Overwintering strategies of a population of anthelmintic-resistant Haemonchus contortus within a sheep flock from the United States Northern Great Plains.

Haemonchus contortus infections have been increasingly reported in ungulates from cold climates even though past studies have shown that the free-living juveniles from this species survive poorly under freezing conditions. Overwintering strategies of H. contortus have not been documented in the Unites States Northern Great Plains. A PCR survey identified H. contortus as vastly predominant trichostrongyle species present (in addition to occasional detections of Teladorsagia sp.) in a closed farm flock of sheep from Brookings County, SD. Benzimidazole (BZ) and avermectin (AV) anthelmintics had been used intensely for many years on this flock. During the autumn season, three fecal egg count reduction tests (doramectin, albendazole, and moxidectin) were performed over a 4 year span to assess drug effectiveness within the flock. Significant drug resistance was found in Haemonchus adults with doramectin (69% efficacy), marginal resistance was found with albendazole (90% efficacy) and no resistance was found in moxidectin (100% efficacy). The following spring, pre-lambing and post-lambing fecals were obtained from albendazole and moxidectin treatment years to assess the resistance of the tissue-dwelling fourth-stage juveniles (J4s) at those times. Albendazole treated pre-lambing fecals averaged only 4 EPG and treated post-lambing fecals increased to 454 EPG, indicating that many of the J4s were not killed during the autumn treatment. Moxidectin pre-lambing fecals averaged only 1 EPG, and post-lambing fecals only increased to 6 EPG in the treated moxidectin population and 1422 EPG in the untreated moxidectin population. In addition to evaluating the ability of H. contortus to overwinter as drug resistant tissue-dwelling J4s, this study also evaluated the overwintering ability of pasture-dwelling, free-living third-stage juveniles at this farm. In the summers of 2010 and 2011, naïve tracer lambs were placed on a H. contortus contaminated pasture for 3 weeks to assess J3 winter survival. In 2010, tracer lambs only averaged 7 EPG whereas drylotted control lambs averaged 2 EPG; in 2011, tracer lambs averaged 2 EPG while the control lambs averaged 1 EPG. These results suggest that at this northern plains farm, yearly transmission of H. contortus is predominately through drug-resistant J4s. This is consistent with other cold-climate, overwintering studies involving H. contortus from Europe.

Detection and duration of porcine reproductive and respiratory syndrome virus in semen, serum, peripheral blood mononuclear cells, and tissues from Yorkshire, Hampshire, and Landrace boars.

Because transmission of porcine reproductive and respiratory syndrome virus (PRRSV) can occur through boar semen, it is important to identify persistently infected boars. However, even for boars given the same PRRSV strain and dose, variability in the duration of viral shedding in semen has been observed, suggesting that host factors are involved in PRRSV persistence. To determine whether there are host genetic factors, particularly litter and breed differences related to the persistence of PRRSV, 3 litters from 3 purebred swine breeds were used for this study. It was also determined whether PRRSV could be detected for a longer period of time in serum, semen, or peripheral blood mononuclear cells (PBMC) and if PRRSV could still be detected in tissues after these antemortem specimens were PRRSV negative for a minimum of 2-3 weeks. Three Hampshire, 3 Yorkshire, and 2 Landrace PRRSV-naive boars were obtained and inoculated intranasally with a wild-type PRRSV isolate (SD-23983). All boars within each breed were from the same litter, and litters were within 9 days of age. Serum and PBMC were collected twice weekly from each boar and analyzed for the presence of PRRSV by virus isolation and the polymerase chain reaction (PCR). Serum was also used to obtain virus neutralization titers and enzyme-linked immunosorbent assay S/P values. Semen was collected twice weekly from 7 of 8 boars and analyzed by PCR. After all specimens were PRRSV negative for a minimum of 2-3 weeks, each boar was euthanized, and 21 tissues plus saliva, serum, feces, and urine were collected. All postmortem specimens were evaluated by virus isolation. Specimens that were PRRSV negative by virus isolation were then evaluated by PCR. The mean number of days (+/-SD) for the duration of PRRSV shedding in semen was 51+/-26.9 days, 7.5+/-4.9 days, and 28.3+/-17.5 days for Landrace, Yorkshire, and Hampshire boars, respectively. Because of small sample sizes and large SDs, the differences in duration of PRRSV shedding in semen between breeds were not considered significant. However, the trend suggested that Yorkshire boars were more resistant to PRRSV shedding in semen than were Landrace boars, requiring further investigation using a larger numbers of boars. PRRSV was detected for a longer period in semen than in serum or PBMC in 4 of 7 boars. Viremia could be detected for a longer period in serum than in PBMC in 6 of 8 boars. After a minimum of 2-3 weeks of PRRSV-negative serum, semen, and PBMC, PRRSV could still be detected in the tonsil of 3 of 8 boars by virus isolation, indicating that boars still harbor PRRSV within the tonsil even though antemortem specimens are PRRSV negative.

Clinical and clinicopathologic characteristics of ovine GM-1 gangliosidosis.

Ovine GM-1 gangliosidosis is an inherited lysosomal storage disease. Nine lambs affected with the disease were studied to characterize clinical signs and to determine if there were any pathognomonic clinicopathologic abnormalities. Evaluation included physical, ophthalmic, and neurologic examinations, complete blood counts, serum enzyme and electrolyte analyses, urinalyses, cerebrospinal fluid analyses, blood gas analyses, roentgenograms, electromyograms, and electrocardiograms. Two affected lambs had clinicopathologic tests performed before and after the onset of clinical signs. The only consistent abnormalities recognized were nonspecific signs referable to the central nervous system; predominantly ataxia, conscious proprioceptive deficit most severe in the hind limbs, blindness, and recumbency. Lambs continued to eat and drink, though at diminished levels and with loss of body condition. It was concluded that there are no pathognomonic clinicopathologic abnormalities associated with ovine GM-1 gangliosidosis, and antemortem diagnosis requires enzyme assay of leukocytes or cultured fibroblasts, or lectin histochemistry of tissues obtained by biopsy. Lysosomal storage diseases should be considered among the differential diagnoses in young animals presenting with early neonatal death or with nonspecific neurological signs, in concert with an absence of diagnostic clinicopathologic findings.

Differential antibody responses to Corynebacterium pseudotuberculosis in sheep with naturally acquired caseous lymphadenitis.

Enzyme-linked immunosorbent assays (ELISA) with Corynebacterium pseudotuberculosis cell wall and bacteria-free supernatant with exotoxin preparations as antigens, and hemolysis inhibition tests were used to detect antibodies in the sera of adult range sheep with naturally acquired caseous lymphadenitis (CL). The extent and severity of lesions were quantitated on the basis of a lesion score, derived from an examination of the carcass (peripheral lymphoid tissue) and viscera (including internal lymphoid tissue) at the time of slaughter. The overall prevalence of C pseudotuberculosis-positive CL lesions in 104 sheep was 31.7%. The cell wall ELISA detected antibodies in 96.9% (32/33) of sheep with C pseudotuberculosis-positive CL lesions. The exotoxin ELISA detected antibodies in 84.8% (28/33) of positive sheep in the same group. Both ELISA resulted in a high number of apparent false-positives, with 64.7% and 49.2%, respectively, positive optical density (OD) values in sheep with no gross CL lesions and no apparent C pseudotuberculosis infection. There was no significant relationship between the extent of lesion development (lesion score) and OD values in both cell wall (r = 0.472) and exotoxin (r = 0.464) ELISA. Similarly, there was no significant relationship between the titer of antitoxin antibodies, as measured by the hemolysis inhibition test, and the extent of disease. These investigations indicate that those ELISA that use crude C pseudotuberculosis antigens are of questionable utility in the field, where C pseudotuberculosis infection is endemic in many sheep populations. Furthermore, these studies suggest that antibodies that are reactive with components of C pseudotuberculosis and that develop in response to infection may have little impact on the recovery of the host.

Avian cholera in a gyrfalcon (Falco rusticolus).

A 2-year-old female gyrfalcon (Falco rusticolus) was being used to hunt ducks in southeastern Wyoming during an outbreak of avian cholera in waterfowl and wild turkeys. While out overnight, the falcon consumed a bird. Within 24 hours the falcon was anorectic, and it was found dead approximately 48 hours following ingestion of wild prey. Gross and microscopic lesions were typical of avian cholera, and Pasteurella multocida serotype 1 was isolated from tissues of the falcon.