Veterinary Parasitology 101 (2001) 91–100 Impact of field vaccination with a Theileria annulata schizont cell culture vaccine on the epidemiology of tropical theileriosis S. Singh a , N. Khatri a , A. Manuja b , R.D. Sharma a , D.V. Malhotra b , A.K. Nichani b,∗,1 a Department of Veterinary Epidemiology and Preventive Medicine, College of Veterinary Sciences, Chaudhary Charan Singh Haryana Agricultural University, Hisar 125004, India b AICRP on Blood Protista, College of Veterinary Sciences, Chaudhary Charan Singh Haryana Agricultural University, Hisar 125004, India Received 22 March 2001; accepted 8 June 2001 Abstract Tropical theileriosis, caused by Theileria annulata, is an important tick-borne disease of cat- tle. A cell culture attenuated vaccine has been developed in our laboratory by long-term in vitro propagation of the schizont stage of the parasite. A longitudinal study was conducted at selected farms housing indigenous, cross-bred and exotic animals to investigate the effect of vaccination on the epidemiology of the disease. A total of 120 animals in 4 age groups were vaccinated with the vaccine before the onset of disease season. An equal number of age-matched animals were kept as controls at the same sites. Animals were monitored for 14 months at monthly intervals. The 97.5% vaccinated animals showed a rise in antibody titres 1 month post-vaccination, as de- termined by single dilution ELISA. The 78.3% of non-vaccinated animals became sero-positive over the period of observation. Mean antibody titres were significantly higher in vaccinated than non-vaccinated animals. Cross-bred animals showed higher antibody titres followed by exotic and indigenous animals in both the vaccinated and non-vaccinated groups. However, the antibody titres in animals of different ages were similar. The 36.7% vaccinated and 64.2% non-vaccinated animals became carriers (<0.5% piroplasms in erythrocytes) during the observation period. Clinical cases of theileriosis were recorded only in the non-vaccinated group suggesting that vaccinated animals ∗ Corresponding author. Tel.: +91-1662-37038; fax: +91-1662-37038. E-mail addresses: aknichani@hotmail.com, nichana@sask.usask.ca (A.K. Nichani). 1 Present address: 120 Veterinary Road, Saskatoon, Sask, Canada S7N 5E3. Tel.: +1-306-966-8874; fax: +1-306-966-7478. 0304-4017/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0304-4017(01)00502-7