Epizootiology of an epizootic hemorrhagic disease outbreak in West Virginia

An outbreak of epizootic hemorrhagic disease virus, serotype 2 (EHDV-2) was responsible for localized white-tailed deer (Odocoileus virginianus) mortality in Hardy and Hampshire counties, West Virginia (USA), in the summer and fall of 1993. Using available historical data on regional herd immunity, data opportunistically collected during the epizootic, and postepizootic sampling of hunter-harvested deer, we grossly estimate certain epidemiologic parameters and compare findings to a hypothesis about hemorrhagic disease outbreaks in the Appalachian Mountains. During the epizootic, 57.9 km(2) were actively searched and 228 dead deer were found. Epizootic hemorrhagic disease virus, serotype 2 was isolated from seven of nine deer sampled in Hardy and Hampshire counties. Preepizootic exposure of deer to EHD viruses was unknown, but available data suggest that it was negligible. The geographic distribution of the outbreak was defined by plotting the locations of dead deer found during the outbreak, as well as the locations of deer harvested by hunters after the outbreak that had antibodies to EHDV-2 on a map sectioned into 16.65 km(2) rectangular sections. Sections that included one or more dead deer or hunter-harvested deer with antibodies to EHDV-2 were included in the defined outbreak area. Postoutbreak sampling revealed monospecific EHDV-2 antibodies in 12% of deer harvested by hunters within the defined outbreak area. Based on the available data and accepting certain assumptions, gross calculations suggest that this outbreak appears to have been isolated and probably killed a high percentage of the deer that were infected. This is consistent with the hypothesis that sporadic hemorrhagic disease outbreaks in the Appalachian Mountains are usually localized and severe.     

A naturally occurring epizootic caused by Sendai virus in breeding and aging rodent colonies. I. Infection in the mouse.

An acute Sendai virus epizootic occurred simultaneously in a breeding colony, in experimental and stock animal rooms, and in a colony of aging mice. During the 2-month period that the infection was at its maximum, death rates were approximately doubled. In some strains, the preweanling death rate reached 100%. RFM and BALB/c mice were most susceptible and NZB mice least susceptible. The mortality during the period of Sendai virus infection was increased for most strains and age groups except for the oldest female RFM and NZB mice. Death rates during the epizootic were lowest in young adult mice (greater than 10 weeks of age) and highest in the very young mice (less than 10 weeks of age) and in the oldest male and the moderately aged female mice. Although a substantial number of older mice died during the epizootic, examination of the age-specific death rates indicated that the increase in deaths remained relatively constant for all ages over 10 weeks. This showed that the older mice were not more susceptible to Sendai virus infection. As a sequela of the epizootic, focal chronic pneumonia was found in 10-40% of the mice coming to necropsy even 1 year later.     

Molecular-biologic analysis of avian influenza virus isolates which caused epizootics on the south of West Siberia and in Crimea

The objective of the study was to determine reasons of poultry deaths in Crimea Republic in December 2005 as well as isolation, identification, and comparative analysis of pathogens, which caused epizootics in Siberia and Crimea. During epizootic in poultry in North-East Crimea highly pathogenic avian influenza virus H5N1 was isolated. Phylogenetic analysis of RNA sequences revealed that they belong to one big cluster. Isolated strain was close to viruses, which caused epizootic in July-August 2005 in the south of West Siberia. Conclusion about the high importance of the south of West Siberia in spreading of highly pathogenic influenza viruses H5N1 in Eurasia was made.     

Epizootic situation and measures for control of wild animals' rabies in Republic of Bashkortostan

Epizootologic characteristics of rabies incidence in the Republic of Bashkortostan for the period 1998 - 2006 are presented. Districts of Bashkortostan are divided on 3 zones according to severity of epizootic situation. Three years-cyclicity of rabies incidence with peak during winter was determined. Foxes, raccoons, wolves, lynxes, badgers, minks and, during recent years, corsacs are involved into the epizootic chain. Main source of rabies in the Republic is foxes with share of 91.9% among sick wild animals. During 1999-2006 8 cases of hydrophobia were registered. Results of analysis of effectiveness of oral immunization and regulation of wild fauna population are presented.     

Susceptibility to Fungi of Cotton Boll Worms Before and After a Natural Epizootic of the Entomopathogenic Fungus Nomuraea rileyi (Hyphomycetes)

Epizootics caused by Beauveria bassiana and Nomuraea rileyi have been observed on boll worms and Spodoptera litura in south Indian fields during winter since the last 15 years. During the N. rileyi-induced natural epizootics, some boll worms were found surviving without infection. Whether they represent pathogen-resistant genotypes was investigated. Two insect populations, collected 3 months prior to and during the epizootic were established. Their sensitivity to both the fungi was compared in laboratory bioassays. No significant difference in sensitivity was observed between the two populations. It was concluded that the boll worm population surviving the epizootic was not genotypically resistant.     

Migratory Birds Reinforce Local Circulation of Avian Influenza Viruses

Migratory and resident hosts have been hypothesized to fulfil distinct roles in infectious disease dynamics. However, the contribution of resident and migratory hosts to wildlife infectious disease epidemiology, including that of low pathogenic avian influenza virus (LPAIV) in wild birds, has largely remained unstudied. During an autumn H3 LPAIV epizootic in free-living mallards (Anas platyrhynchos) — a partially migratory species — we identified resident and migratory host populations using stable hydrogen isotope analysis of flight feathers. We investigated the role of migratory and resident hosts separately in the introduction and maintenance of H3 LPAIV during the epizootic. To test this we analysed (i) H3 virus kinship, (ii) temporal patterns in H3 virus prevalence and shedding and (iii) H3-specific antibody prevalence in relation to host migratory strategy. We demonstrate that the H3 LPAIV strain causing the epizootic most likely originated from a single introduction, followed by local clonal expansion. The H3 LPAIV strain was genetically unrelated to H3 LPAIV detected both before and after the epizootic at the study site. During the LPAIV epizootic, migratory mallards were more often infected with H3 LPAIV than residents. Low titres of H3-specific antibodies were detected in only a few residents and migrants. Our results suggest that in this LPAIV epizootic, a single H3 virus was present in resident mallards prior to arrival of migratory mallards followed by a period of virus amplification, importantly associated with the influx of migratory mallards. Thus migrants are suggested to act as local amplifiers rather than the often suggested role as vectors importing novel strains from afar. Our study exemplifies that a multifaceted interdisciplinary approach offers promising opportunities to elucidate the role of migratory and resident hosts in infectious disease dynamics in wildlife.     

Epidemiological survey of Trichinella infection in domestic, synanthropic and sylvatic animals from Argentina

The presence of Trichinella larvae was investigated in 247 samples taken from domestic, synanthropic and sylvatic animals, collected during 1996 to 2005 in 12 endemic provinces of Trichinella infection in Argentina. Muscle larvae of Trichinella from 65 infected animals were identified at the species level by single larva nested polymerase chain reaction (PCR) technique based on the variability within the expansion segment V (ESV) region of the ribosomal DNA. Trichinella infections were found in 97 of 164 pigs, 38 of 56 pork products, two domestic dogs, one domestic cat, 7 of 11 armadillos and 3 of 9 synanthropic rats. All Trichinella isolates were identified as Trichinella spiralis by nested PCR. These findings add new data on the epidemiology of trichinellosis and should be considered when implementing new strategies to control this zoonosis.     

Patterns in the change in the number of carriers and epizootic activity in a floodplain local natural focus of tularemia in Voronezh Province]

Prolonged study of the population of Arvicola terrestris L. in connection with tularemia epizootic among these animals showed this animal to serve as the principal carrier of tularemia infection in the Povorinsk natural focus. Epizootics proved to originate with a definite threshold count of Arvicola terrestris L.; this threshold constituted about 30% of the trapped animals. Dynamics of the epizootic activity was characterized by alterations of cycles of various duration, coursing by waves, with 2--3-year periods. Reduction of the epizootic intensity coursed during a decade in 2 waves with 3-year periods, and during a 7-year period--in one 3-year wave. During the epizootics with the character of a 2-year wave the population of the principal carrier diminished, and with a 3-year wave the count of Arvicola terrestris L. decreased during the first year, and began to increase during the second year, despite the persistence of the epizootic. Detection of regularities attending the changes in the population of the principal carrier of the infection and its connection with the epizootics permitted to make long-period prognoses of the epizootic activity and to plan antiepidemic measures in the focus.     

An epizootic of hemorrhagic disease in white-tailed deer in Missouri

As part of a white-tailed deer (Odocoileus virginianus) survival study in Missouri (USA) we were actively monitoring 97 radio-collared deer when 8 (8%) died. This mortality, which occurred from 20 August to 23 September 1996, consisted of five adult females, two yearling females and one yearling male. Based on the seasonality of this mortality and the isolation of epizootic hemorrhagic disease virus (EHDV) serotype 2 from one of these animals, we believe that these losses resulted from an epizootic of hemorrhagic disease. The remains of five unmarked deer that may have died from HD also were found on the study area during this same period. During the fall following this mortality, we tested serum from 96 deer taken by hunters in the immediate area. Fifteen (16%) were positive for EHDV or bluetongue virus (BTV) antibodies as determined by agar gel immunodiffusion tests. Serum neutralization test results indicated that previous infections were caused by EHDV virus serotype 2. Based on these data, and assuming that there was no prior exposure to EHDV serotype 2 in this population, the exposure rate for this epizootic was 24% of which 8% died. We noted hoof interruptions in only two of the 96 deer sampled. During this mortality event, the Missouri Department of Conservation received no reports of dead deer, and without the radio-monitored animals the event would have been undetected.     

Epizootic characteristic of rabies today

During the 23 year period rabies was registered in the Moscow region in 163 cases among foxes, 22 cases among racoon-like dogs, 92 cases among dogs, 54 cases among cats. In 1991-2000 ten cases of rabies were registered among other wild animal other than foxes and raccoon-like dogs (hares, hedge-hogs, polecats, badgers, hamsters, martens, rats). Under today conditions the generalized epizootological pattern of rabies is characterized by the vector "natural foci-->anthropurgic foci" with wild and domestic animals playing an alternative role in the epizootic process and the circulation of the infective agent. Wild carnivorous animals maintain natural focal infection in time and space, while all domestic animals are a direct or indirect ecological impasse and took no part in the maintenance of the infection. Foxes are the main source of infection for the animals of the anthropurgic cycle: they play a special role in the development of the epizootic situation in the region as the main reservoir and source of the causative agent of rabies as a natural focal infection. Among other wild animals, raccoon-like dogs are involved into epizootic and epidemic chains. Dogs are the main objects to be infected in the anthropurgic cycles, while cats--a progressing group of risk. During the period of 25 years a decrease in the probability of natural rabies was noted.     

Notes on the fleas Xenopsylla vexabilis Jordan, 1925 (Pulicidae: Siphonaptera) in Vietnam as related to the problem of anthropogenic plague foci

In the first half of the XX century, the flea Xenopsylla vexabilis, the main vector of the plague agent in the “natural plague foci” of the Hawaii, was shown to be a specific parasite of the small white-toothed rat Berylmys berdmorei, inhabiting the tropical forests and grasslands of Indochina, including Vietnam. X. vexabilis was not recorded in Vietnamese settlements. This flea was found in the fields bordering natural landscapes and agricultural areas as a parasite of the greater bandicoot rat Bandicota indica, Savile’s bandicoot rat B. savilei, and the rat Rattus koratensis. It was assumed that bandicoot rats may have played an important role in the introduction of the flea to the Pacific islands where X. vexabilis was then established on synanthropic rats. The new data do not support the concept of coevolution of the recent epizootic association Rattus exulans-Xenopsylla vexabilis-Yersinia pestis.     

Seasonality in the infection and invasion of Marteilioides chungmuensis in the Pacific oyster Crassostrea gigas

The protozoan parasite Marteilioides chungmuensis causes irregular enlargement of the ovary in the Pacific oyster Crassostrea gigas. The parasite invades the oyster through the epithelial tissue of the labial palp, replicates in the connective tissue, and then moves to the gonad, producing spores inside the oocytes. In this study the seasonality and invasion period of the parasite into the host was investigated over a 1 yr cycle. Uninfected 1 and 0 yr old (spat) oysters were placed in an epizootic area every month from July 2004 to July 2005 and September 2005 to March 2006, respectively, and left for 1 mo. Labial palps and gonad were sampled monthly and examined for infection by nested PCR and histological observations. Prevalence of infection detected by PCR was 70% or higher from August to October, but declined sharply in November and reached 7% or lower from February to April. To explain the low detection rate in winter, 1 yr old uninfected oysters were placed in an epizootic area in winter (water temperature: 8 to 10 degrees C) for 2 wk and then transferred to M. chungmuensis-free seawater at 24 degrees C. Although prevalence of infection was ca. 7% before transfer to heated seawater, levels of 87% were detected after 1 wk. After a 3 wk exposure to heated seawater, parasites were found in host oocytes by histological observation. It was concluded that the low prevalence in winter was due to insufficient replication of M. chungmuensis at low seawater temperatures, resulting in levels not detectable by nested PCR, and not to the absence of invasion.     

The epidemiological patterns of pseudotuberculosis in Khabarovsk Territory]

Materials on the epidemiological characterization of pseudotuberculosis at the Khabarovsk Territory taken as a whole and in individual settlements, as well as on the evaluation of epizootic situation in natural foci of infection and foci created by human activities, are presented. The results of laboratory studies of vegetables, washings from environmental objects, soil specimens, material taken from rodents are demonstrated and the characterization of the virulent properties of isolated Yersinia pseudotuberculosis strains is given. Two periods (1976-1982 and 1983-1989) were distinguished by their main epidemiological features. The most important feature of the second period is the shift of the seasonal morbidity rise to the middle of summer, which is explained by activation of the mechanism of transmission of this infection due to the supply of early vegetables infected in local vegetable stores. An essential role of wild and synanthropic Muridae as the reservoir of infection is shown; these rodents and the soil maintain the circulation of the infective agent accumulating in the most favorable habitat, vegetable stores. The regularities established in this work contribute to the improvement of epidemiological surveillance.     

Increase in the occurrence of abortions associated with exposure to the Bluetongue virus serotype 8 in naïve dairy herds

The transplacental transmission capacity demonstrated for Bluetongue virus serotype 8 (BTV-8) in cattle probably is associated with an increased occurrence of abortions. The objectives of this study were to quantify the effect of BTV-8 exposure on the occurrence of abortions in previously naive dairy cow herds under natural infection conditions, and to determine a possible risk period during pregnancy associated with this increase. Two criteria were considered in order to estimate the occurrence of abortion: late return-to-service after a first artificial insemination (AI), and short gestations. A late return-to-service was defined as a return taking place 90 to 200 days after a first AI. These criteria were compared between cows in herds exposed during the 2007 epizootic in France and cows in herds that were not exposed. To determine the risk period during a pregnancy, variations in the occurrence of abortions were quantified according to the stage of the pregnancy during which the exposure took place. Survival analyses were used to estimate the risk of increased occurrence of abortion associated with BTV-8 exposure, adjusted by the principal factors known to influence the risk of abortion. Exposure to the BTV-8 virus under natural conditions in previously naive dairy herds notified after clinical suspicion during the 2007 epizootic was associated with an increase in the occurrence of abortions, regardless of the stage of pregnancy. The at-risk gestation period depended on the criteria used to detect abortions. The mean effect of BTV-8 exposure in the ensemble of detected outbreaks corresponded to an increase of 6.7% in late return-to-service. BTV-8 exposure during the first 3 mo of gestation was associated with a 15% increase in late return-to-service for cows with no return-to-service at 90 days, while this increase was 6% for exposure starting from the third month of gestation (in outbreaks detected in September). BTV-8 exposure from the third month of gestation was associated with a 1.9% increase of short gestations. The effect of exposure was more pronounced for outbreaks detected early in the epizootic compared with those detected later.     

Scuticociliate infection and pathology in cultured turbot Scophthalmus maximus from the north of Portugal

During the years 2004 and 2005 high mortalities in turbot Scophthalmus maximus (L.) from a fish farm in the north of Portugal were observed. Moribund fish showed darkening of the ventral skin, reddening of the fin bases and distended abdominal cavities caused by the accumulation of ascitic fluid. Ciliates were detected in fresh mounts from skin, gill and ascitic fluid. Histological examination revealed hyperplasia and necrosis of the gills, epidermis, dermis and muscular tissue. An inflammatory response was never observed. The ciliates were not identified to species level, but the morphological characteristics revealed by light and electronic scanning microscopes indicated that these ciliates belonged to the order Philasterida. To our knowledge this is the first report of the occurrence of epizootic disease outbreaks caused by scuticociliates in marine fish farms in Portugal.     

Ecological Aspects of Evolution of the Plague Microbe Yersinia pestis and the Genesis of Natural Foci

A new hypothesis of the origin of the plague microbe in the Mongolian bobak (Marmota sibirica Radde, 1862) populations in Central Asia during the Pleistocene is based on the ideas of its relative phylogenetic recency. The Late Pleistocene cooling, which induced a deep freezing of the grounds in southern Siberia, Mongolia, and Manchuria, is considered as an inducer of speciation. The main ecological factors of the plague microbe evolution include the species specific behavior of the Mongolian bobak as it prepared to hibernate related to its occurrence in arid petrophytic landscapes and the larval parasitism of the flea Oropsylla silantiewi Wagn., 1898 in winter. Genesis of the plague foci is divided into two periods: natural-historical and biosocial. During the first period, the primary natural foci in Eurasia were formed and, during the second period, synanthropic (rat) and secondary natural foci appeared with the participation of humans in Africa, The New World, and on some tropical islands.     

Molecular characterization of epizootic hemorrhagic disease virus serotype 1 associated with a 1999 epizootic in white-tailed deer in the eastern United States

During the autumn of 1999 (mid-August-late September), an outbreak of hemorrhagic disease in white-tailed deer (Odocoileus virginianus) caused by epizootic hemorrhagic disease virus serotype 1 (EHDV-1) occurred along the east coast of the United States from Georgia to New Jersey. An EHDV-1 epizootic of such magnitude had not been described in this region since 1975. To determine the genetic relatedness among the 1999 viruses, as well as among additional EHDV-1 isolates from the eastern and western United States, portions of the S10 and L2 gene segments were sequenced and compared utilizing phylogenetic analyses. Nearly all of the 1999 eastern isolates were identical in nucleotide sequence at one or both loci. Additionally, confirmed cases of EHDV-1 in white-tailed deer occurred in a south (Georgia)-to-north (New Jersey/Virginia) progression over a short period of approximately six weeks. Taken together, these results indicate that this outbreak resulted from the spread of a single viral strain. The phylograms derived from analysis of the entire sample set displayed eastern and western region-specific clusterings (topotypes), as well as an eastern versus western difference in branch lengths, which may reflect the influence of epizootic versus enzootic transmission patterns on viral genetic diversity.     

The prediction of the activity of anthrax foci in Voronezh Province

During the period of 1959-1985 the activity of the foci of anthrax in Voronezh Province was found to be related to the state of some meteorological factors in the previous year and the number of murine [correction of myomorphous] rodents in hayricks and stacks of straw in early spring of the current year, this relationship being stable and statistically significant. Multiple regression equations permitting the annual quantitative prognostication of the intensity of the epizootic and epidemic situations were worked out.     

Bluetongue in free-ranging pronghorn antelope (Antilocapra americana) in Wyoming: 1976 and 1984

At least 3,200 pronghorn (Antilocapra americana) died during a bluetongue (BT) epizootic in eastern Wyoming during late September and early October 1976. In August and September 1984, another BT epizootic occurred in northeastern Wyoming resulting in 300 known pronghorn deaths. In 17 pronghorn examined postmortem, hemorrhages and edema were the most common gross pathologic changes. Microscopic changes included hemorrhage, edema, arterial fibrinoid necrosis, lymphoid depletion in splenic and lymphatic follicles, and neuronal necrosis. Bluetongue virus serotype 17 was isolated from pronghorn in both epizootics. Mortalities ceased with the advent of cool weather in late September and October. Seventy-six of 94 pronghorn killed by hunters during the latter period of the 1976 epizootic, and 14 of 24 pronghorn killed 1 yr later had serologic evidence of exposure to BT virus. The reproductive rate in pronghorn was depressed to 47 fawns per 100 does in August 1977, but returned to 93 fawns per 100 does by 1978. Following the 1984 outbreak, the reproductive rate was similarly depressed, but the cause was confounded by other environmental and range conditions. Deer, mostly mule deer (Odocoileus hemionus), also died during both epizootics of what was presumed to be BT.     

Prevalence and implications of feline coronavirus infections of captive and free-ranging cheetahs (Acinonyx jubatus).

The extent and progression of exposure to feline infectious peritonitis (FIP) virus in the cheetah, Acinonyx jubatus, was monitored by a world-wide serological survey with indirect fluorescent antibody titers to coronavirus. The indirect fluorescent antibody assay was validated by Western blots, which showed that all indirect fluorescent antibody-positive cheetah sera detected both domestic cat and cheetah coronavirus structural proteins. There was a poor correlation between indirect fluorescent antibody results and the presence of coronaviruslike particles in cheetah feces, suggesting that electron microscopic detection of shed particles may not be an easily interpreted diagnostic parameter for FIP disease. Low, but verifiable (by Western blots [immunoblots]) antibody titers against coronavirus were detected in eight free-ranging cheetahs from east Africa as well as from captive cheetahs throughout the world. Of 20 North American cheetah facilities screened, 9 had cheetahs with measurable antibodies to feline coronavirus. Five facilities showed patterns of an ongoing epizootic. Retrospective FIP virus titers of an FIP outbreak in a cheetah-breeding facility in Oregon were monitored over a 5-year period and are interpreted here in terms of clinical disease progression. During that outbreak the morbidity was over 90% and the mortality was 60%, far greater than any previously reported epizootic of FIP in any cat species. Age of infection was a significant risk factor in this epizootic, with infants (less than 3 months old) displaying significantly higher risk for mortality than subadults or adults. Based upon these observations, empirical generalizations are drawn which address epidemiologic concerns for cheetahs in the context of this lethal infectious agent.