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.

Reovirus serology in broiler parents and their progeny and its correlation with performance

An intensive vertically integrated monitoring program for broiler breeders and their offspring was set up in a Belgian poultry integration between 1993 and 1997. Serology for anti-reovirus antibodies was performed by enzyme-linked immunosorbent assay on blood samples taken from the broiler parents throughout rearing and production and also on blood samples taken at day-old and at slaughter from the broilers. Furthermore, production parameters of the birds were registered. All data were used two by two in a simple correlation study to calculate the degree to which these variables were linearly correlated. The reovirus antibody pattern indicated frequent field infections breaking through vaccinal immunity in the broiler parents. Under the epidemiologic conditions of this study, high antibody titers in the parents or in the broilers at day-old were significantly correlated with poor feed conversion, increased mortality, increased slaughterhouse condemnation, and low production score in the broilers. These correlations strongly support the view that reovirus infections can be economically important under European conditions of broiler production. Improvement of reovirus vaccines or the vaccination scheme in broiler parents or both may lead to better production results in the broiler offspring.

[Reovirus infection of pheasants (Phasianus colchicus)]

In this case report we discribe clinic, pathology and diagnostic of an avian reovirus-infection in pheasants. The disease was observed 1993 in a flock of game-pheasants in the western part of Turkey. Of a live-stock of 100 animals, 27 were affected most of them being three to five months old. Beside a general disorder, sick pheasants showed signs of shortness of breath as well as greenish, watery diarrhoea and died within a week. The pathologic findings were dominated by an extreme hepatopathia. In addition a fibrinous tracheitis, a catarrhal inflammation of the gut and a perihepatitis fibrinosa could be observed. From organs of affected pheasants a pathogen could be isolated, which was characterized anti-genetically, by physico-chemical properties an by electronmicroscopy as avian reovirus.

Paramyxoviral and reoviral infections of iguanas on Honduran Islands

Thirty-five free-ranging healthy spiny-tailed iguanas (31 Ctenosaura bakeri, 4 C. similis) and 14 green iguanas (Iguana iguana rhinolopha) were caught and held in captivity for 2 days. Blood was collected from all animals and their sera were evaluated for antibody titres against reptilian reoviruses, reptilian paramyxoviruses, and avian paramyxovirus-1 (PMV-1). Cloacal and pharyngeal swabs also were collected and examined for viral content by incubation on chicken embryo fibroblasts (CEF) and terrapene heart cells (TH-1). No virus was isolated from the pharyngeal and cloacal swabs on CEF and TH-1. Twenty-three (47%) of 49 sera samples tested positive for reptilian reoviruses by virus neutralization tests. Twenty (41%) of 49 samples had antibodies against one reptilian PMV isolate by virus neutralization tests and 3 (9%) of 34 by hemagglutination inhibition tests. No antibodies were detected against the other PMV isolate of reptilian origin nor against avian PMV-1. This is the first description of serum antibodies against reptilian reoviruses and PMV in wild iguanas.

Major viral diseases affecting fish aquaculture in Spain

The number of viruses isolated from fish has grown in the last few years as a reflection of the increasing interest in fish diseases, particularly those occurring in aquaculture facilities. Of all the described viruses, only a few are considered to be of serious concern and economic importance; they are described in this review, drawing special attention to the four families of viruses (Birnaviridae, Rhabdoviridae, Iridoviridae and Reoviridae) that have been reported in Spanish aquaculture. Infectious pancreatic necrosis virus, a member of the first family, is the most spread virus with a prevalence of 39%. Viral diseases are untreatable and because effective and safe vaccines for fish are not yet commercially available, a great care needs to be exercised when moving fish or eggs from one site or country to another. Some fish health control regulations have been legislated in Europe and USA.

Application of molecular biological techniques for detection of epizootic hemorrhagic disease virus (EHDV-318) recovered from a sentinel calf in central Sudan

Epizootic hemorrhagic disease virus (EHDV), isolate 318 (EHDV-318), an untyped virus recovered from a sentinel calf herd at the Khartoum University farm in central Sudan, was characterized using molecular biological techniques. With dot blot hybridization technique, a cDNA probe derived from genome segment 6 of EHDV-2 (Alberta strain) hybridized with RNA from EHDV-318. Application of serogroup-specific EHDV polymerase chain reaction (PCR) to EHDV-318 RNA resulted in specific amplification of a 387 bp PCR product. Amplification product was visualized on ethidium bromide-stained agarose gel. Specificity of the PCR products was confirmed by chemiluminescent hybridization with a non-radiolabelled internal probe. No amplification product or hybridization signal was detected when the serotype-specific EHDV-1 or EHDV-2 PCR-based assays were applied to RNA from EHDV-318. The scientific data presented in this study indicated that cDNA probes and serogroup-specific PCR-based assay can be used to classify the virus as a member of EHDV serogroup, and as serotypically distinct from EHDV-1 and EHDV-2.

Hemorrhagic disease in white-tailed deer in Texas: a case for enzootic stability

Although antibodies to viruses in both the epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) sero-groups have been reported from white-tailed deer (Odocoileus virginianus) in Texas (USA), there are few reports of hemorrhagic disease (HD) in these populations. To understand the extent and diversity of exposure to the North American EHDV and BTV serotypes in these deer populations, we serologically tested 685 white-tailed deer collected from November 1991 through March 1992 throughout their range in Texas. Overall, 574 (84%) of deer had antibodies to EHDV or BTV. Prevalence estimates varied according to ecological region, from 57% in the Gulf Prairies to 100% in the northwest Edwards Plateau. Based on serum neutralization tests, the deer had evidence of previous exposures to multiple EHDV and BTV serotypes, with evidence of exposure to two to five serotypes detected in each ecological region. The apparent lack of HD in relation to this high antibody prevalence cannot be explained, but may be related to enzootic stability in which a near perfect host-virus relationship exists.

Monitoring of Culicoides spp. at a site enzootic for hemorrhagic disease in white-tailed deer in Georgia, USA

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) were monitored at a Georgia (USA) site where epizootic hemorrhagic disease (EHD) and bluetongue (BT) viruses are enzootic among white-tailed deer (Odocoileus virginianus). Collections were made using a captive white-tailed deer and light traps from June 1993 through November 1994. We collected 210,482 females from the captive deer during morning and evening periods. Predominant species were C. lahillei (73%), C. stellifer (16%), C. biguttatus (6%), C. niger (3%), C. spinosus (2%), and C. paraensis (0.2%). Other species were C. venustus, C. obsoletus/sanguisuga, C. haematopotus, C. guttipennis, and C. arboricola, which together represented < 0.1% of the specimens collected. No C. variipennis, a known vector of EHD and BT viruses, were collected from the deer. An estimated 953,299 females were collected in 695 light-trap nights. The most common species in light-trap collections were C. spinosus (45%), C. biguttatus (27%) and C. stellifer (24%). Culicoides variipennis was rare in the light-trap samples, representing < 0.01% of the total collections. There was serological evidence from hunter-killed deer that local deer were infected with EHD and BT viruses during the study, particularly during 1994. A primary suspect vector was C. lahillei, which attacked the bait deer in large numbers during the summer and early fall of both 1993 and 1994. Based on their seasonality, relative abundance, and host-seeking activity, C. stellifer and C. spinosus also were considered as possible vectors. However, virus isolation attempts on 113,716 Culicoides, including 62,530 C. lahillei and 32,769 C. stellifer, were negative.

Development of PCR-based tests for the identification of North American isolates of epizootic haemorrhagic disease virus

A serogroup-specific polymerase chain reaction (PCR) assay and isolate identification strategies (restriction endonuclease analysis (REA) and nucleotide sequencing) were developed for the detection of North American isolates of epizootic haemorrhagic disease virus (EHDV). PCR primers (EHDV-pr4, EHDV-pr5) were designed to hybridize to the L3 gene of a North American isolate of EHDV serotype 1. Total nucleic acid was extracted from preparations of infected tissue culture and PCR was performed using a cDNA-PCR kit, according to the manufacturer's specifications. The PCR assay generated a 459 base pair product from North American isolates of EHDV serotypes 1 and 2, while bluetongue virus (BTV) serotypes 10, 11, 13, and 17, and cell controls, failed to demonstrate PCR products. Slight modifications allowed for the PCR detection of EHDV-1 and -2 in white-tailed deer blood (Odocoileus virginiatus); PCR fragments were not amplified from uninfected deer blood. A number of restriction endonucleases and sequencing primers were evaluated for their utility in isolate identification experiments. Specifically, REA employing HincII and cycle sequencing with an internal primer (EHDV-1-pr3) proved most successful for identifying isolate-specific genome markers. The techniques presented are expected to prove valuable for rapid and specific detection of possible future EHDV incursions in wild and domestic animal species.

Arboviruses causing neurological disorders in the central nervous system

Arthropod-borne viruses are important causes of diseases of the central nervous system. In addition to the tick-borne encephalitis viruses, other arboviruses in Europe are known to cause neurological disorders. Among them are West Nile, California group, Bhanja, Erve, Kemerovo group, Eyach, and Thogoto viruses. The ecologies and epidemiologies of these viruses are presented and their medical importance as travel-related diseases is discussed.

Experimental reproduction of proventriculitis using homogenates of proventricular tissue

Proventriculitis is a problem affecting the processing of broiler carcasses, particularly those processed at 4 to 5 wk of age. The proventriculus and the gastric isthmus connecting the proventriculus to the gizzard are enlarged and swollen and often rupture during processing, causing carcass contamination. This study suggested that a filterable agent found in homogenated proventriculi can cause lesions similar to those seen in field cases. Proventriculitis was produced independently of an effect on growth, and only unfiltered homogenate caused stunting. Field birds with severe proventriculitis were shown to have increased body weights compared with birds without proventriculitis or with milder lesions. Intestinal weakness was not associated with proventriculitis and field birds with the most severe proventriculitis had stronger intestines. Although infectious proventriculitis has generally been reported as one of the lesions associated with stunting syndrome, these data suggest that it may have an independent etiology.

Turkey rhinotracheitis virus isolated from broiler chicken with swollen head syndrome in Japan

Turkey rhinotracheitis (TRT) virus was first isolated from a commercial broiler chicken with swollen head syndrome (SHS) in Japan. At the same time, Newcastle disease virus (NDV), infectious bronchitis virus (IBV), avian reovirus (ARV), Escherichia coli (E.coli), Morganella morganii, and Proteus mirabilis were also isolated from the same broiler chicken. The presence of antibodies to TRT virus was confirmed in the sera of 34-day-old chickens of the flock with SHS, however the antibodies to TRT virus were undetectable in the sera of 17-day-old chickens. In this investigation, we confirmed avian pneumovirus infection in chickens in Japan, and the virus and other agents may be considered as a cause of SHS.

Epizootic hemorrhagic disease virus and bluetongue virus serotype distribution in white-tailed deer in Georgia

Serum samples collected from 1,396 white-tailed deer (Odocoileus virginianus) in five areas of Georgia (USA) from 1989 to 1991 were tested for precipitating and serum neutralizing (SN) antibodies to the enzootic North American epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) serotypes. Precipitating antibodies to the EHDV or BTV serogroups, as detected by agar gel immunodiffusion (AGID) tests, were present in 35%, 29%, and 39% of deer sampled in 1989, 1990, and 1991, respectively. Significant differences (P < 0.05) in precipitating antibody prevalence were detected between physiographic regions during all years. Antibody prevalence consistently was highest in deer sampled from the Coastal Plain (77%), followed by the Piedmont (33%), Ridge and Valley (29%), Barrier Island (5%), and Blue Ridge (2%) regions. All AGID-positive samples were tested by SN tests for antibodies against all North American EHDV and BTV serotypes (EHDV serotypes 1 and 2, BTV serotypes 2, 10, 11, 13, and 17). Criteria for previous exposure to a specific serotype were either detection of monospecific results or clusters of positive results against that serotype. Serologic evidence of previous exposure to EHDV serotypes 1 and 2, and BTV serotypes 11 and 13 was detected during all years. Predominant serotypes varied among years. In general, evidence of exposure to EHDV serotype 2 appeared annually while exposure to BTV serotype 13 and EHDV serotype 1 decreased and increased, respectively. To determine serotype diversity prior to 1989, 134 AGID-positive white-tailed deer serum samples collected from 1967 to 1988 also were tested by SN. Evidence of exposure to EHDV serotypes 1 and 2 and BTV serotypes 11, 13, and 17 was detected.

An epizootic of hemorrhagic disease in white-tailed deer (Odocoileus virginianus) in Missouri: necropsy findings and population impact

An epizootic occurred among white-tailed deer (Odocoileus virginianus) from July through October 1988 in Missouri (USA). From late July through September, nine necropsied deer had lesions of the peracute or acute forms of hemorrhagic disease (HD) or no apparent lesions, whereas two deer necropsied in October had lesions of the chronic form of HD. Epizootic hemorrhagic disease virus was isolated from two necropsied deer. Based on changes in population indices, there is evidence that deer populations declined in seven of Missouri's 57 deer management units from 1987 to 1990. Based on a deterministic model designed to simulate deer populations in management units, it appeared that summer and fall 1988 mortality ranging from 6% to 16% accounted for the population decreases in deer management units with population declines. Heavily hunted areas where high deer mortality was not reported in the summer and fall of 1988 did not have population declines. Based on these results, we believe that HD mortality was high and resulted in deer population declines in parts of Missouri when combined with hunting harvest.

Reovirus associated with excessive mortality in young bobwhite quail

Multiple submissions of bobwhite quail (Colinus virginianus) were received for diagnosis from a commercial-size quail operation. The history and clinical signs included respiratory distress, lethargy, and substantial mortality. Reovirus was recovered from quail in the first submission, and both reovirus and adenovirus were isolated from later submissions. To determine the pathogenicity of the isolated reovirus, the initial isolate was inoculated into young quail from a different source. Those inoculated by the subcutaneous route became lethargic, and more than half died during the 2 weeks of the trial. Reovirus was recovered from a high percentage of those inoculated by this route. To the authors' knowledge, the isolation of reovirus from quail has rarely been reported, and reovirus has never before been suggested as a pathogen in this species.

Serologic evidence for rabbit syncytium virus in eastern cottontail rabbits (Sylvilagus floridanus) in Ohio

Thirteen of 20 eastern cottontail rabbit (Sylvilagus floridanus) sera collected near Delaware, Ohio (USA) in 1991 were positive by indirect immunofluorescent antibody test (IFAT) for antibody to rabbit syncytium virus (RSV), a Kemerovo serogroup orbivirus. In addition, two of 10 domestic bovine sera and three of 30 sheep sera collected in southeastern Ohio gave weak positive IFAT reactions to RSV.

Sequence comparisons of a highly virulent infectious bursal disease virus prevalent in Japan

Variable cDNA regions in the VP2 gene of five highly virulent infectious bursal disease viruses (IBDVs) isolated in Japan were amplified by polymerase chain reaction (PCR) and sequenced. The nucleotide sequences of five highly virulent IBDVs were identical. Comparisons of the nucleotide and the deduced amino acid sequences with those of other strains of IBDV indicated that Japanese highly virulent IBDV is different from all other strains of IBDV that were compared. The number of amino acids that differed between strains (substitution score) showed that highly virulent IBDV is more closely related to European virulent strain 52/70 than to Japanese conventional strains. These results strongly suggest that a single strain of highly virulent IBDV that might have originated from a European strain is prevalent in Japan.

Ecological studies on reovirus pollution of rivers in Toyama Prefecture. II. Molecular epidemiological study of reoviruses isolated from river water

In order to clarify the source of reovirus pollution in river water, comparative surveys have been carried out between reovirus isolates from river water and those from sewage, human or animal, by making use of the analysis of genomic RNA-migration pattern of reovirus in polyacrylamide gel electrophoresis (electropherotype). The strains of reovirus serotype 1 and 2 isolated from river water were classified into 3 and 9 electropherotypes, respectively, and 8 out of these 12 types were also found among strains isolated from sewage or human. When the monthly distribution of the river isolates classified by electropherotypes was compared with that of the sewage isolates, there were cases in which strains of the same electropherotype were simultaneously isolated from both sources. The electropherotypes of 3 isolates from pig and field rodents were different from those of the other isolates. The electropherotype of an oyster isolate coincided with that of some of the isolates from humans and river water. These results indicate that the major source of reoviruses polluting river water may be the human excretion.

[Serological study of the incidence of murine viruses in a population of small wild rodents (Microtus pennsylvanicus Ord, 1815)]

The results of a serological survey of a free-living population of meadow voles (Microtus pennsylvanicus) in Pinawa, Manitoba (Canada) showed that these animals possessed antibodies to six of the eleven viruses tested for, namely: reovirus type 3, murine encephalomyelitis agent, ectromelia virus, murine adenovirus, murine hepatitis virus and lymphocytic choriomeningitis virus. The significant increase in the number of individuals possessing specific antibodies suggests that these viruses, or related viruses, may be responsible for the decline in the population studied.

Isolation of a virus serologically related to the bluetongue group from an outbreak of haemorrhagic disease among exotic deer in Saudi Arabia

In February 1991 a severe haemorrhagic disease affected exotic deer aged over six months in the Al-Hofuf area of the eastern region of Saudi Arabia. The morbidity rate was 40 per cent and the case fatality rate was 60 per cent. The clinical signs were high temperature (up to 41.5 degrees C), nasal discharge, slight salivation and lacrimation, congestion of the conjunctivae, torticollis, tremors when trying to stand, recumbency and coma leading to death. Post mortem examination revealed a severe haemorrhagic disease. A virus, serologically related to the bluetongue serogroup, was isolated from the deer. Sheep and goats kept on the same farm did not show any clinical signs. The epidemiology of the outbreak is discussed.

Pathogenicity and preliminary antigenic characterization of six infectious bursal disease virus strains isolated in France from acute outbreaks

Six isolates originating from acute outbreaks of infectious bursal disease recently reported in broiler and pullet flocks in France were studied with respect to their pathogenicity and their antigenic relatedness to the Faragher 52/70 reference strain. Although the mortality experimentally induced in susceptible chickens by the field strains was sometimes four times higher than that which followed the inoculation of the reference strain (16 to 48% versus 12%), neither mortality nor morbidity were observed in chickens previously vaccinated with a commercial live vaccine and then challenged under the same conditions. Agar gel precipitation tests demonstrated the existence of common antigens in the different strains, and high cross-neutralization indices measured in embryonated specific pathogen free eggs showed them all to belong to serotype I. These data are discussed with reference to previous European and North-American studies on the antigenic status of infectious bursal disease virus.

Prevalence of subclinical infectious bursal disease and its significance in India

From a total of 32 poultry flocks, 1,176 serum samples were screened by the agar gel precipitation test and 314 (26.7%) were positive for antibodies to infectious bursal disease virus (IBDV). Prevalence of infection on the farms ranged from 8.88 to 53.84 per cent. The prevalence was highest (61.82%) in chickens between 7 and 11 weeks old and lowest (3.92%) in those above 22 weeks of age. In commercial broilers and layers 51.61 and 17.78% respectively were seropositive reactors. The high prevalence of subclinical IBD and its economic significance are discussed.