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.

Prevalence of reovirus-specific antibodies in young children in Nashville, Tennessee

Although reovirus infections are thought to be common in adults, there have been few assessments of the seroprevalence of reovirus in young children. We developed an indirect enzyme-linked immunosorbent assay to measure levels of total antireovirus immunoglobulin A, G, and M in serum specimens collected from otherwise healthy infants and children (1 month to 5 years of age) in Nashville, Tennessee. Of the 272 serum specimens evaluated, 64 (23.5%) tested positive for reovirus-specific antibodies. We observed an age-dependent increase in reovirus-specific antibodies in children 1 year of age and older, peaking at 50.0% in children 5–6 years of age. These findings suggest that reovirus infections are common during early childhood

Genetic variation among epizootic hemorrhagic disease viruses in the southeastern United States: 1978–2001

The epizootic hemorrhagic disease (EHD) viruses, which are endemic in the southeastern United States, are the causative agents of an important clinical disease in wild and captive ruminants. In order to elucidate the molecular epidemiology of EHD serotype 2, the sequences of portions of the S10 and L2 gene segments (which encode the NS3 viral egress protein and the VP2 surface protein, respectively) of viral isolates made from white-tailed deer over 23 years(1978-2001) were determined and compared using phylogenetic analyses. Both loci demonstrated very little genetic variation among isolates, with a 94-100% nucleotide identity among isolates at the S10 locus (98-100% amino acid conservation), and an 89.1-100% identity among isolates at the L2 locus (87.6-100% amino acid conservation). The grouping of isolates within the resulting cladograms appeared nearly random with respect to time of isolation and geographic origin. One exception to this was a distinctive grouping of some isolates from 1996 to 1997, which formed a separate subclade in both the S10 and L2 cladograms.

Hemorrhagic disease in Kansas: enzootic stability meets epizootic disease

Kansas (USA) could represent a transition area between contrasting epidemiologic patterns of hemorrhagic disease (HD) in the midwestern United States. In this study, we compare the distribution of reported clinical HD with serologic data to determine whether the risk of HD in white-tailed deer (Odocoileus virginianus) is associated with geographic location corresponding to the reported distribution of two white-tailed deer subspecies. On the basis of a high prevalence of antibodies (91-100%) to multiple serotypes of epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV), with correspondingly few reports of clinical HD, it appears that a state of enzootic stability exists in central and western Kansas. This area corresponds to the reported range of O. virginianus texanus. In contrast, in the eastern third of the state, which corresponds to the reported range of O. virginianus macronurus, antibody prevalence is significantly lower (45%), EHDV serotypes appear to predominate, and HD, as confirmed by virus isolation, has been consistently reported. These results suggest an abrupt demarcation between enzootic stability in central and western Kansas to a pattern of epizootic HD within the eastern part of this state. Understanding host, vector, and environmental variables responsible for these contrasting patterns could have application to understanding the risk of HD in the midwestern United States.

Epizootiology of hemorrhagic disease in mule deer in central Arizona

We report two male mule deer (Odocoileus hemionus) mortalities that occurred near Prescott, Arizona (USA) in September 2001. Necropsy lesions were compatible with those described for hemorrhagic disease (HD). Bluetongue (BTV) and epizootic hemorrhagic disease (EHDV) viral RNA were identified in tissues from one deer and EHDV viral RNA was identified in the other via reverse transcription-polymerase chain reaction (RT-PCR). Virus isolation attempts were unsuccessful in both cases. To determine geographic range and viral serotypes involved, we collected blood samples from healthy hunter-harvested male mule deer in three game management units near Prescott in October 2001. Forty-one blood samples were collected and antibodies against EHDV and/or BTV were found in 21/41 (51%) samples as determined by agar immunodiffusion. Serum neutralization test results suggest that multiple EHDV and BTV serotypes are present in Arizona.

Recombinant VP6-based enzyme-linked immunosorbent assay for detection of immunoglobulin G antibodies to Eyach virus (genus Coltivirus)

BACKGROUND

Eyach virus (EYAV) is a tick-borne virus belonging to genus Coltivirus, family Reoviridae. It was isolated in Germany and France and has been suspected to be responsible for neurological diseases in humans. To date, there has been no relatively rapid and relatively specific serological assay for EYAV.

OBJECTIVES

To develop an ELISA for EYAV, suitable for epidemiological and/or diagnostic purposes. This ELISA should allow to distinguish between infections with EYAV and the related Colorado tick fever virus (CTFV).

STUDY DESIGN

VP6, VP7 and VP12 of Eyach virus (the three proteins most divergent between EYAV and CTFV) were expressed in bacteria using the pGEX-4T-2 vector. A partial sequence of VP6 (designated pVP6) was chosen to develop an ELISA for detecting anti-EYAV IgG antibodies in serum. This choice was based on two observations: (i) the homologous VP7 protein of CTFV was successfully used as a target for detecting antibodies to CTFV (the VP7 showed the highest reactivity to an anti-CTFV antibody among all CTFV expressed proteins); (ii) to distinguish infection with EYAV from a CTFV infection: the expressed sequence was chosen within a region which is highly divergent (49% of amino acid identity) from the homologous VP7 sequence of CTFV.

RESULTS AND CONCLUSIONS

pVP6 was shown to be the most reactive among the three expressed proteins. The elaborated pVP6 ELISA was evaluated with 340 sera of French blood donors, and found to exhibit a specificity of 100% (no false positives). Furthermore, no cross reaction was detected with antibody to CTFV, thus permitting us to distinguish between infections by either virus. The use of this recombinant protein for serological assays is a good alternative to the use of native EYAV antigen due to the extremely low productivity of the virus in cell culture, and the requirement for suckling mice. This ELISA will be useful to clarify the epidemiological status and the suspected pathogenicity of the virus.

Recombinant VP9-based enzyme-linked immunosorbent assay for detection of immunoglobulin G antibodies to Banna virus (genus Seadornavirus)

Banna virus (BAV, genus Seadornavirus, family Reoviridae) is an arbovirus suspected to be responsible for encephalitis in humans. Two genotypes of this virus are distinguishable: A (Chinese isolate, BAV-Ch) and B (Indonesian isolate, BAV-In6969) which exhibit only 41% amino-acid identity in the sequence of their VP9. The VP7 to VP12 of BAV-Ch and VP9 of BAV-In6969 were expressed in bacteria using pGEX-4T-2 vector. VP9 was chosen to establish an ELISA for BAV, based mainly on two observations: (i). VP9 is a major protein in virus-infected cells and is a capsid protein (ii). among all the proteins expressed, VP9 was obtained in high amount and showed the highest immuno-reactivity to anti-BAV ascitic fluid. The VP9s ELISA was evaluated in three populations: French blood donors and two populations (blood donors and patients with a neurological syndrome) from Malaysia, representing the region where the virus was isolated in the past. The specificity of this ELISA was >98%. In mice injected with live BAV, the assay detected IgG-antibody to BAV infection 21 days post-injection, which was confirmed by Western blot using BAV-infected cells. The VP9 ELISA permits to determine the sero-status of a population without special safety precautions and without any requirements to propagate the BAV. This test should be a useful tool for epidemiological survey of BAV.

Differences in Ibaraki virus RNA segment 3 sequences from three epidemics

Phylogenetic tree and partial nucleotide sequence analysis of RNA segment 3 were conducted to compare the Ibaraki virus (IBAV) strains from three epidemics in Japan, and serotype 2 epizootic hemorrhagic disease virus strains isolated in Australia, Taiwan, and Canada. Each strain was classified relative to the Ibaraki disease (IBAD) epidemics, which occurred in 1959-1960, 1987, or 1997-1998. In particular, major variation of the gene was identified in the strains isolated after 1997 when a new type of IBAD with the abnormal birth was confirmed. Ibaraki viruses isolated in Japan were more closely related to Taiwanese and Australian strains based on genetics, while the Canadian strain was more distantly related.

Reovirus identified as cause of disease in young geese

The pathology, epizootiology and aetiology of a specific disease of young geese, which has been seen in Hungary for more than three decades, were investigated. The disease was characterised by splenitis and hepatitis with miliary necrotic foci during the acute phase, and epicarditis, arthritis and tenosynovitis during the subacute/chronic phase. Clinical signs usually appeared at 2 to 3 weeks of age and persisted for 3 to 6 weeks. From different organs of the affected birds, a reovirus was isolated in embryonated eggs and tissue cultures of Muscovy duck or goose origin, as well as in Vero cells. In experimental infections, the dominant features of the disease were reproduced in day-old and young goslings. The biological and partial molecular characterisation of one of the isolated strains (D15/99) showed that it was related to the reovirus described as the cause of a similar disease of Muscovy ducks. An RT-PCR method suitable for the detection of reoviruses was also elaborated and tested. This is the first report on the involvement of reovirus in arthritis of geese.

Paramyxovirus and reovirus infections in wild-caught Mexican lizards (Xenosaurus and Abronia spp.)

Virus isolation attempts were carried out on wild-caught Xenosaurus grandis, X. platyceps, and Abronia graminea from Mexico. These animals were also tested for exposure to paramyxoviruses and reoviruses. Pharyngeal and cloacal swabs were collected from 30 lizards, and blood was collected from 23 lizards. A cytopathogenic virus was isolated from the cloacal swab of one of the X. platyceps. The isolate was identified as a paramyxovirus on the basis of its sensitivity to chloroform, resistance to 5-iodo-2'-deoxyuridine, size and morphology of the viral particles, hemagglutination of chicken erythrocytes, and serologic reaction with paramyxovirus-specific antisera. Antibodies against the paramyxovirus isolated in this study were found in four animals from three species. Antibodies against a different paramyxovirus isolated from a monitor lizard were found in seven animals from three species, showing that all the species tested are susceptible to paramyxovirus infections. Antibodies to a reptilian reovirus were found in three of the X. grandis.

Twenty year study of the occurrence of reovirus infection in hospitalized children with acute gastroenteritis in Argentina

We studied the occurrence of reovirus infection in children hospitalized with acute gastroenteritis in Argentina during a 20-year interval (1981 through 2001). Three of 2854 (0.10%) stools were positive for reovirus but negative for adenovirus, astrovirus and rotavirus. Children infected with reovirus were <1 year old; one had meningoencephalitis in addition to gastroenteritis. This study indicates that reovirus is an uncommon cause of childhood gastroenteritis requires medical assistance.

Reovirus infection in psittacine birds (Psittacus erithacus): morphologic and immunohistochemical study

In this paper we report on an outbreak of reovirus, herpesvirus (Pacheco disease), and/or mycosis infection (Aspergillus spp. and Zygomyces spp.) affecting a batch of young African grey parrots (Psittacus erithacus), with 80% morbidity and 30% mortality. Study material was taken from five birds (four dead and one euthanatized) with a range of clinical symptoms (depression, diarrhea, respiratory symptoms). Diagnosis was confirmed by immunohistochemical detection of avian reovirus, electron microscopy, and virus isolation. Viral antigen of reovirus was detected mainly in large mononuclear cells in the bursa of Fabricius and the spleen, pancreas epithelial cells, and circulating cells; lymphoid organs displayed the largest number of immunopositive cells and severe lymphocyte depletion. Bacteriologic study was negative. Reovirus infection was common in all birds studied, whereas Pacheco disease and mycosis were found in only some, suggesting that reovirus could be the initial cause triggering the outbreak and facilitating infection by other agents and their swift spread through the batch.

Isolation and characterization of a reovirus from common eiders (Somateria mollissima) from Finland

Samples of brain, intestine, liver, lung, spleen, and bursa of Fabricius were collected from five common eider (Somateria mollissima) duckling carcasses during a die-off in the western Gulf of Finland (59 degrees 50'N, 23 degrees 15'E) in June 1996. No viral activity was observed in specific-pathogen-free chicken embryos inoculated with tissue suspensions, but samples of bursa of Fabricius from three birds were positive when inoculated into Muscovy duck (Cairina moschata) embryo fibroblasts. The isolates were characterized as nonenveloped RNA viruses and possessed several characteristics of the genus Orthoreovirus. Virus particles were icosahedral with a mean diameter of 72 nm and were stable at pH 3.0; their genome was separated into 10 segments by polyacrylamide gel electrophoresis. Mallard (Anas platyrhynchos) ducklings experimentally infected with the eider reovirus showed elevated serum activities of aspartate aminotransferase, creatine kinase, and lactate dehydrogenase enzymes and focal hemorrhages in the liver, spleen, and bursa of Fabricius. During 1997-99, the prevalence of neutralizing antibodies to the isolated virus ranged from 0 to 86% in 302 serum samples collected from incubating eider hens at three nesting areas along coastal Finland. The highest seroprevalence was found in Hanko in 1999, just weeks before reports of an uninvestigated mortality event resulting in the death of an estimated 98% of ducklings at that location. These findings raise the question of potential involvement of the virus in poor duckling survival and eider population declines observed in several breeding areas along coastal Finland since the mid-1980s.

The classification of seven serotypes of equine encephalosis virus and the prevalence of homologous antibody in horses in South Africa

Selected isolates of equine encephalosis virus were shown to have comparable viral protein profiles and to represent seven distinct serotypes, based on cross-neutralization tests. Serotype-specific virus-neutralizing antibody in serum samples from horses confirmed the widespread occurrence of infection. The distribution and prevalence of individual serotypes however, varied considerably. Localised foci with an increased seasonal seroconversion in groups of horses to a specific serotype and the detection of an ongoing low level of infection from other serotypes within the population, confirmed the independent persistence of the viruses in a maintenance cycle. The identification of donors with antibody resulting from infection with multiple serotypes indicated a low level of cross-protection in horses to natural reinfection.

Hemorrhagic disease in bighorn sheep in Arizona

Two bighorn sheep from Arizona (USA) were submitted for necropsy. One was a Rocky Mountain bighorn (Ovis canadensis canadensis) and the other was a desert bighorn (Ovis canadensis mexicana). Both had lesions consistent with those of hemorrhagic disease (HD). Epizootic hemorrhagic disease virus (EHDV) type-2 and bluetongue virus (BTV) type-17, respectively, were isolated from the sheep tissues. To our knowledge, HD caused by either EHDV or BTV infection has not been documented previously in Arizona bighorn sheep.

Hemorrhagic disease in deer in Arizona

Two mule deer (Odocoileus hemionus) and one white-tailed deer (Odocoileus virginianus) in Arizona (USA) were submitted for necropsy. Gross and microscopic lesions compatible with hemorrhagic disease (HD) were observed in all three deer. Epizootic hemorrhagic disease virus type 2 (EHDV-2) was isolated from two of the deer. To our knowledge, this is the first documentation of HD in deer in Arizona. Two of the mortalities were attributed to EHDV-2 infection.

Incursion of epizootic hemorrhagic disease into the Okanagan Valley, British Columbia in 1999

In September 1999, unusually high mortality rates in white-tailed deer and California bighorn sheep occurred in the southern Okanagan Valley. Necropsy and histopathologic findings were compatible with epizootic hemorrhagic disease (EHD); the presence of virus was not demonstrated. Subsequent serologic and polymerase chain reaction assays on sentinel cattle suggested an EHD virus incursion.

Absence of a genetic bottleneck in a wild rabbit (Oryctolagus cuniculus) population exposed to a severe viral epizootic

Infectious diseases and their demographic consequences are thought to influence the genetic diversity of populations. In Europe, during the last 50 years, the European rabbit (Oryctolagus cuniculus) has suffered two important viral epizootics: myxomatosis and rabbit viral haemorraghic disease (RVHD). Although mortality rates were very high, the impact of these diseases on genetic diversity has never been assessed directly. The subject of this paper is a wild rabbit population in France, which has been studied since the beginning of the 1980s. The first outbreak of RVHD occurred in 1995 and provoked a demographic crash. The population, sampled for the first time in 1982 and 1994, was sampled again at the end of 1996 to examine the impact of the epizootic on genetic diversity. In spite of the observed high mortality rate ( approximately 90%), analysis of 14 polymorphic loci (allozymes and microsatellites) showed no loss in genetic diversity after the epizootic. Determination of temporal changes in allele frequencies indicated that the population evolved under genetic drift. The temporal method of Waples demonstrated a significant decrease in the effective population size (Ne) correlated with the demographic crash due to the epizootic. However, the population had only been studied for two generations after the epizootic and the remnant population size probably stayed high enough ( approximately 50 individuals) to keep its genetic diversity at the precrash level. These results suggest that, contrary to what is usually thought and in spite of the subsequent high mortality rates, past epizootics (especially myxomatosis) may have had little effect on the genetic diversity of wild rabbit populations in Europe.

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.

Definition of Ross River virus vectors at Maroochy Shire, Australia

Evidence of Ross River (RR) virus infection in field-collected mosquitoes and data from laboratory vector competence experiments incriminated a range of mosquito species as important vectors of RR virus in Maroochy Shire, Queensland, Australia. Nine RR and 2 Barmah Forest virus isolates were recovered from 27,529 mosquitoes collected in light traps from Maroochy Shire during 1996. Nine of the 10 most abundant mosquito species collected in light traps were fed on blood containing the B94/20 strain RR isolated from Queensland in 1994. All species except for Culex sitiens Wiedemann were susceptible to experimental infection. Evidence of RR virus transmission to mice was found with Aedes vigilax (Skuse), Aedes funereus (Theobald), Aedes procax (Skuse), Culex annulirostris Skuse, Mansonia uniformis (Theobald) and Culex australicus Dobrotworsky & Drummond. Aedes notoscriptus (Skuse) and Aedes multiplex (Theobald) were susceptible to RR virus infection, although there was no evidence of virus transmission. Based on adult abundance and vector competence results, freshwater species such as Cx. annulirostris, Ae. procax, and Ae. funereus, and saltmarsh Ae. vigilax, appear to be important vectors of RR virus in Maroochy Shire and control programs should be revised to include these species.

Serosurvey for selected disease agents in white-tailed deer from Mexico

Serum samples from 350 white-tailed deer (Odocoileus virginianus texanus) collected in March 1994 from northeastern Mexico were tested for the prevalence of antibody activity against five infectious diseases of ruminants. The prevalence rate was 81% for bluetongue virus (BTV) of all serotypes, 72% for epizootic hemorrhagic disease virus (EHDV), 3% for Borrelia burgdorferi, 69% for Anaplasma marginale, and 0% for Brucella abortus, B. melitensis, and B. ovis. These are diseases that affect domestic ruminants, and deer may act as a reservoir of infection. In addition, if deer are translocated, they may introduce pathogens to formerly disease-free areas. The high seroprevalence of BTV and EHDV cannot be related to the presence of hemorrhagic disease in the deer in this region. This is the first report to indicate the presence of B. burgdorferi infection of deer in Mexico. Despite the high prevalence of A. marginale titers, it is uncertain that deer play a role in the epizootiology of cattle anaplasmosis in the region. Apparently, white-tailed deer are unimportant in the epizootiology of brucellosis of both cattle and goats in northeastern Mexico.

Epidemic of blindness in kangaroos--evidence of a viral aetiology

OBJECTIVE

To determine the cause of an epidemic of blindness in kangaroos.

DESIGN AND PROCEDURES

Laboratory examinations were made of eyes and brains of a large number of kangaroos using serological, virological, histopathological, electron microscopical, immunohistochemical methods, and PCR with cDNA sequencing. In addition, potential insect viral vectors identified during the disease outbreak were examined for specific viral genomic sequences.

SAMPLE POPULATION

For histopathological analysis, 55 apparently blind and 18 apparently normal wild kangaroos and wallabies were obtained from New South Wales, Victoria, South Australia, and Western Australia. A total of 437 wild kangaroos and wallabies (including 23 animals with apparent blindness) were examined serologically.

RESULTS

Orbiviruses of the Wallal and Warrego serogroups were isolated from kangaroos affected with blindness in a major epidemic in south-eastern Australia in 1994 and 1995 and extending to Western Australia in 1995/96. Histopathological examinations showed severe degeneration and inflammation in the eyes, and mild inflammation in the brains. In affected retinas, Wallal virus antigen was detected by immunohistochemical analysis and orbiviruses were seen in electron microscopy. There was serological variation in the newly isolated Wallal virus from archival Wallal virus that had been isolated in northern Australia. There were also variations of up to 20% in genotype sequence from the reference archival virus. Polymerase chain reactions showed that Wallal virus was present during the epidemic in three species of midges, Culicoides austropalpalis, C dycei and C marksi. Wallal virus nucleic acid was also detected by PCR in a paraffin-embedded retina taken from a blind kangaroo in 1975.

CONCLUSION

Wallal virus and perhaps also Warrego virus are the cause of the outbreak of blindness in kangaroos. Other viruses may also be involved, but the evidence in this paper indicates a variant of Wallal virus, an orbivirus transmitted by midges, has the strongest aetiological association, and immunohistochemical analysis implicates it as the most damaging factor in the affected eyes.