Ovine systemic pasteurellosis caused by Pasteurella haemolytica biotype T.

A detailed study was made of lambs aged 5--7 months naturally infected with Pasteurella haemolytica biotype T. In addition to the well known features of such infections, previously unreported necrotic lesions of the tonsil, oesophagus, pharynx and adjacent areas were consistently seen. Large numbers of P. haemolytica were present in the tonsil, oesophageal lesions, lung, liver and spleen, but few or none in other tissues. The evidence indicated that the disease was not a true septicaemia. It is postulated that P. haemolytica biotype T already present in the tonsils multiplies and invades the adjacent tissues of the upper alimentary tract; groups of organisms from this site enter the blood stream as emboli, most of which lodge in the capillary beds of the lung and liver; rapid multiplication of organisms in these tissues leads to death from the effects of endotoxin.

Contagious bovine pleuropneumonia: mouse-protective antibody in the sera of infected and vaccinated cattle.

Cattle produced humoral mouse-protective antibody (MPA) to Mycoplasma mycoides var mycoides as a result of natural infection, hyperimmunisation, vaccination with well-known strains of living vaccines or vaccination with killed cultures. Bovine MPA was distinct from complement-fixing and precipitating antibodies and was frequently detected in their absence, particularly in the sera of vaccinated--as opposed to naturally infected--cattle. In view of its defensive role in artificially-infected mice, it seems likely that such antibody plays a part in resistance to the disease in cattle. High levels of MPA followed inoculation of cattle with killed concentrated culture containing adjuvant; this finding merits further investigation, as it may lead to improved methods of vaccination.

Virulence of established vaccine strains and artificially passaged field strain of Mycoplasma mycoides subsp mycoides.

The virulence of Mycoplasma mycoides for mice, which appears to parallel virulence for cattle, was assessed in respect of four vaccine strains well known for their use in the control of contagious bovine pleuropneumonia. The T1 strain was slightly more virulent than V5, and both were much more virulent than F and KH3J, which could not be distinguished from each other. There was no significant difference between cultures of the T1 strain supplied by three different vaccine-producing laboratories, The mousevirulence test was also used to study the effect of serial passage in artificial systems on virulent field strains of M mycoides; two such strains underwent no appreciable change in virulence during many passages in chick embryos or in mice, although the same strains, and two others, were readily attenuated by repeated subculture in broth. With one strain of M mycoides there was evidence that the total number of subcultures in broth over a given period was more important than the duration of each subculture.

The virulence of vaccine strains of Mycoplasma mycoides var. mycoides recovered from inoculated cattle.

The T1 and KH3J attenuated strains of M mycoides, well-known in Africa for immunisation against contagious bovine pleuropneumonia, were recovered from the lymph nodes of cattle at intervals up to three months after vaccination. Virulence titrations in mice indicated that the organisms recovered from cattle were of no greater virulence than the strains used for inoculation. There was, therefore, no suggestion that the use of attenuated vaccines in the field might be associated with reversion to virulence after inoculation.

Inhibition of the growth of some strains of Mycoplasma mycoides subsp mycoides by the blood of certain horses.

When incorporated in solid medium at a concentration of 15 per cent, the defibrinated blood of certain horses strongly suppressed the growth of some, but not all, strains of Mycoplasma mycoides subsp mycoides so that many colonies failed to develop to a visible size. Blood from a single rabbit was tested and found to exert a similar effect. There was striking variation in the degree of inhibition produced by different samples of horse blood and, of five strains of the organism examined, the T1 vaccine strain was the most susceptible. The results suggested that the effect was not due to antibody.

Faecal thiaminase in clinically normal sheep associated with outbreaks of polioencephalomalacia.

Three flocks in which in with one of more sheep had succumbed to polioencephalomalacia (cerebrocortical necrosis) were used for faecal thiaminase studies. Up to one third of the clinically normal animals in these flocks to be excreting thiaminase on any one day and over half the flock could be thiaminase excretors at some time during an outbreak. The possible detrimental effects of sub-clinical thiamine antagonism in sheep are therefore worthy of consideration. Thiaminase excretion by individual animals was variable and sometimes intermittent. It was unaffected by changes in diet, pasture or enviroment. In two of the flocks multiple cases of polioencephalomalacia followed the administration of the anthelmintics, levamisole hydrochloride and thiabendazole. This aspect merits further investigation in view of the widespread use of anthelmintics of this type, especially as the profuse diarrhoea which can be associated with outbreaks of polioencephalomalacia may be wrongly attributed to gastro-intestinal parasitism.

Haemorrhagic syndrome of cattle of suspected mycotoxic origin.

An outbreak of disease characterised by haemorrhages, anaemia, leucopenia, thrombocytopenia, skin lesions, degenerative and inflammatory tissue changes and death was investigated in herd of dairy cows. A tentative diagnosis based on circumstantial evidence was of mycotoxicosis arising from the feeding of mouldy barley.

Field studies on enzootic abortion of ewes in south east Scotland.

Statistical data were collected from 20 sheep flocks in which enzootic abortion of ewes (EAE) was diagnosed by examination of fetal material and maternal blood samples. The abortion rate in the 10,645 ewes in these flocks was 7.6 per cent. Thirteen of the flocks were fully vaccinated against EAE but the abortion rate in these was still in the order of 6.5 per cent. EAE was the major cause of the problem as ascertained from the laboratory examination of samples from a wide range of cases of abortion. There is therefore evidence that, in some flocks in south east Scotland, the efficacy of the vaccine against EAE is unsatisfactory. The reasons for this are discussed.

Acute nephropathy in young lambs.

Acute renal failure was diagnosed by clinical, necropsy and histological criteria in 39 flocks (20 low ground, 13 hill and six marginal upland) in areas served by six veterinary investigation centres. Forty-eight lambs of 12 different breeds or crosses were investigated. The mean age of affected lambs was 38 days (range seven to 84 days); 21 lambs (44 per cent) were aged seven to 28 days, while only eight (17 per cent) were older than two months. Mortality in clinically affected lambs was almost 100 per cent, with no response to various treatments. Histological examination showed that 40 lambs (83 per cent) had nephrosis, while the rest had toxic tubular necrosis, interstitial nephritis or tubular damage associated with oxalate crystal deposits. Only about half of the lambs had any evidence of enteric infections or enteropathy. Acutely ill lambs had azotaemia, haemoconcentration and proteinuria; some lambs had glycosuria or haematuria. Samples of plasma from 22 lambs with nephrosis were compared with similar samples from 82 incontact but asymptomatic lambs. The clinically affected group had significantly elevated plasma urea, creatinine, total protein, globulin, phosphorus and chloride concentrations and significantly reduced plasma calcium concentrations compared with healthy lambs. Affected lambs had a significant reduction also in the calcium:phosphorus ratio. No significant differences between groups was found in plasma concentrations of albumin, glucose, lactate, glycerol, creatine kinase, alkaline phosphatase, sodium, potassium or magnesium.

Acute and sub-acute paraquat poisoning in a pack of foxhounds.

A case of paraquat poisoning in a pack of foxhounds is reported. The incident provided a unique opportunity to compare residues levels of paraquat in dogs showing symptoms of acute and sub-acute poisoning. Paraquat was detected in the urine up to six days after exposure. A high performance liquid chromatography method for determining paraquat in tissue is described.