EPIDEMIOLOGICAL AND GROSS PATHOLOGICAL STUDIES OF ONCHOCERCA GIBSONI INFECTION IN CATTLE |
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| Authors: | PW Ladds S Nitisuwirjo ME Goddard |
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| Institution: | Department of Tropical Veterinary Science, James Cook University, Post Office, Queensland 4811 |
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| Abstract: | SUMMARY A total of 5712 cattle from 62 properties or localities in northern, central and eastern Australia were examined at abattoirs, and the presence of Onchocerca gibsoni infection was related to region, season when slaughtered, and breed, sex and age of slaughtered cattle. Additionally, these features were also related to nodule characteristics determined from macroscopic examination of all nodules in single (left or right) briskets from 1287 infected cattle selected at random from those examined in abattoirs. Infection rate was 86% and number of nodules per brisket was 3.7 ± 4.1 (Mean ± Standard Deviation). When adjusted for other variables infection rates varied from 18% in central New South Wales to a maximum of 96% in north western Queensland. Number of nodules per brisket in cattle from north western Queensland was 9 times greater than in cattle from central New South Wales. Most nodules (70%) were 1–2 cm in diameter and weighed less than 2 g. The occurrence of changes such as calcification and caseation indicated that 20–30% of nodules studied were undergoing advanced degeneration or resolution. More nodules were detected in autumn than during winter or spring and the proportions of nodules which were hard on palpation, or had thick capsules, both increased during the autumn-spring interval. Although inconclusive, breed differences observed suggested that Bos indicus and B. indicus crossbreds had slightly greater resistance to O. gibsoni infection than cattle of British breed. Infection rate and number of nodules per brisket were greater in bulls than in cows or steers but weight of nodules in steers was greater than in other groups. Percentage of animals infected, and nodule prevalence both increased with increasing age but annual increase in nodule prevalence was less in cattle over 5 years than in younger ones, suggesting development of some immunity in mature cattle. |
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