Experimental contact of bighorn sheep (Ovis canadensis) with horses and cattle, and comparison of neutrophil sensitivity to Pasteurella haemolytica cytotoxins.

Peripheral blood neutrophils from horses, cattle, and Rocky Mountain bighorn sheep (Ovis canadensis canadensis) were evaluated for susceptibility to cytotoxin-dependent lysis of different biotypes and serotypes of Pasteurella haemolytica of domestic sheep, cattle, bighorn sheep, or mountain goat (Oreamnos americana) origin utilizing a cytotoxicity assay which measures the degree of bacteria cytotoxin-killing of neutrophils. All isolates of P. haemolytica (biotypes A and T) were noncytotoxic to horse neutrophils. Thirteen of 18 R haemolytica biotype A isolates were cytotoxic (> 50% neutrophil death in vitro) to bighorn sheep neutrophils, and four of 10 P. haemolytica biotype A isolates were cytotoxic to neutrophils of cattle; P. haemolytica biotype T (= Pasteurella trehelosi) isolates were noncytotoxic to neutrophils of bighorn sheep and cattle. When six bighorn sheep were pastured with three horses, only P. haemolytica biotype T isolates were recovered from the bighorn sheep throughout the study; Pasteurella spp. organisms were not isolated from the three horses. At initiation of a study where five bighorn sheep were pastured with three cattle, P. haemolytica biotype A, serotype 1, 2 was isolated from all three cattle, and only P. haemolytica biotype T isolates were recovered from the bighorn sheep. One bighorn sheep died in each of the horse and cattle copasturing experiments. Pasteurella haemolytica was not isolated from the bighorn sheep which died in the horse copasturing experiment. A noncytotoxic P. haemolytica biotype A, serotype 2 was isolated at necropsy from the bighorn which died in the cattle contact experiment. Based on these experiments, we believe bighorn sheep and horse association would not be detrimental to bighorns due to P. haemolytica induced pneumonia.

Susceptibility of Dall sheep (Ovis dalli dalli) to pneumonia caused by Pasteurella haemolytica.

We evaluated susceptibility of Dall sheep (Ovis dalli dalli) to bacterial pneumonia induced by two strains of Pasteurella haemolytica of domestic sheep origin by evaluating the sensitivity of blood neutrophils of eight Dall sheep to lysis by cytotoxins of P. haemolytica, and by intratracheal inoculation of three Dall sheep, two bighorn sheep (Ovis canadensis), and two domestic sheep with 3.7 x 10(6) or 2.5 x 10(7) colony forming units of P. haemolytica. Neutrophils from the Dall sheep were more sensitive to lysis by cytotoxins from supernatants of a P. haemolytica, biotype A, serotype 2 (A2), of domestic sheep origin, than were neutrophils from six bighorn sheep. This cytotoxic bacterium was the same isolate that was used for intratracheal inoculation of two Dall sheep and two domestic sheep. Inoculation of this cytotoxic P. haemolytica A2 resulted in fatal fibrinopurulent pleuropneumonia in the first Dall sheep within 24 hr of inoculation, and pneumonic lesions in the second Dall sheep before it was euthanized 52 hr after inoculation. This strain of P. haemolytica A2 did not cause respiratory disease when inoculated into two domestic sheep. A noncytotoxic strain of P. haemolytica; biotype T, serotype 3,4,10 of domestic sheep origin did not result in pneumonia in the third Dall sheep or two bighorn sheep. Prior to inoculation, P. haemolytica, biotype T isolates were obtained from all three Dall sheep, but none of these isolates was cytotoxic. At necropsy, cytotoxic P. haemolytica A2 was isolated from lungs and other tissues of the two pneumonic Dall sheep. Based on these results, we conclude that Dall sheep appear to be at least as sensitive as bighorn sheep to pneumonia caused by P. haemolytica A2 of domestic sheep origin. Because in vitro and in vivo results appear closely correlated in this and other studies, we believe with additional evaluation and standardization, neutrophil cytotoxicity tests may serve as a substitute for live animal challenges in future studies of pathogenic P. haemolytica in wild sheep.

Experimental infections of Sarcocystis spp. in Rocky Mountain elk (Cervus elaphus) calves.

Four 4-mo-old elk calves (Cervus elaphus) obtained from northeastern Oregon (USA) each were inoculated orally with 250,000 sporocysts of Sarcocystis spp., including S. sybillensis and S. wapiti. Three similar elk calves of comparable ages and weights served as uninoculated controls maintained with the inoculated elk during the experimental period between September and December 1993. Body weights were evaluated at 0 and 90 days postinoculation (PI); packed cell volumes of whole blood were evaluated at 0, 30, and 60 days PI, and numbers of sarcocysts in histologic sections from 11 selected tissues were evaluated at 90 days PI. Significant differences in blood packed cell volumes were not detected between groups (P > 0.05). Except for weight gain, elk remained healthy. Mean (+/- SE) weight gain of inoculated elk (27.1 +/- 1.6 kg) was significantly (P < 0.05) less than that of controls (40.2 +/- 4.9 kg). Mean (+/- SE) number of sarcocysts in tissues of inoculated (114.4 +/- 25.7 cm2) and controls (4.5 +/- 1.4 cm2) differed significantly (P < 0.05). Heart, esophagus and skeletal muscle contained the most sarcocysts. No sarcocysts were detected in brain, spinal cord, or testicles. Histologically, mononuclear myositis and myocarditis, with numerous intralesional sarcocysts were seen. Less severe, but widespread inflammation occurred in brain, spinal cord, and optic nerve. Mortality and anemia were not seen, but weight gain depression was detected in the inoculated elk over the 90 day experimental period.

Experimental infections of Eimeria wapiti and E. zuernii-like oocysts in Rocky Mountain elk (Cervus elaphus) calves.

Four Rocky Mountain elk (Cervus elaphus) 10 to 14 wk of age each were inoculated orally with a mixture of 50,000 sporulated oocysts of an Eimeria zuernii-like apicomplexan (70%) and E. wapiti (30%). Maximum numbers of oocysts per gram of feces (OPG) in each elk ranged from 985 to 15,517, but all calves remained healthy and clinical signs of coccidiosis were not observed. The prepatent period for E. zuernii was 8 days and the patent period approximately 37 days, with a maximum mean (+/- SE) recovery of 6,643 (+/- 3,756) OPG on post-inoculation day 8. The prepatent period for E. wapiti was 10 to 12 days and the patent period approximately 8 days, with a maximum mean recovery of 4,408 (+/- 2,308) OPG on postinoculation day 12. Based on these data, infections of E. zuernii and E. wapiti at the numbers given were not pathogenic in healthy elk calves.

A reliable transport method for isolating Pasteurella haemolytica from bighorn sheep.

We compared three transport methods for the recovery of Pasteurella haemolytica from pharyngeal swabs collected under field conditions from 42 bighorn sheep (Ovis canadensis) in one captive and three free-ranging populations. Transport methods included: Amies medium with charcoal, transported on ice, and cultured on blood agar within 24 hr; direct plating on blood agar, transported on heating pads, and incubated at 37 C within 8 hr of collection; and phosphate buffered glycerol (PBG), transported on dry ice, and stored at -70 C for 10 days before culture. Isolates of P. haemolytica were recovered from all 42 bighorn sheep with a mean (+/- SE) of 1.2 +/- 0.1 (Amies), 1.3 +/- 0.1 (blood agar), and 1.3 +/- 0.1 (PBG) isolates per swab. No statistical differences (P > 0.05) were observed in the recovery of P. haemolytica isolates among the transport methods. However, based on our experience and results of this study, we recommend that if submission of samples to the laboratory is likely to be delayed, pharyngeal swabs be transported in PBG on dry ice and kept frozen until they are cultured. Viable samples can be maintained in PBG at -70 C for several years.

Lead poisoning and other causes of mortality in trumpeter (Cygnus buccinator) and tundra (C. columbianus) swans in western Washington.

Lead poisoning and other causes of mortality of 115 trumpeter (Cygnus buccinator) and 21 tundra (C. columbianus) swans from northwestern Washington (USA) from 1986 to 1992 are reported. Necropsies were performed on all 136 swans, liver lead analysis conducted on 110, and differentiation between lead and steel shot pellets recovered from gizzards in 97 swans. Shot pellets were detected in 44 (32%) of 136 gizzards. Lead shot was recovered from 32 (33%) of 97 gizzards and steel shot from 16 (16%). Mean intensity of lead shot in gizzards was nearly five times greater than steel shot. Thirty-nine (35%) of 110 livers had lead concentrations diagnostic of lead poisoning (> 6 ppm, wet weight). Mean (+/- SE) weight for 61 non-lead poisoned trumpeter swans was 9.8 (+/- 0.30) kg, significantly heavier (P < 0.05) than 30 lead poisoned trumpeters (mean = 6.8 +/- 0.23 kg). There was no significant difference (P > 0.05) in weights between lead poisoned (n = 9) and non-lead poisoned (n = 12) tundra swans. Lead poisoning was the primary cause of death, accounting for 29% of the mortalities. Other causes of mortality identified were aspergillosis (17%), illegally shot (11%), and other traumatic factors (12%). The cause of death for 43 swans was not determined. Lead poisoning from the ingestion of lead shot continues to be a principal cause of mortality in swans overwintering in northwestern Washington.

Serological survey for heartworm (Dirofilaria immitis) in dogs in Washington.

The serologic prevalence of Dirofilaria immitis infection in 601 dogs in Washington was investigated in 1989-1990. Blood samples for serum were obtained from dogs approximately 2 yr of age or older in humane society shelters (n = 392) or veterinary clinics (n = 209). Serum samples were tested for heartworm infection using an enzyme-linked immunosorbent assay antigen test. Three (0.5%) dogs were positive for D. immitis infection, all of which were born and lived several years in states other than Washington. Heartworms have not been detected during the last 9 yr in the 1,203 dogs examined at the Washington Animal Disease Diagnostic Laboratory, Pullman, Washington. Consequently, the likelihood of indigenous heartworm infections in dogs in Washington remains low at this time.