The role of nematode parasites in Soay sheep (Ovis aries L.) mortality during a population crash.

In early 1989, two-thirds of the Soay sheep population on St Kilda died over 12 weeks. Post-mortem examinations revealed emaciated carcasses and considerable nematode burdens, with protein-energy malnutrition as the probable cause of death. Haematological and blood biochemical changes in the sheep, as well as fecundity of gastrointestinal nematodes, suggested the hosts were immunosuppressed. In parallel, laboratory experiments in which Soay sheep on a high plane of nutrition were artificially infected with Ostertagia circumcincta, showed no clinical signs or mortality when supporting worm burdens similar to those recorded in dead sheep on St Kilda. Anthelmintic treatment of a group of animals increased daily survival rates in ewes and male lambs, although treated animals became re-infected as the 'crash' progressed. It is suggested that parasites contribute to mortality in malnourished hosts, exacerbating the effects of food shortage.

Efficacy of Cydectin moxidectin 1% injectable against experimental infections of Dictyocaulus viviparus and Bunostomum phlebotomum superimposed on natural gastrointestinal infections in calves.

Twenty male Holstein calves averaging 105 kg in weight and naturally infected with gastrointestinal nematodes and small numbers of lungworm and hookworm, were given experimental infections with the two latter species to provide adult and larval stages for anthelmintic evaluation. Following random allotment, one group of 10 calves was injected subcutaneously with moxidectin at a dosage of 0.2 mg kg-1 of body weight. A second group of 10 was injected subcutaneously with unmedicated blank vehicle at a dosage of 1 ml per 50 kg of body weight. Fecal samples were examined before treatment and at 7 and 13 days after treatment. The 20 calves were necropsied for worm recovery at 13 and 14 days after treatment. All calves were positive for lungworm and hookworm on the treatment date. Treatment was 100% effective in elimination of hookworm eggs and lungworm larvae and 99.9% in reducing total egg counts at both 7 and 13 days after treatment. Moxidectin was 100% effective (P less than 0.01) in eliminating the following 11 species of nematodes. Dictyocaulus viviparus mature and immature adults (E5), Bunostomum phlebotomum adults and L4, Ostertagia ostertagi adults and early L4, Ostertagia lyrata adult males, Haemonchus placei adults. Trichostrongylus axei adults, Cooperia spp., including Cooperia punctata, Cooperia spatulata, and Cooperia pectinata adults, Oesophagostomum radiatum adults and Trichuris discolor adults. No adverse reactions to moxidectin treatment were observed.

Use of sentinel lambs for early monitoring of the South Powys Hydatidosis Control Scheme: prevalence of Echinococcus granulosus and some other helminths.

Sentinel lambs were used to identify young Echinococcus granulosus infections in sheep, to provide an early indication of the progress of the South Powys Hydatidosis Control Scheme. Four sentinel lambs were purchased on each of 60 farms, from inside and outside the control area; they were examined when approximately six, 10 and 15 months of age. Gross examination, thin slicing of organs and histological examination of the lesions in the viscera revealed no E granulosus hydatid cysts in lambs born within the control area, whereas 25 per cent of the 15-month-old lambs from outside the area harboured E granulosus cysts (less than 1 to 2 mm in diameter). Lambs from E granulosus infected farms had significantly higher anti-E granulosus ELISA antibody titres than lambs from uninfected farms. It was concluded that within one year of beginning to treat dogs with praziquantel every six weeks the transmission of E granulosus to sheep had ceased. In contrast, this treatment did not prevent infections with Taenia hydatigena or T ovis; an examination of the 240 lambs revealed T hydatigena in 33.3 per cent of them, Tovis in 4.2 per cent, Dictyocaulus filaria in 12.1 per cent and Meullerius capillaris in 49.2 per cent.

Distribution of Pasteurella haemolytica in the respiratory tracts of carrier calves and those subsequently infected experimentally with Dictyocaulus viviparus.

Distribution of Pasteurella haemolytica in the respiratory tracts of calves with no apparent clinical signs of illness and those infected experimentally with Dictyocaulus viviparus was determined so as to define carrier sites for this organism. The calves had been positive by nasopharyngeal swab for either P haemolytica A2 or A1 for at least two months or for over a month, respectively, before slaughter. P haemolytica A1 was acquired following horizontal spread from other infected calves. It was observed post mortem that P haemolytica A1 or A2 resided in the tonsils and retropharyngeal lymph nodes of calves of both groups. In addition to these sites, P haemolytica A1 was also isolated from the right cranial lung lobe of one of the calves from the D viviparus infected group although there was no evidence of pasteurella associated pneumonia. It was concluded that tonsil and retropharyngeal lymph nodes appear to be the most important carrier sites for P haemolytica when compared to other tissues of the bovine respiratory tract.

Experimental studies on anaemia in sheep infected with Dictyocaulus filaria.

The pathogenesis of Dictyocaulus filaria induced anaemia was experimentally investigated. Nineteen Dorset-Muzaffarnagri male lambs were divided into two groups of 13 and six. The lambs in the former group received a primary infection dose of 2000 D. filaria infective larvae, whereas animals in the latter group were kept as uninfected controls. The haematological alterations and faecal larval output were monitored weekly until day 220 post-infection. The infection caused an increase in erythrocyte sedimentation rate (ESR) and total leukocyte count (TLC). However, a decrease in packed cell volume (PCV), haemoglobin, total erythrocyte count (TEC) and blood pH was observed in acute infection. The shape and size of the erythrocytes, serum bilirubin level, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) remained unaffected In carriers, except for TEC, the values of these parameters returned to near-normal levels. The analysis of the results suggests that the infected animals developed a normocytic normochromic anaemia which persisted during the later stage of infection.

Isolation of Pilobolus spp. from the northern elk herd in Yellowstone National Park.

Pilobolus spp. were recovered from all fecal samples collected from an elk (Cervus elaphus nelsoni) herd in Yellowstone National Park (USA) with a high prevalence of Dictyocaulus viviparus infection. Pilobolus spp. have been shown to be important in the epizootiology of D. viviparus infections in cattle because these fungi aid in dissemination of larvae away from feces to areas where animals are more likely to ingest them, and protect larvae against dehydration and thus prolong survival. The same mechanism of dissemination of D. viviparus larvae may play a role in the epizootiology of these infections in elk.

Activity of luxabendazole against liver flukes, gastrointestinal roundworms, and lungworms in naturally infected sheep.

The anthelmintic potential of luxabendazole was investigated in sheep harboring mixed naturally acquired helminth infections. Results were assessed by comparing worm counts of the treated groups (seven animals each) on days 7-8 posttreatment with those of the nontreated control group, except for protostrongylid lungworms, for which the changes in pre- and posttreatment group mean larval counts/g feces were assessed for intensity effect. A single oral treatment at doses of 10.0 or 12.5 mg/kg body wt removed 97.6% of the adult Fasciola hepatica and 63.2%-83.8% of the Dicrocoelium dendriticum. Luxabendazole at 7.5, 10.0, and 12.5 mg/kg proved 100% effective in removing adult worms of the genera Haemonchus, Ostertagia, Trichostrongylus, Cooperia and Nematodirus as well as tissue-associated larval stages of gastrointestinal nematodes of the abomasal mucosa. The drug showed an intensity effect of 79.7%-87.6% against Strongyloides papillosus. Luxabendazole removed all Dictyocaulus filaria and reduced the fecal excretion of larvae of protostrongylid species (Protostrongylus rufescens, Neostrongylus linearis, Cystocaulus ocreatus, Muellerius capillaris) by 97.8%-99.6%. The efficacy of luxabendazole compared favorably with that of Diplin Kombi (oxyclozanide and levamisole), which was used as a reference drug.

[Is coccidiosis in mature cattle an exception?]. / Behoort coccidiose bij volwassen runderen tot een uitzondering?

An outbreak of coccidiosis in a group of forty Jersey cattle is reported. This group formed part of a population of 200 dairy cattle. Severe infection by Dictyocaulus viviparus occurred prior to this outbreak of coccidiosis. The two clinical pictures were confined to the group of Jerseys, which animals had been imported from Denmark during the previous autumn and winter (1983-1984).

An outbreak of eosinophilic bronchitis in horses possibly associated with Dictyocaulus arnfieldi infection.

Eight mature horses which had been affected with a moist cough for six weeks were found to have large numbers of eosinophils in tracheal mucus samples taken by transtracheal washing. These horses were kept on irrigated pasture and fed a hay-free diet. A companion yearling donkey was found to be passing Dictyocaulus arnfieldi larvae in its faeces. Two oral treatments with a dose of thiabendazole (440 mg/kg) resulted in the resolution of the clinical signs and the disappearance of eosinophils from transtracheal washings. The eosinophilic bronchitis seen in these horses was presumed to be a manifestation of prepatent D arnfieldi infestation.

Recurring hemolytic anemia, babesiasis, and influenza A viruses in a yak at low altitude in Nepal.

Episodes of hemolysis and leukocytosis which were associated with Babesia bigemina followed each of 3 challenge exposures to influenza A viruses. It is possible that viral infection altered the immunologic host-parasite equilibrium. Acute thrombocytopenia and rouleaux formation were also observed. Death, attributed to liver flukes, occurred 168 days after the yak was transferred from high to low altitude. A 2nd yak died of foot-and-mouth disease, thus supporting the Nepali belief that yaks will not survive at the lower altitudes of Kathmandu.