Joseph L. Corn

Transmission dynamics of Toxoplasma gondii on a pig farm.

Transmission of Toxoplasma gondii infection on a pig farm in New England was investigated using genetic and ecological methods to (i) determine if infection of pigs was a result of a single source, such as in an epizootic situation (e.g. outbreak) or of multiple sources, such as in an enzootic situation, (ii) identify the main source species of infection to pigs and (iii) evaluate the role of the environment surrounding the farm as the source of infection on the farm. Genetic characterization of 25 T. gondii isolates from market pigs revealed three distinct genotypes with no evidence of recombinants. These data imply that at least three distinct exposure events occurred during the 7-month lifespan of these pigs. This genotype diversity is consistent with enzootic transmission of T. gondii on the farm. Cats were suspected as the main source of pig infection based on the high seroprevalence (>95%) in pigs. The presence of the two most common T. gondii genotypes in eight isolates from free ranging chickens on this farm corroborated the role of cats because chickens were probably infected through ingestion of oocysts in the soil. The seroprevalence of toxoplasmosis in 163 wild mammals and birds captured around the pig sties (overall 13.1%) increased with proximity to the pig sties. Thus, transmission of T. gondii was higher near the pig sties than in the surrounding environment probably because of increased density of oocysts there. We propose that the farm does not simply reflect its surroundings in terms of strain composition and risk of infection, but that it acts as a reservoir of strains from which the outflow of new infections into its surrounding environment is higher than the inflow.

Isolation of Mycobacterium avium subsp. paratuberculosis from free-ranging birds and mammals on livestock premises.

ABSTRACT Surveys for Mycobacterium avium subsp. paratuberculosis infection in free-ranging mammals and birds were conducted on nine dairy and beef cattle farms in Wisconsin and Georgia. Specimens were collected from 774 animals representing 25 mammalian and 22 avian species. Specimens of ileum, liver, intestinal lymph nodes, and feces were harvested from the larger mammals; a liver specimen and the gastrointestinal tract were harvested from birds and small mammals. Cultures were performed by using radiometric culture and acid-fast isolates were identified by 16S/IS900/IS1311 PCR and mycobactin dependency characteristics. M. avium subsp. paratuberculosis was cultured from tissues and feces from 39 samples from 30 animals representing nine mammalian and three avian species. The prevalence of infected wild animals by premises ranged from 2.7 to 8.3% in Wisconsin and from 0 to 6.0% in Georgia. Shedding was documented in seven (0.9%) animals: three raccoons, two armadillos, one opossum, and one feral cat. The use of two highly polymorphic short sequence repeat loci for analysis of 29 of the 39 strains identified 10 alleles. One allelic pattern broadly shared in domestic ruminants (“7,5”) appeared in approximately one-third of the wildlife M. avium subsp. paratuberculosis isolates studied. Given the few cases of shedding by free-ranging animals compared to the volume of contaminated manure produced by infected domestic ruminant livestock, contamination of the farm environment by infected wildlife was negligible. Wildlife may, however, have epidemiological significance for farms where M. avium subsp. paratuberculosis recently has been eliminated or on farms free of M. avium subsp. paratuberculosis but located in the geographic vicinity of farms with infected livestock.

Restricted Enzooticity of Hepatitis E Virus Genotypes 1 to 4 in the United States

ABSTRACT Hepatitis E is recognized as a zoonosis, and swine are known reservoirs, but how broadly enzootic its causative agent, hepatitis E virus (HEV), is remains controversial. To determine the prevalence of HEV infection in animals, a serological assay with capability to detect anti-HEV-antibody across a wide variety of animal species was devised. Recombinant antigens comprising truncated capsid proteins generated from HEV-subgenomic constructs that represent all four viral genotypes were used to capture anti-HEV in the test sample and as an analyte reporter. To facilitate development and validation of the assay, serum samples were assembled from blood donors (n = 372), acute hepatitis E patients (n = 94), five laboratory animals (rhesus monkey, pig, New Zealand rabbit, Wistar rat, and BALB/c mouse) immunized with HEV antigens, and four pigs experimentally infected with HEV. The assay was then applied to 4,936 sera collected from 35 genera of animals that were wild, feral, domesticated, or otherwise held captive in the United States. Test positivity was determined in 457 samples (9.3%). These originated from: bison (3/65, 4.6%), cattle (174/1,156, 15%), dogs (2/212, 0.9%), Norway rats (2/318, 0.6%), farmed swine (267/648, 41.2%), and feral swine (9/306, 2.9%). Only the porcine samples yielded the highest reactivities. HEV RNA was amplified from one farmed pig and two feral pigs and characterized by nucleotide sequencing to belong to genotype 3. HEV infected farmed swine primarily, and the role of other animals as reservoirs of its zoonotic spread appears to be limited.

PATHOGEN EXPOSURE IN FERAL SWINE POPULATIONS GEOGRAPHICALLY ASSOCIATED WITH HIGH DENSITIES OF TRANSITIONAL SWINE PREMISES AND COMMERCIAL SWINE PRODUCTION

Surveys for evidence of exposure to pseudorabies virus (PRV), Brucella suis, swine influenza virus (SIV; human-like H1N1, reassortant type H1N1, H1N2-like H1N1 and H3N2), porcine circovirus 2 (PCV 2), and porcine respiratory and reproductive syndrome virus (PRRSV) in feral swine (Sus scrofa) were conducted in areas where feral swine were geographically associated with high densities of transitional swine premises in South Carolina and high densities of commercial swine production in North Carolina. In South Carolina, 10/50 (20.0%), 7/50 (14.0%), and 29/49 (59.2%) feral swine tested antibody positive for PRV, B. suis, and PCV-2, respectively. Antibodies to PRRSV (0/49) and SIV (0/49) were not detected. In North Carolina, antibodies to PRV and B. suis were not detected in serum samples from 120 feral swine; however, antibodies to PRRSV (1/120 [0.8%]), PCV-2 (86/120 [71.7%]; these included 80 positives plus six suspects), and SIV (108/119 [90.7%]) were present. The presence of PRV and B. suis in South Carolina may have been due to the introduction of infected feral swine into the area or to a previous association of feral swine with infected transitional swine. Their absence in the North Carolina populations may have been due to the absence of these disease agents in the feral swine originally introduced into the area and the lack of a potential for contact with infected commercial swine. Feral swine associated with commercial swine in North Carolina may have been exposed to SIV subtypes circulating in commercial swine via airborne spread of SIV from commercial swine facilities. Feral swine seropositive for PCV-2 were prevalent in both states, which may indicate efficient transmission from commercial swine and transitional swine, or that PCV-2 is widespread in feral swine. The low prevalence of animals with antibodies against PRRSV may indicate a less-than-efficient means of transmission from commercial to feral swine. Additional epidemiologic studies are needed to understand the risks and mechanisms of transmission of disease agents among commercial, transitional, and feral swine, and the role of feral swine as reservoirs of these disease agents.

Persistence of Pseudorabies Virus in Feral Swine Populations

Serologic surveys for evidence of exposure to pseudorabies virus (PRV) in feral swine were conducted from November 2001 to April 2002 at 10 sites in the southeastern United States, where evidence of previous PRV exposure had been documented during 1979–89. Sera were tested in the field on the day of collection by latex agglutination. Maximum sample size per site was to be 30 animals, but sampling was discontinued before reaching this number when positive results were obtained. Positive results were obtained at all of the study sites, demonstrating long-term persistence of PRV in feral swine populations. Overall, 38 of 100 (38%) animals were positive for antibodies. Consistent results from latex agglutination tests conducted in the field and laboratory demonstrated that this test was useful as a rapid and reliable diagnostic tool when used in the field.

HEALTH PROTOCOL FOR TRANSLOCATION OF FREE-RANGING ELK

When considering an elk (Cervus elaphus) restoration program, wildlife managers must evaluate the positive and negative elements of translocation. We prepared this protocol to give an overview of health considerations associated with translocation of elk, with an emphasis on movement of free-ranging elk from western North America to the southeastern USA. We evaluated infectious agents and ectoparasites reported in elk from two perspectives. First, we made a qualitative estimate of the ability of the agent to be introduced and to become established. This was done using a selected set of epidemiologic factors. Second, if there was a good possibility that the organism could become established in the release area, the potential pathological consequences for elk and other wildlife, domestic animals, and humans were assessed via examination of the literature and consultation with other animal health specialists. The results of these evaluations were used to classify infectious agents and ectoparasites as low risk (n = 174), unknown risk (n = 10), and high risk (n = 9). We classified Anaplasma marginale, Anaplasma ovis, Mycobacterium paratuberculosis, Pasteurella multocida serotype 3, Elaphostrongylus cervi, Dicrocoelium dendriticum, Fascioloides magna, Echinococcus granulosus, Dermacentor albipictus, and Otobius megnini as unknown risks. High risk infectious agents and ectoparasites were the agent of chronic wasting disease, Brucella abortus, Mycobacterium bovis, Dermacentor andersoni, Ixodes pacificus, and Psoroptes sp. Parelaphostrongylus tenuis, Elaeophora schneideri, and a Babesia sp. are parasites endemic in the southeastern USA that may present a “reverse risk” and adversely affect elk if released in some parts of the region. We developed a five-component protocol to reduce the risk of introduction of high risk infectious agents and ectoparasites that included: (1) evaluation of the health status of source populations, (2) quarantines, (3) physical examination and diagnostic testing, (4) restrictions on translocation of animals from certain geographic areas or populations, and (5) prophylactic treatment.

Field evaluation of baits and baiting strategies for delivering oral vaccine to mongooses in Antigua, West Indies

A field study was conducted on Antigua, West Indies, to determine the feasibility of delivering an oral rabies vaccine or population control agent to free-ranging mongooses (Herpestes javanicus). Two biomarkers (tetracycline hydrochloride [THCL] and DuPont Oil Blue A® dye) and two bait types (DuPont polymer fish meal and polyurethane foam) were used to bait three study sites. Four hundred polymer baits containing both biomarkers were distributed at 36 central point bait stations (11 baits/station) on an 80 ha study site (5 baits/ha); 69% of the mongoose population consumed one or more baits. Two thousand baits containing THCL and 400 baits containing DuPont dye were distributed on two additional 100 ha study sites (24 baits/ha). Polymer fish meal baits were used on the first site and polyurethane baits on the second site. Based on the presence of biomarkers in bone or soft tissue, 96 to 97% of the mongooses at both sites consumed at least one bait. We conclude that oral baiting of mongooses is a feasible method for delivery of vaccines for the control of rabies in this species.

A SURVEY OF WILD SWINE IN THE UNITED STATES FOR EVIDENCE OF HOG CHOLERA

The results of surveillance for hog cholera (HC) in wild swine (Sus scrofa) collected from throughout the United States from 1979 to 1987 are presented. Sera collected from 1,218 wild swine and tissues from 637 were evaluated for HC antibodies and virus, respectively. Included within this surveillance were samples from Santa Cruz and Santa Rosa Islands, California, where HC virus had been deliberately introduced into wild swine during the 1950s in attempts to eradicate these animals. All evaluations were considered negative for HC. It appears that the HC virus does not maintain itself in dispersed swine populations and that wild swine have not remained a reservoir of HC since its eradication in domestic swine in the United States.

Tick Paralysis of a Snake Caused by Amblyomma rotundatum (Acari: Ixodidae)

Abstract A lethargic southern black racer, Coluber constrictor priapus Dunn and Wood, wild-caught in the Florida Keys, Monroe County, FL, was found to be paralyzed by the bite of a female ixodid tick, Amblyomma rotundatum Koch (Acari: Ixodidae). Removal of the tick restored the snake to normalcy within 18 h. Other, earlier reported cases of tick toxicosis in reptiles are reviewed and clarified. Evidently, the present incident is the only reported case of tick paralysis in a poikilotherm found in a natural setting.

Estimation of Density of Mongooses with Capture-Recapture and Distance Sampling

We captured mongooses ( Herpestes javanicus ) in live traps arranged in trapping webs in Antigua, West Indies, and used capture-recapture and distance sampling to estimate density. Distance estimation and program DISTANCE were used to provide estimates of density from the trapping-web data. Mean density based on trapping webs was 9.5 mongooses/ha (range, 5.9–10.2/ha); estimates had coefficients of variation ranging from 29.82–31.58% ( X = 30.46%). Mark-recapture models were used to estimate abundance, which was converted to density using estimates of effective trap area. Tests of model assumptions provided by CAPTURE indicated pronounced heterogeneity in capture probabilities and some indication of behavioral response and variation over time. Mean estimated density was 1.80 mongooses/ha (range, 1.37–2.15/ha) with estimated coefficients of variation of 4.68-11.92% ( X#x0304; = 7.46%). Estimates of density based on mark-recapture data depended heavily on assumptions about animal home ranges; variances of densities also may be underestimated, leading to unrealistically narrow confidence intervals. Estimates based on trap webs require fewer assumptions, and estimated variances may be a more realistic representation of sampling variation. Because trap webs are established easily and provide adequate data for estimation in a few sample occasions, the method should be efficient and reliable for estimating densities of mongooses.