Cattle rabies vaccination--A longitudinal study of rabies antibody titres in an Israeli dairy herd

In contrast to many regions of the world where rabies is endemic in terrestrial wildlife species, wildlife rabies has been controlled in Israel by oral rabies vaccination programs, but canine rabies is re-emerging in the northern area of the Golan Heights. From 2009 to 2014 there were 208 animal rabies cases in Israel; 96 (46%) were considered introduced primary cases in dogs, triggering 112 secondary cases. One third (37/112) of the secondary cases were in cattle. Rabies vaccination is voluntary for cattle in Israel, except those on public exhibit. Rabies vaccination schedules for cattle vary based on farm practices and perception of risk. In this study 59 cattle from a dairy farm which routinely vaccinates against rabies were assigned into six groups according to age and vaccination histories. Four groups contained adult cows which had received one previous rabies vaccination, one group of adults had received two previous vaccinations, and one group was unvaccinated calves. Serum samples were collected and the cows were vaccinated with a commercial rabies vaccine. Sera were again collected 39 days later and the calf group re-vaccinated and re-sampled 18 days later. Sera were analyzed for the presence of rabies virus neutralizing antibodies using the rapid immunofluorescent antibody test. Cattle with antibody titres ≥ 0.5 IU/ml were considered to be protected against rabies. Twenty-six of 27 adult cattle (96%) vaccinated once at less than five months old did not have protective titres. Sixty percent (6/10) cattle vaccinated once at around six months of age did have adequate titres. Cattle previously vaccinated twice (n=10; 100%) with an 18 month interval between inoculations, had protective titres and protective antibody titres following booster vaccination (n=51; 100%). The anamnestic response of cattle to a killed rabies vaccine was not affected by the time interval between vaccinations, which ranged from 12 to 36 months. These results suggest that calves from vaccinated cows should not be vaccinated before six months old to avoid maternal antibody interference. Whilst most cattle older than six months old will be protected after a single inoculation, a second inoculation ensures a higher antibody levels for improved protection. Cattle receiving an effective priming dose responded well to a booster up to 36 months later. Such results demonstrate the effectiveness of rabies vaccination in cattle and the added value of a second dose to ensure a prolonged immune response against rabies.

Rabies virus detection by RT-PCR in decomposed naturally infected brains

The warm climate of Israel and mishandling of the cadavers during transit to the laboratory requires an accurate method for diagnosis of rabies in decomposed tissues. By using the reverse transcriptase polymerase chain reaction (RT-PCR) 10 decomposed brain samples that collected between 1998 and 2000 were diagnosed as negative by direct fluorescent antibody test (FAT), were found positive. Three of the 10 decomposed brains were confirmed as positive by isolation of rabies virus in tissue culture and by mouse inoculation (MIT) while the other seven decomposed samples were found positive only by RT-PCR. Direct sequencing and molecular analysis of a 328bp fragment of the N gene of all the rabies sequences confirmed their geographical origin. These results demonstrated the importance of the RT-PCR in the detection of rabies virus in decomposed naturally infected brains, especially in cases when the sample is not suitable for other laboratory assays. Thus, the RT-PCR can provide a positive diagnosis; however, when a negative result is obtained due to the nature of the decomposed tissue that can be caused by technical reasons and a false negative might be the case.