Bovine tropical theileriosis, caused by Theileria annulata and transmitted by Hyalomma ticks, is one of the most economically devastating tick-borne diseases of dairy cattle and buffaloes in the Indian subcontinent. Over two decades of systematic research in Punjab, India, has generated foundational knowledge on the clinical, haematobiochemical, molecular, and epidemiological dimensions of this disease, with emerging insights into its phylogenetic diversity and transboundary significance. Early clinico-haematobiochemical studies on naturally infected bovines established the hallmark pathophysiological alterations associated with T. annulata infection, including anaemia, leucopenia, hypoproteinaemia, and derangements in serum mineral profiles, particularly in cattle. Subsequent outbreak investigations in Punjab revealed recurring disease clusters in cattle, with significant morbidity and mortality in dairy herds, highlighting the persistent enzootic challenge. Atypical clinical presentations, including cutaneous involvement and cerebral theileriosis, the latter molecularly confirmed for the first time in a crossbred cattle calf in India, were documented, emphasising the expanding clinical spectrum of the disease.
A cross-sectional molecular epidemiological study across five agro-climatic zones of Punjab, using PCR targeting the Tams1 gene, revealed an overall molecular prevalence of 32.99%, approximately 3.5-fold higher than microscopic prevalence (9.29%), confirming the existence of a substantial subclinical reservoir. Significant spatial heterogeneity was observed, with the highest prevalence in the central plain zone (43.94%). Cattle (35.01%) were significantly more susceptible than buffaloes (28.07%), with young calves (≤1 year) at highest risk. The simultaneous detection of T. annulata, Babesia spp., and Trypanosoma spp. by multiplex PCR underscored the reality of co-infections in field conditions. Comparative evaluation of molecular assays confirmed the superior sensitivity of PCR-based diagnostics over conventional microscopy for surveillance purposes.
Phylogenetic analysis of Tams1 sequences revealed 94–99% homology with global isolates, with Punjab strains showing closest genetic affinity to Iranian isolates, suggesting transboundary parasite movement rather than purely regional circulation. The genetic diversity observed indicates the co-circulation of multiple T. annulata genotypes within Punjab, with important implications for vaccine design. Collectively, this body of work, synthesised in a comprehensive review of bovine tropical theileriosis under the Indian scenario, underscores the need for integrated control strategies encompassing molecular surveillance, targeted acaricide use, and development of multivalent vaccines, within a broader One Health framework addressing transboundary disease risks.
