A brief history of the Society for Tropical Veterinary Medicine.
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Biomedical subjects
E P Gibbs
Publications and source records attributed to E P Gibbs.
Safety testing of needle free, jet injection devices to detect contamination with blood and other tissue fluids.
Needle free jet injection guns have been used extensively in both veterinary and human health to deliver both vaccine and drugs, but in recent years, concerns have mounted for their potential to transmit blood borne disease agents among consecutive vaccinates. A Ped-O-Jet type jet injection device was used to deliver serial subcutaneous injections of 0.5 mL saline (as a surrogate for vaccine) into calves and pigs, with intervening ejectates collected in vials to represent what the next vaccinate would have received. An enzyme linked immunosorbant assay was developed to detect species specific albumin as a marker for blood, using calibration standards from known dilutions of bovine or porcine blood. Assay sensitivity of 20 pL/mL corresponded to the estimated minimal chimpanzee infectious dose of 10 pL for hepatitis B virus. The methodology and available results for evaluating the safety of jet injector devices are reported.
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Genital infection and transmission of pseudorabies virus in feral swine in Florida, USA.
Seventeen feral swine (FS) naturally infected with pseudorabies virus (PRV) and treated with dexamethasone (4 mg/kg body wt) on five consecutive days shed virus primarily from the genital tract and less frequently from the upper respiratory tract. The FS isolates were identified as PRV by virus neutralization with specific polyclonal antiserum and by direct immunofluorescence. Restriction endonuclease analysis with BamHI showed that representative samples from a total of 62 isolates were identical to each other, but differed in at least 5 DNA bands from the PRV Shope reference strain profile. DNA purified from FS isolates propagated in Vero cells or DNA extracted directly from genital swabs were amplified in the polymerase chain reaction using primers specific for the gpII (gB) gene of PRV. This amplification yielded a product of the expected size (200 bp), which specifically hybridized to a digoxigenin-labelled 30-mer probe complementary to an area within the region defined by the primers. In a transmission experiment, PRV was recovered from the vagina at 1 and 6 weeks after uninfected feral gilts were mixed with infected feral boars. PRV was not isolated from the upper respiratory tract of either gilts or boars. At eight weeks, 4 of the 5 gilts had developed low titer neutralizing antibodies to PRV. Our results indicate that PRV in FS is transmitted through sexual contact.
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Mechanisms of transmission of Aujeszky's disease virus originating from feral swine in the USA.
To understand the possible mechanisms of transmission of Aujeszky's disease virus (pseudorabies or PRV) from a feral pig reservoir, intranasal infections were initiated in domestic pigs and in pigs from a herd derived from captured feral pigs. Virus strains originating from feral pigs and from domestic pigs were compared. Similar shedding patterns were obtained in both feral-derived and domestic pigs, however, virus strains from feral pigs were markedly attenuated. Virus could be isolated after acute infection from nasal secretions, tonsils and occasionally from genital organs. In studies of transmission of PRV by cannibalism, either latently infected or acutely infected tissue was fed to both domestic and feral-derived pigs. In two similar experiments, latently infected tissue did not transmit virus, but tissues from acutely infected pigs did transmit infection. Cannibalism was observed typically in both types of pigs older than 6 weeks of age. It was concluded that transmission of PRV originating from feral pigs can occur by several mechanisms including the respiratory route and by cannibalism of pigs that die of acute infection. Transmission of PRV from feral swine may, however, result in sub-clinical infection.
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The public health risks associated with wild and feral swine.
Wild swine populations (Sus scrofa) are present in many regions of the world. Large feral populations in North America and Australia are principally derived from introduced domestic pigs. In Europe, most wild boar are found in Germany and Poland. While wild swine are certainly a significant reservoir of infection for domestic swine diseases (for example, African swine fever virus in wild boar in Sardinia), these swine generally do not constitute a major public health risk. Brucella suis infections and trichinellosis are the most important zoonotic threats to public health.
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Evaluation of swinepox virus as a vaccine vector in pigs using an Aujeszky's disease (pseudorabies) virus gene insert coding for glycoproteins gp50 and gp63.
Pigs were vaccinated by scarification or intramuscular injection with a swinepox virus-Aujeszky's disease (pseudorabies) recombinant (rSPV-AD) constructed by inserting the linked Aujeszky's disease virus genes coding for glycoproteins gp50 and gp63, attached to a vaccinia virus p7.5 promoter, into the thymidine kinase gene of swinepox virus. By 21 days after vaccination, 90 and 100 per cent of the animals vaccinated by scarification or intramuscular injection, respectively, had developed serum neutralising antibodies to Aujeszky's disease virus. Upon challenge with virulent virus, significantly fewer vaccinated pigs developed clinical Aujeszky's disease, nasal shedding of challenge virus was markedly reduced, and the vaccinated groups of pigs maintained or gained weight during the week after challenge whereas the unvaccinated control group lost weight. No transmission of rSPV-AD to in-contact controls was detected during the three weeks before challenge. In a second experiment, serum neutralising antibodies to Aujeszky's disease virus persisted for 150 days after the pigs were vaccinated with rSPV-AD by scarification or intramuscular injection and all the pigs showed an anamnestic response when they were revaccinated.
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Vector competence parameters of Culicoides variipennis (Diptera: Ceratopogonidae) for bluetongue virus serotype 2.
Culicoides variipennis (Coquillett), the only proven vector of bluetongue virus (BLU) in the western hemisphere, was evaluated as a vector of bluetongue virus serotype 2 (BLU 2). This serotype was isolated from sentinel cattle in south Florida at a site devoid of C. variipennis. Culicoides variipennis readily fed on a mixture of defibrinated blood and BLU 2 through chicken skin membrane. An infection rate of 46.2% was obtained. A growth curve of virus titers recovered from orally infected flies showed a linear relationship between the virus titers and the period of extrinsic incubation. Culicoides variipennis also became infected when inoculated intrathoracically with BLU 2. Peak titers were higher and more rapidly attained in inoculated flies when compared with orally infected flies. Infected C. variipennis also transmitted BLU 2 to sheep via bite. These results demonstrate that C. variipennis is a potential biological vector of BLU 2 in the laboratory. The implication of this on the epidemiology of BLU 2 in the United States is that BLU 2 should have become more widespread in ruminants in the United States. The fact that this has not occurred during the past 10 yr is discussed.
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Epidemiology of bluetongue in Central America and the Caribbean: initial entomological findings. Regional Bluetongue Team.
Forty-four species of Culicoides (Diptera: Ceratopogonidae) were caught in insect light traps during the first 2 years of studies on the epidemiology of bluetongue virus in the Caribbean and Central America. Traps were operated near sentinel ruminants which were bled monthly for serologic evaluation and then virus isolation. More than 570,000 individuals were identified. Culicoides insignis Lutz accounted for 90% of the catch, C. filarifer Hoffman/C. ocumarensis Ortiz 5%, C. furens Poey 3% and C. pusillus Lutz 2%. Other species accounted for less than 1% of the total catch. Sentinel ruminants became seropositive when C. insignis populations were high at many study sites. At a few sites C. pusillus and C. filarifer/C. ocumarensis were predominant or were present in large numbers during seroconversions of sentinels. Virus isolations were obtained from sentinel ruminants during times when these same species were present in large populations.
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Prevalence of pseudorabies (Aujeszky's disease) virus antibodies in feral swine in Florida.
Serum samples collected from feral swine (Sus scrofa) throughout Florida (USA) from 1980 to 1989 were tested for antibodies to pseudorabies virus (PRV) by the serum neutralization test, the latex agglutination test, or by the enzyme-linked immunosorbent assay. Seropositive swine were detected at 11 of 13 sites with a composite seroprevalence of 34.8% (579 of 1,662 samples; range = 5.9% to 58.2%) for sites with seropositive swine. Data on age and sex of the swine were available from three sites. Seroprevalence in males and females did not differ significantly (P = 0.62 for the combined data). Seroprevalence in adult (> or = 8 mo) and juvenile swine (< 8 mo) was significantly different at all sites (P < 0.05 for the combined data). From these data, PRV infections appear to occur widely in populations of Florida feral swine and may seriously undermine efforts to eradicate this virus from the domestic swine population of the USA.
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Epidemiology of bluetongue viruses in the American tropics. Regional Bluetongue Team.
A study of the epidemiology of bluetongue viruses is in progress with the collaboration of 11 Central American and Caribbean countries. To date, over 200 bluetongue virus isolates have been obtained from cattle and sheep in sentinel groups distributed in the participating countries. Bluetongue serotypes identified include 1, 3, 6, and 12, virus types not previously recorded in the Western Hemisphere. Although the clinical impact of bluetongue virus infections in this hyperendemic environment appears to be minimal, the ubiquity of infection causes restrictions on the export of ruminant livestock and germ plasm. The stability of the Caribbean region ecosystem and the long-range implications of the interface with the northern temperate bluetongue virus ecosystem are reviewed.
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Evaluation of Culicoides insignis (Diptera: Ceratopogonidae) as a vector of bluetongue virus.
Based upon epidemiological evidence, Culicoides insignis Lutz is a probable biological vector of bluetongue viruses (BTV) in South Florida, the Caribbean Region and Central America. The vector potential of this species for BTV was evaluated in the laboratory in a series of experiments using insects caught in the field. Although there was great variation in the percentage of flies that fed from any one catch, it was demonstrated that C. insignis became infected after membrane feeding on a mixture of blood and virus. The infection rates ranged from 20 to 62.5%. Following intrathoracic inoculation, BTV replicated to high titres in C. insignis. Such flies were also shown to be capable of transmitting BTV to susceptible sheep and embryonated chicken eggs. This series of experiments provides the first conclusive evidence that C. insignis is a biological vector of bluetongue virus. This is the first proven vector of BTV in the neotropics.
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Isolation and molecular characterization of the swinepox virus thymidine kinase gene.
Swinepox virus (SPV), the only member of the Suipoxvirus genus, shows little antigenic relatedness or DNA homology to members of the other poxvirus genera. A SPV thymidine kinase (TK) gene was detected and mapped to the left end of the HindIII G fragment using degenerate oligonucleotide probes. Cloning and sequencing of a 1.8-kb HindIII-BamHI fragment containing the SPV TK gene revealed an open reading frame (ORF) of 181 amino acids yielding a predicted polypeptide of Mr 20.6 kDa with significant homology to both poxvirus and vertebrate thymidine kinases. Comparison with other TK protein sequences showed that the SPV thymidine kinase was closely related to the TK genes of avipoxviruses (52.0%) and vertebrates (57.1-59.7%). The TK gene from African swine fever virus (ASF) showed little homology (30.5%) to the SPV TK gene suggesting that these two viruses are not closely related though they share many biochemical features and infect a single, common mammalian host (swine). The SPV TK gene, like that of other poxviruses, is transcribed early, and when cloned into a TK- strain of vaccinia converted the virus to a TK+ phenotype. BUdRR mutants of SPV contained frameshift, deletion, and missense mutations in the TK ORF.
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Seroepidemiology of Bivens Arm virus infections of cattle in Florida, St. Croix and Puerto Rico.
Bivens Arm virus (BAV) is a newly discovered rhabdovirus infecting cattle and water buffalo in Florida. The virus is classified as a member of the Tibrogargan group, members of which have hitherto been found only in Australasia. They are considered to be transmitted by Culicoides species. Bivens Arm virus was first isolated from Culicoides insignis which suggests that BAV is also transmitted by this genus. A serological survey of two small groups of cattle raised in St. Croix and Puerto Rico, in the Caribbean, established that antibody to BAV, or a closely related virus, exists on both island. A retrospective analysis of seroconversions to BAV in sentinel calves in Florida, relative to populations of potential Culicoides vectors, failed to demonstrate any statistically significant correlation.
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A comparison of differential diagnostic tests to detect antibodies to pseudorabies glycoproteins gX, gI, and gIII in naturally infected feral pigs.
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Culicoides spp. (Diptera: Ceratopogonidae) associated with cattle in St. Croix, Virgin Islands, and their relevance to bluetongue virus.
Potential biting midge vectors were collected at two sites on St. Croix as part of an ongoing study on the epidemiology of bluetongue viruses in the Caribbean region. Six species of Culicoides were trapped in a New Jersey light trap (mean = 173 biting midges/trap night) near cattle on a dairy farm. C. furens (Poey) and C. insignis Lutz were the predominant phototactic species, and C. pusillus Lutz, C. trilineatus Fox, C. jamaicensis Edwards, and C. phlebotomus (Williston) were collected less frequently. Four species of Culicoides were aspirated from bovine bait during the morning and evening crepuscular periods with a modified car vacuum. C. furens was aspirated primarily from the ventral portions of the bovine host, whereas C. insignis and C. pusillus were collected principally from the dorsum, and C. trilineatus was collected equally from all aspects. At least one individual of each of these aspirated species was blood engorged. Because C. furens, C. insignis, C. pusillus, and C. trilineatus were most abundant and feed on cattle, they deserve further consideration as vectors of bluetongue virus on St. Croix.
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Bluetongue epidemiology in the Caribbean region: serological and entomological evidence from a pilot study in Barbados.
Variation in the percentage of lambs seroconverting to bluetongue viruses was seen between sites and years in Barbados. Transmission at some sites was nearly absent whereas all lambs at one site became seropositive. The agar gel immunodiffusion test for bluetongue gave consistent results in series of serum samples from 112 of 121 sentinel lambs. Collections of biting midges in association with sheep yielded six species: Culicoides insignis Lutz, C. pusillus Lutz, C. phlebotomus (Williston), C. furens (Poey), C. jamaicensis Edwards and C. trilineatus Fox. The first two species comprised 92% of those caught during a sentinel lamb study and were the predominant species trapped for virus isolation. No viruses were recovered from 5517 C. insignis, 614 C. pusillus, three C. trilineatus and two C. furens placed into pools during two brief intensive trapping operations.
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Serologic survey for transmissible gastroenteritis virus neutralizing antibodies in selected feral and domestic swine sera in the southern United States.
Serum samples collected from feral and domestic swine (Sus scrofa) in Florida and feral swine in Georgia and Texas were assayed by plaque reduction for their virus neutralizing (VN) antibodies against the porcine transmissible gastroenteritis virus (TGE). None of 560 samples collected from feral swine contained VN antibodies for TGE virus, but experimentally infected feral swine seroconverted. None of 665 samples from domestic swine contained TGE-VN antibodies. These results indicate feral swine are not a significant reservoir for TGE virus in southern states, but are capable of becoming infected and developing VN antibodies against TGE.
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Epidemiologic study of bluetongue viruses in Central America and the Caribbean: 1986-1988. Regional Bluetongue Team.
Results of a prospective serologic and virologic study of ruminant livestock in Central America and the Caribbean islands revealed bluetongue virus (BTV) to be enzootic in the 9 countries participating in the study. Bluetongue virus serotypes 1, 3, 6, and 12 were isolated from sentinel animals. To the authors' knowledge, these are the first isolations of BTV from the region studied and the first isolations of these serotypes in the Western Hemisphere. Clinical disease attributable to BTV infection was not observed in sentinel animals. The incidence pattern, with respect to age and geographic location, was determined. The need to evaluate the epizootiologic features or arthropod-borne viruses (arboviruses) on a regional ecologic basis is stressed.
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