Studies of Jembrana disease in Bali cattle

The clinical and haematological changes in experimentally induced Jembrana disease in Bali cattle (Bos javanicus) were described. The major clinical signs were an elevated rectal body temperature persisting for 7 days (range 5 to 12 days), lethargy, anorexia, enlargement of the superficial lymph nodes, a mild ocular and nasal discharge, diarrhoea with blood in the faeces, and pallor of the mucous membranes. Not all of these changes occurred in all affected cattle. The major haematological changes included a leukopenia, lymphopenia, eosinopenia and a slight neutropenia, a mild thrombocytopenia, a normocytic normochromic anaemia, elevated blood urea concentrations and reduced total plasma protein. The mortality rate in the experimentally-infected cattle was 17%. The infectious agent was shown to occur to a high titre of about 108 infectious doses per ml in the blood of Bali cattle during the febrile period of the disease, and to persist in cattle for 25 months after clinical recovery. Infection of other cattle species and buffaloes (Bubalus bubalis) resulted in a subclinical infection or milder clinical and haematological changes than detected in Bali cattle. Infection of Ongole cattle (Bos indie us), buffaloes (Bubalus bubalis) induced a mild febrile response after inoculation with the Jembrana disease agent but no other overt clinical signs of the disease. When 2 types of crossbred Bali (Bos javanicus x Bos indicus) cattle, and Friesian (Bos taurus) cattle were infected with the virus, some of these animals also developed lesions that were consistent with those detected in Bali cattle with Jembrana disease but the lesions were markedly less severe than in Bali cattle, and some changes that consistently occurred in Bali cattle, particularly haemorrhagic lesions and anaemia, were not detected. Sheep, goats and pigs did not develop any clinical signs after infection. Ongole, Ongole x Bali cattle, Friesian cattle, buffaloes and sheep developed a persistent infection after inoculation; the infectious agent persisted in blood or spleen for at least 9 months in buffaloes and for shorter periods in the other species. The properties of the infectious agent present in plasma of infected Bali cattle, that contained about 108 infectious agents per ml during the acute clinical disease, were determined. The agent was demonstrated by exclusion membrane filtration to be 50 to 100 nm in size, demonstrating the infectious agent was a virus and not a rickettsia-like agent as previously proposed. The virus exhibited characteristics of viruses in the family Retroviridae, including size (75-130 nm), morphology and morphogenesis of the virions in plasma and tissues from affected animals determined by electron microscopy, the density (1.15 g/ml) in sucrose gradients, and the presence of an intravirion reverse transcriptase. The morphology and apparent morphogenesis of the virions most closely resembled that of viruses in the subfamily Lentivirinae. Further evidence of the relationship of the virus to lentiviruses was the antigenic relationship of an immunodominant 26K protein of the virus to the 26K capsid protein of bovine immunodeficiency virus. The virus was designated Jembrana disease virus (JDV). An enzyme-linked immunosorbent assay (ELISA) was developed that detected antibody in Bali cattle against JDV. In experimentally infected Bali cattle, antibody was not detected in a majority of the cattle until 11 weeks after infection and a maximum antibody response was detected 23 to 33 weeks after infection. Antibody was still detectable in a majority of cattle 59 weeks after infection. A similar antibody response was also detected in nearly all crossbred Bali (Madura and Rambon) cattle that were infected with JDV although these types of cattle developed only a mild or subclinical infection. Clinical and pathological evidence that Jembrana disease occurred in cattle from Bali island, Lampung and West Sumatra provinces in Sumatra island, Jawa Timur (East Java) and South Kalimantan provinces but not in other areas of Indonesia was confirmed by the detection of antibody in cattle from these areas but not from other areas of Indonesia. Serological results also confirmed epidemiological evidence that there has been limited spread of Jembrana disease from endemic areas to adjacent areas. Studies of the methods of transmission of JDV were undertaken, with emphasis on the possible methods of contact transmission of the infection. The virus was detected in saliva, milk and urine of Bali cattle during the acute clinical phase of the disease. The disease was also induced in susceptible Bali cattle by ocular, intranasal and oral instillation of vims. As there has been limited spread of the disease from endemic areas to adjacent areas, and a higher prevalence of sero-conversion to JDV in cattle where there was close contact, it was hypothesized that the disease could be transmitted to susceptible cattle from vims in secretions when there is close contact between susceptible animals and animals with the acute disease. The possibility of transmission of the disease by mechanical transfer of blood from animals with the acute disease, wherein there is a high litre of virus in blood, by either blood sucking arthropods or during mass vaccination procedures involving the multiple use of a single needle and syringe, is also discussed