Biomedical subjects
Publications and source records attributed to R W Worthington.
The important viral, protozoal and bacterial diseases of wild African ruminants are reviewed. Special attention is paid to the epidemiological factors that determine the role played by these animals in the transmission of diseases to domestic stock. Examples of the converse situation where livestock serve as a source of infection for wild ruminants are also given.
Skin test antigens for the diagnosis of brucellosis were produced from the rough Brucella abortus strain 45/20. The production of two products termed Brucellin B and Brucellin W are described. The method described for the production of Brucellin W is recommended as an improved practical method of Brucellin production. The Brucellin products described were equal in sensitivity to that of a commercially available product, Brucellergen, which is used in New Zealand. Brucellin B was extensively tested in non-infected cattle and its specificity was equal to that of Brucellergen. Recommendations for the standardisation of skin test reagents for the diagnosis of brucellosis are made. Intradermal testing for brucellosis in cattle should be used only for the identification of infected herds and not as an individual animal test.
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The serological response to Brucella ovis and the shedding of the organism in semen was followed for a period of 13-14 months in 42 naturally infected rams. Most rams remained chronically infected and excreted the organism in their semen throughout the investigation. B. ovis was isolated from 87.9% of the semen samples from the infected rams. The most common sites from which B. ovis could be isolated at necropsy were the epididymides and accessory sexual glands. In one ram the organism was isolated from lung, spleen, kidney and iliac lymph nodes. Three rams ceased to shed B. ovis in their semen during the course of the investigation. Seventy-five (11%) of 686 sera from infected rams were negative in the complement fixation test (CFT) although 76% and 77% of CFT-negative sera were positive in the gel diffusion precipitin test (GDT) and enzyme labelled immunosorbent assay (ELISA) respectively. The high incidence of CFT-negative infected rams was due to the selection for the investigation of many rams with histories of negative or vacillating CFT titres. Sera from five rams which never shed B. ovis in their semen reacted erratically in the three serological tests. The five rams were from heavily infected flocks and were kept in contact with infected rams throughout the investigation.
The complement fixation test (CFT), the enzyme labelled immunosorbent assay (ELISA) and the gel diffusion precipitin test (GD) were compared, for the diagnosis of Brucella ovis infection in rams. The sensitivities of the tests in 109 rams which were shedding B. ovis in their semen were: CFT 96.3%; ELISA 97.2%; GD 91.7%. The specificities of the tests in 141 rams from non-infected flocks were: CFI 99.3%; ELISA 98.6%; GD 100%. Predictive values of the three tests were measured in 285 rams from infected flocks. Thirty-eight percent of these rams were shedding B. ovis in their semen. Predictive values of positive tests were: CFT 75.5%; ELISA 66.7%; GD 72.5%. Predictive values of negative tests were: CFI 97.1%; ELISA 97.6%; GD 93.8%.
The importance of correct interpretation of serological test results, common sources of error and problems associated with tests are discussed. In bovine brucellosis, a disease which is ideally suited to serological diagnosis, foetal contact with infection may cause the calf to be a serologically negative carrier. The immune tolerant animal resulting from foetal contact with virus is a major problem in the serological detection of border disease. In Johnes' disease and to a lesser extent in Brucella ovis and leptospiral infections, problems associated with sensitivity and specificity of the tests are stressed. Serovar specificity, cumbersome test procedures and negative tests in the incubation period cause difficulty in the interpretation of serological test results for leptospirosis. The importance of clinical examination, herd histories and alternative diagnostic procedures is important in all diseases. Wherever possible, flocks or herds should be maintained in specific disease-free state. Selection of stock from accredited herds or flocks is the most certain method of buying non-infected animals.
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Injection of Clostridium welchii (C. perfringens) type D epsilon toxin into sheep caused large increases in catecholamine and cyclic adenosine 3',5'-monophosphate levels and moderate increases in cyclic guanosine 3',5'-monophosphate levels. Haemoconcentration also occurred. It is suggested that a rapidly developing brain oedema is the stimulus for a release of catecholamines which in turn activates adenyl cyclase. The resulting rise in cAMP causes glycogenolysis and hyperglycaemia.
Heat-stable enterotoxins from a bovine and porcine strain of Escherichia coli were isolated and showed significant differences in amino acid composition and heat stability.
Heat-stable enterotoxins (ST-124 and ST-1261) have been isolated from two different enterotoxigenic Escherichia coli of bovine (124) and porcine (1261) origin. The enterotoxin preparations were isolated by ultrafiltration and ion-exchange chromatography and were both active in the suckling mouse test and pig ligated loop test in the nanogram range. The bovine (ST-124) enterotoxin was not stable to heating in its isolated form, and significant differences in amino acid composition were observed between the two enterotoxins. Although both toxins were active at similar levels in the suckling mouse and pig ligated loop tests, ST-124 lacked the ability to cause the profound secretory responses seen with ST-1261 in the weanling pig ligated loop.
Antibodies against epsilon toxin were isolated from hyperimmune horse serum by affinity chromatography. Purified epsilon prototoxin covalently bound to Affigel 202 was used as immunosorbent, and antibodies were eluted with 6.0 M guanidine chloride. In a single run 80 mg of antibody could be recovered from a 20 microliter column of immunosorbent. The antibody was shown to belong to the IgG(T) class of immunoglobulins.
Enzymatic activation of Clostridium perfringens epsilon prototoxin removed a small basic part of the molecule, causing a slight change in molecular weight (32,700 to 31,200) and a large change in isoelectric point (from pH 8.02 into fractions of 5.36 and 5.74).
It was shown that Clostridium perfringens epsilon toxin has the effect of allowing the passage of 125I polyvinyl-pyrrolidone and 125I human serum albumin into mouse brain. These substances did not enter the brains of normal control mice. The passage of albumin into the brains of mice poisoned with epsilon toxin was extremely rapid. When large doses of toxin (+/-4 000 MLD) were given death ensued within 2-3 min at which stage 1,5% of the injected albumin had already entered the brain. In cases where smaller doses were given and the time interval between injection and death was longer the figure was increased to 2-2 1/2% of the injected plasma albumin.
An attempt was made to purify Clostridium perfringens Beta toxin. Crude toxin prepared by ammonium sulphate precipitation of culture supernatants was purified by chromatography on Sephadex G50, Sephadex G100 and DEAE cellulose. This material, although highly purified was not homogeneous on polyacrylamide gel electrophoresis. It had a toxicity of 800 000 mouse MLDs/mg N, a typical protein absorption spectrum in the UV region, an iso-electric point of 5, 6 and the main component had a molecular mass of 42 000 +/- 2 000 (estimated by electrophoresis in sodium dodecyl sulphate containing polyacrylamide gels).
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