A Ten Year Prevalence Study of Marek's Disease and Avian Leukoses at Ibadan, Nigeria

Fatunmbi 0.0., D. F. Adene: A Ten year Prevalence Study of Marek's Disease and Avian Leukoses at Ibadan, Nigeria. Acta Vet. Brno, 55, 1986: 49-53. Diagnostic studies were undertaken on the prevalence of Marek's disease (MD) and Avian Leukoses (AL) between 1975 and 1984. Over the period, 22 cases of outbreaks of MD and 19 cases of outbreaks of AL were recorded. During this period, there were two noticeable peak incidence for MD in 1977 and 1983/84 while for AL there were three peaks in 1977, 1979 and 1983. It was observed that the lag period, from 1977 to 1983, when MD incidence remained low reflected the effect of the widespread application of MD vaccines in the advanced poultry producing countries which supplied the bulk of the Nigerian poultry. The importance of diagnostic surveillance of MD is discussed. Survey, diagnosis, local vaccination programmes. Marek's disease (MD), a lymphoproliferative neoplasm of domestic fowl caused by a herpes virus, was a major disease problem and source of great economic losses in poultry until the early 1970's. The discovery of the turkey herpesvirus lyophilised vaccine for MD in 1970, was followed with progress in the control of the disease (Okazaki et al. 1970; Purchase and Schul tz 1978). Although routine MD vaccination has to-day not been adopted in Nigeria, the poultry industry appeared to have benefitted from the spill-over effects of the vaccination standard and practices in the poultry exporting countries. For this reason and because of the pathological relationship between MD and Avian Leucoses (AL) which is another economicaIly important neoplasm of poultry, a diagnostic surveillance for both diseases has been maintained in our Poultry Disease Unit (PDU) at the University of Ibadan. This paper describes the studies on MD and AL from 1975 up to date, and discusses the trend in the incidence as -well as the possible implications of these observations on the epizootiology of MD. Materials and Methods Clinico-pathological studies: Carcasses submitted to our Poultry Disease Unit (PDU) originated mainly from Oyo State and occasionally from five neighbouring States namely Lagos, Ogun, Ondo, Kwara and Bendel. Each carcass was rountinely subjected to post mortem examination, paying attention to age of flock, changes in size, colour and the transectional appearances that might be suggestive of neoplastic growth in the major organs such as the liver, spleen and gonads. Two or more major peripheral nerves were additionally examined to differentiate between MD and AL as proposed by Goodchild (1969) and reviewed by Adene (1980). The period of ten years of study covered entries made from April 1975 to April 1984. From the later part of 1983, an unusual trend in the prevalence of neoplastic cases was observed at the PDU. It was therefore decided to subject one of them (Case No. 83/12/166) to additional investigation and test the accuracy of our post mortem diagnostic methods. In one such cases involving a 15 week old batch of pullets which originated from Oyo State, specimens of the neoplastic tissues and feathers from live birds were subjected to histopathology and sero-diagnosis, respectively. Histopathology: Samples of the liver, gonad and sciatic nerve were collected from Case 83/12/