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This article was published in 1981
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Eperythrozoonosis in Sheep
I.R. Littlejohns, B.V.Sc., Veterinary Research Station, NSW Dept. of Agriculture, Glenfield
The main happening relating to Eperythrozoonosis in the last year has been an evaluation of the Coombs test as a diagnostic aid. A capacity for this test was established several years ago after John Archer enquired into the causes of jaundice in lambs at slaughter and found Eperythrozoonosis to be the major factor. Because some of the findings did not fit the acknowledged pathogenesis of the disease too well there was an interest in establishing ante mortem diagnosis; hence the Coombs test.
While no further work has been done on the abattoir problem, the Coombs test has been applied, together with microscopic examination of blood smears, for diagnostic purposes. Results were very variable with correlation between the two techniques being very good on occasions and apparently absent on others.
To evaluate the test, observations (PCV, Coombs and microscopic) were made weekly on 24 sheep (12 mature, 12 lambs) at pasture over about 10 months and then continued on 6 (3 of each age) after experimental inoculation with Eperythrozoon ovis infected blood.
In our hands, false positive Coombs tests occurred in a sporadic pattern in about 3% of samples. After infection the test was no more sensitive than microscopic examination and rather less reliable. It has therefore been shelved as a diagnostic procedure for Eperythrozoon ovis infection.
The capacity to do Coombs tests will be retained and is available for approved investigational purposes.
1. For in-depth investigation of Eperythrozoonosis in the field. This would mean repeated or serial sampling of identified animals with opportunity to apply all available diagnostic techniques with a view to their further evaluation and to using them all to better describe the epidemiology and pathogenesis of the natural infection and disease.
2. To investigate disease other than Eperythrozoonosis. Recently there have been two occasions when unthriftiness and some poorly documented anaemia has occurred in sheep associated with near 100% Coombs test reactivity but no other evidence of Eperythrozoon ovis infection.