The contribution of genetic diversity to the spread of infectious diseases in livestock populations.
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This article uses stochastic simulations with a compartmental epidemic model to quantify the impact of genetic diversity within animal populations on the transmission of infectious disease. Genetic diversity is defined by the number of distinct genotypes in the population conferring resistance to microparasitic (e.g., viral or bacterial) infections. Scenarios include homogeneous populations and populations composed of few (finite-locus model) or many (infinitesimal model) genotypes. Genetic heterogeneity has no impact upon the expected value of the basic reproductive ratio (the primary description of the transmission of infection) but affects the variability of this parameter. Consequently, increasing genetic heterogeneity is associated with an increased probability of minor epidemics and decreased probabilities of both major (catastrophic) epidemics and no epidemics. Additionally, heterogeneity per se is associated with a breakdown in the expected relationship between the basic reproductive ratio and epidemic severity, which has been developed for homogeneous populations, with increasing heterogeneity generally resulting in fewer infected animals than expected. Furthermore, increased heterogeneity is associated with decreased disease-dependent mortality in major epidemics and a complex trend toward decreased duration of these epidemics. In summary, more heterogeneous populations are not expected to suffer fewer epidemics on average, but are less likely to suffer catastrophic epidemics. (+info)
Hepatic lesions in cetaceans stranded in the Canary Islands.
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This article describes the gross, histopathologic, and ultrastructural findings of the livers of cetaceans stranded on the coast of the Canary Islands between 1992 and 2000. A total of 135 cetaceans were included in the study, among which 25 were common dolphins (Delphinus delphis), 23 Atlantic spotted dolphins (Stenella frontalis), 19 striped dolphins (Stenella coeruleoalba), and 15 other species of dolphins and whales. The most common lesion observed in these animals was a nonspecific chronic reactive hepatitis (47/135), followed by hyaline intracytoplasmic inclusions in hepatocytes (33/135). Parasitic cholangitis was detected in 8/135 animals, whereas hepatic lipidosis was presented in 7/135 animals. The ultrastructure of hyaline hepatocytic cytoplasmic inclusions is described, and possible causes of these inclusions are discussed. (+info)
The elusive baseline of marine disease: are diseases in ocean ecosystems increasing?
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Disease outbreaks alter the structure and function of marine ecosystems, directly affecting vertebrates (mammals, turtles, fish), invertebrates (corals, crustaceans, echinoderms), and plants (seagrasses). Previous studies suggest a recent increase in marine disease. However, lack of baseline data in most communities prevents a direct test of this hypothesis. We developed a proxy to evaluate a prediction of the increasing disease hypothesis: the proportion of scientific publications reporting disease increased in recent decades. This represents, to our knowledge, the first quantitative use of normalized trends in the literature to investigate an ecological hypothesis. We searched a literature database for reports of parasites and disease (hereafter "disease") in nine marine taxonomic groups from 1970 to 2001. Reports, normalized for research effort, increased in turtles, corals, mammals, urchins, and molluscs. No significant trends were detected for seagrasses, decapods, or sharks/rays (though disease occurred in these groups). Counter to the prediction, disease reports decreased in fishes. Formulating effective resource management policy requires understanding the basis and timing of marine disease events. Why disease outbreaks increased in some groups but not in others should be a priority for future investigation. The increase in several groups lends urgency to understanding disease dynamics, particularly since few viable options currently exist to mitigate disease in the oceans. (+info)
Scabies: more than just an irritation.
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Human scabies, caused by skin infestation with the arthropod mite, Sarcoptes scabiei, typically results in a papular, intensely pruritic eruption involving the interdigital spaces, and flexure creases. Recent research has led to a reassessment of the morbidity attributable to this parasite in endemic communities, particularly resulting from secondary skin sepsis and postinfective complications including glomerulonephritis. This has led to studies of the benefits of community based control programmes, and to concerns regarding the emergence of drug resistance when such strategies are employed. The renewed research interest into the biology of this infection has resulted in the application of molecular tools. This has established that canine and human scabies populations are genetically distinct, a finding with major implications for the formulation of public health control policies. Further research is needed to increase understanding of drug resistance, and to identify new drug targets and potential vaccine candidates. (+info)
The quality assurance of proficiency testing programs for animal disease diagnostic laboratories.
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Laboratory data credibility has 3 major components: 1) valid methods, 2) proficiency testing (PT) to verify that the analyst can conduct the method and to compare results of other laboratories using the same method, and 3) third-party accreditation to verify that the laboratory is competent to conduct testing and that the method validation has been done within the environment and requirements of an effective quality-management system. Participation in external PT programs by a laboratory is strongly recommended in International Organization for Standardization/International Electrotechnical Commission International Standard 17025. Most laboratory accreditation bodies using this standard require that laboratories participate in such programs to be accredited. Internal PT is also recommended for each analyst. Benchmarking, or comparison between laboratories using PT or reference materials, is also recommended as part of the validation and evaluation of test methods. These requirements emphasize the need for proficiency test providers to demonstrate their competence. Requirements for competence are documented in national and international standards and guidelines, and accreditation is available for providers. This article discusses the activities and the components that are necessary and recommended for PT projects and programs for animal disease diagnostic testing. These are based on the requirements of the national and international standards, which address this subject, and on the experience of the author. The accreditation of external PT programs is also discussed. Organizations that accredit PT providers or that provide PT programs are listed. Existing references, guidelines, and standards that are relevant to PT in veterinary diagnostic laboratories are discussed. (+info)
Cytology of the normal and abnormal choroid plexi in selected domestic mammals, wildlife species, and man.
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A cytologic study of the choroid plexi of animals and humans was carried out using impression smears (imprints, imp) to understand better the cellular changes that occur in the cerebrospinal fluid in the case of disease. The samples, totaling 756 imp were from 11 dogs (239 imp), 10 horses (219 imp), 1 mule (23 imp), 3 cattle (69 imp), 1 sheep (19 imp), 2 pigs (39 imp), 1 deer (20 imp), 4 monkeys (22 imp), and 7 humans (106 imp). The samples came from individuals clinically free of neurologic disease, as well as from a few abnormal cases. Six of the 7 humans had no history of neurologic disease and had a complete necropsy with brain histopathology. The seventh human case had mild neurologic signs at the time of death and only a partial necropsy with histopathological examination of the brain, in which a few small leptomeningeal lymphocytic infiltrates and polymicrogyria were found. One of the human brains without neurologic disease had arteriosclerosis. In the 40 individuals studied, several features and some unique cell types were found, for which little or no information is available. Four different morphologic cell types were consistently found in all the species studied. The first 3 types were arbitrarily named alpha (with deeply basophilic cytoplasm), beta (with neutral to weakly acidophilic cytoplasm), and gamma or vesicle-bearing cells. The third type, gamma, was a cell bearing unique inclusions (vesicles) filled with many tiny light tan to pale pink granules. The fourth type was the Kolmer cell found in very low numbers. Immature lymphocytes were found in all of 3 newborn foals, in 1 pig, and in the only stillborn calf and deer studied. The results suggest that the choroid plexi contain more than 1 epithelial cell type and that knowledge of their morphology is far from complete because other unusual cells and structures are also present in small numbers. Imprints are excellent for studying the choroid plexi, especially for tiny changes that are too subtle to be seen in hematoxylin and eosin sections. (+info)
Natural West Nile virus infection in a captive juvenile Arctic wolf (Canis lupus).
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A case of West Nile virus (WNV) infection in a captive 4-month-old Arctic wolf (Canis lupus) is described. The animal had vomiting, anorexia, and ataxia before death. Histopathology revealed multifocal severe renal lymphoplasmacytic vasculitis, mostly affecting small arterioles, with fibrinoid degeneration of some vessel walls. Many small foci of gliosis were detected in the cerebral cortex. West Nile virus was demonstrated in the kidneys and cerebrum by immunohistochemistry and polymerase chain reaction. The described renal changes represent a novel pathological finding of WNV infection. (+info)
Protein folding pathology in domestic animals.
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Fibrillar proteins form structural elements of cells and the extracellular matrix. Pathological lesions of fibrillar microanatomical structures, or secondary fibrillar changes in globular proteins are well known. A special group concerns histologically amorphous deposits, amyloid. The major characteristics of amyloid are: apple green birefringence after Congo red staining of histological sections, and non-branching 7-10 nm thick fibrils on electron microscopy revealing a high content of cross beta pleated sheets. About 25 different types of amyloid have been characterised. In animals, AA-amyloid is the most frequent type. Other types of amyloid in animals represent: AIAPP (in cats), AApoAI, AApoAII, localised AL-amyloid, amyloid in odontogenic or mammary tumors and amyloid in the brain. In old dogs Abeta and in sheep APrPsc-amyloid can be encountered. AA-amyloidosis is a systemic disorder with a precursor in blood, acute phase serum amyloid A (SAA). In chronic inflammatory processes AA-amyloid can be deposited. A rapid crystallization of SAA to amyloid fibrils on small beta-sheeted fragments, the 'amyloid enhancing factor' (AEF), is known and the AEF has been shown to penetrate the enteric barrier. Amyloid fibrils can aggregate from various precursor proteins in vitro in particular at acidic pH and when proteolytic fragments are formed. Molecular chaperones influence this process. Tissue data point to amyloid fibrillogenesis in lysosomes and near cell surfaces. A comparison can be made of the fibrillogenesis in prion diseases and in enhanced AA-amyloidosis. In the reactive form, acute phase SAA is the supply of the precursor protein, whereas in the prion diseases, cell membrane proteins form a structural source. Abeta-amyloid in brain tissue of aged dogs showing signs of dementia forms a canine counterpart of senile dementia of the Alzheimer type (ccSDAT) in man. Misfolded proteins remain potential food hazards. Developments concerning prevention of amyloidogenesis and therapy of amyloid deposits are shortly commented. (+info)