of this finding led to this review of hantavirus epidemiology in the United States; the review suggests that Sin Nombre virus infection is rarely, if ever, transmitted from person to person and that existing guidelines for prevention of HPS remain appropriate for North America.

  • Population Dynamics of the Deer Mouse (Peromyscus maniculatus) and Sin Nombre Virus, California Channel Islands PDF Version [PDF - 120 KB - 4 pages]
    T. B. Graham and B. B. Chomel
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    Hantavirus pulmonary syndrome, first documented in 1993, is caused by Sin Nombre virus (SNV), which is carried by the Peromyscus species. In 1994, high SNV antibody prevalence was identified in deer mice from two California Channel Islands. We sampled two locations on three islands to estimate mouse population density and SNV prevalence. Population flux and SNV prevalence appear to vary independently.

  • Emerging Quinolone-Resistant Salmonella in the United States PDF Version [PDF - 20 KB - 2 pages]
    H. Herikstad et al.
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    We conducted a national survey of antimicrobial resistance in human clinical isolates of Salmonella between July 1, 1994, and June 30, 1995. Every tenth nontyphoidal Salmonella isolate received at state public health laboratories in the United States during this period was tested for resistance to 12 antimicrobial agents, including two quinolones, nalidixic acid, and ciprofloxacin. Emerging quinolone resistance was detected; of 4,008 isolates tested, 21 (0.5%) were resistant to nalidixic acid, and one (0.02%) was resistant to ciprofloxacin. Continued surveillance for quinolone-resistant Salmonella is necessary, particularly after the recent approval of a fluoroquinolone for use in animals intended for food in the United States.

  • Multidrug-Resistant Enteroaggregative Escherichia coli Associated with Persistent Diarrhea in Kenyan Children PDF Version [PDF - 21 KB - 2 pages]
    W. Sang et al.
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    To study the association of multidrug-resistant enteroaggregative Escherichia coli with persistent diarrhea in Kenyan children, stool specimens were obtained from 862 outpatients under 5 years of age from July 1991 to June 1993. E. coli O44 was identified as the sole bacterial pathogen in four patients experiencing at least 14 days of fever, vomiting, and diarrhea. Disk diffusion testing showed E. coli O44 resistance to tetracycline, ampicillin, erythromycin, trimethoprim-sulphamethoxazole, and amoxicillin/clavulanate and sensitivity to chloramphenicol, nalidixic acid, azithromycin, and cefuroxime. Further studies are needed to clarify the epidemiology, clinical spectrum, and pathogenesis of enteroaggregative E. coli infection.

  • Molecular Epidemiologic Investigations of Mycoplasma gallisepticum Conjunctivitis in Songbirds by Random Amplified Polymorphic DNA Analyses PDF Version [PDF - 119 KB - 6 pages]
    D. H. Ley et al.
        View Abstract

    An ongoing outbreak of conjunctivitis in free-ranging house finches (Carpodacus mexicanus) began in 1994 in the eastern United States. Bacterial organisms identified as Mycoplasma gallisepticum (MG) were isolated from lesions of infected birds. MG was also isolated from a blue jay (Cyanocitta cristata) that contracted conjunctivitis after being housed in a cage previously occupied by house finches with conjunctivitis, and from free-ranging American goldfinches (Carduelis tristis) in North Carolina in 1996. To investigate the molecular epidemiology of this outbreak, we produced DNA fingerprints of MG isolates by random amplification of polymorphic DNA (RAPD). We compared MG isolates from songbirds examined from 1994 through 1996 in 11 states, representing three host species, with vaccine and reference strains and with contemporary MG isolates from commercial poultry. All MG isolates from songbirds had RAPD banding patterns identical to each other but different from other strains and isolates tested. These results indicate that the outbreak of MG in songbirds is caused by the same strain, which suggests a single source; the outbreak is not caused by the vaccine or reference strains analyzed; and MG infection has not been shared between songbirds and commercial poultry.

  • Reevaluating the Molecular Taxonomy: Is Human-Associated Cyclospora a Mammalian Eimeria Species? PDF Version [PDF - 392 KB - 3 pages]
    N. J. Pieniazek and B. L. Herwaldt
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    Human-associated Cyclospora is a coccidian parasite that causes diarrheal disease. A reevaluation of the parasite's molecular taxonomy that takes into account newly published data for seven Eimeria species shows that Cyclospora belongs to the Eimeria clade (Eimeriidae family). The Cyclospora branch on the phylogenetic tree is between the branches of the eight avian and two mammalian Eimeria species that have been evaluated to date. Furthermore, preliminary results indicate that Cyclospora and Isospora belli, another coccidian parasite that causes diarrheal disease in humans, belong to different families. To improve our understanding of the taxonomy of human-associated Cyclospora, molecular evaluation of isolates of additional Cyclospora and Eimeria species is needed.

  • Rapid Increase in the Prevalence of Metronidazole-Resistant Helicobacter pylori in the Netherlands PDF Version [PDF - 38 KB - 5 pages]
    E. van der Wouden et al.
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    The prevalence of primary metronidazole resistance of Helicobacter pylori was studied in one Dutch hospital from 1993 to 1996 and in two additional Dutch hospitals in 1993 and 1996. All cultures of antral biopsy specimens yielding H. pylori in the study period were evaluated, except those from patients who had received anti-H. pylori treatment; 1,037 H. pylori strains, all from different patients were included. Metronidazole resistance was determined by disk diffusion in 1993 and by Epilipsometer-test in 1994 to 1996. Metronidazole resistance increased from 7% (18/245) in 1993 to 32% (161/509) in 1996. More patients with nonulcer dyspepsia and more non-Western European patients were seen in 1996 than in 1993, but age and sex differences were not observed. A comparable increase in metronidazole resistance was observed in both nonulcer dyspepsia patients and peptic ulcer patients, and the prevalence of metronidazole resistance in Western Europeans increased from 5% in 1993 to 28% in 1996.

  • An Increase in Hookworm Infection Temporally Associated With Ecologic Change PDF Version [PDF - 25 KB - 3 pages]
    B. Lilley et al.
        View Abstract

    This report describes a significant increase in the prevalence of hookworm infection in an area of Haiti where intestinal parasites are common, but hookworm has not been common. Changing environmental conditions, specifically deforestation and subsequent silting of a local river, have caused periodic flooding with deposition of a layer of sandy loam topsoil and increased soil moisture. We speculate that these conditions, conducive to transmission of the infection, have allowed hookworm to reemerge as an important human pathogen.

  • Using Laboratory-Based Surveillance Data for Prevention: An Algorithm for Detecting Salmonella Outbreaks PDF Version [PDF - 268 KB - 6 pages]
    L. C. Hutwagner et al.
        View Abstract

    By applying cumulative sums (CUSUM), a quality control method commonly used in manufacturing, we constructed a process for detecting unusual clusters among reported laboratory isolates of disease-causing organisms. We developed a computer algorithm based on minimal adjustments to the CUSUM method, which cumulates sums of the differences between frequencies of isolates and their expected means; we used the algorithm to identify outbreaks of Salmonella Enteritidis isolates reported in 1993. By comparing these detected outbreaks with known reported outbreaks, we estimated the sensitivity, specificity, and false-positive rate of the method. Sensitivity by state in which the outbreak was reported was 0% (0/1) to 100%. Specificity was 64% to 100%, and the false-positive rate was 0 to 1.

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