Theileriosis due to Theileria annulata is a major health hazard in crossbred cattle causing great economic loss to dairy industry in India. Zebu cattle and buffaloes, though exhibit presence of the parasite in blood, are resistant to T. annulata (Bansal et al. 1977). In the present communication, attempts have been made to analyse and correlate the haematological parameters and the parasitaemia with T. annulata in naturally infected cattle and buffaloes of the project area of the Mysore Milk Producers' Union (MMPU) of Karnataka State.

Samples of whole blood/blood smears from cattle (90% crossbreds) and buffaloes, mostly suffering from pyrexia, were collected or received through the veterinary officers of the MMPU as well as the Department of Animal Husbandry & Veterinary Services. They were processed in the laboratory for the identification of haemoparasite(s) as well as for haematological studies. Of 4,521 blood smears of cattle examined, 798 (17.65%) and out of 525 buffaloes examined, 38 (7.24%) had T. annulata infection. Total erythrocytes counts (TEC n=138), haemoglobin (Hb n=656), total leucocyte counts (TLC n=218) and differential leucocyte counts (DLC n=761) of varying number of positive cases depending on type of samplesreceived, were estimated following standard procedures (Schalm et al., 1975). The percentage of infected erythrocytes (parasitaemia) was expressed as + (scanty upto 2%), + + (mild 2 to 10%), + + + (moderate 10 to 40%), + + + + (high 40 to 60%) and + + + + + (very high > 60%) after examining 300 erythrocytes from 5-10 different microscopic fields under oil immersion lens.

Of the 656 infected cattle, 79.88 per cent had lower (+ and ++) and 20.12 per cent had higher (+ + + to + + + + +;) grades of parasitaemia. In spite of having lower grades of parasitaemia, the Hb level was appreciably reduced to <8 g per cent in 31.39 per cent cattle while the corresponding decline in Hb was recorded only in 15.54 per cent in higher grades. The result indicated that cattle with lower grades of infection suffered most. Another analysis of data related on Hb and TEC levels showed that Hb concentration >8 g per cent and the TEC > 4 m/cu mm levels were maintained by 45.11 per cent cases whereas 34.58 per cent cattle had Hb and TEC levels below these ranges.

From the results, it is clear that the prevailing parasitaemia and the severity of anaemia were found not proportional in about one-third cases. Disintegration of erythrocytes resulting in haemoglobinuria and consequent anaemia as observed in babesiosis, rarely occurs in theileriosis since no multiplication of parasites takes place in erythrocytes. Therefore, it is considered that anaemia is caused by factor other than direct destruction of erythrocytes by parasites. Alteration in the antigenicity of erythrocytes due to the entry of parasites, evokes an autoimmune reaction in the body which triggers the removal of infected erythrocytes from circulation by macrophages (erythrophagocytosis) causing anaemia (Schroeder and Ristic, 1968; Hooshmand-Rad, 1976; Dhar and Gautam, 1979;Lai and Soni, 1983; 1985). Lowered TEC and Hb values causingmacrocytic hypochromic anaemia was reported in cattle having T. annulata infection (Setty, 1969; Dhar and Goutam, 1979;Venugopal, 1983). However, Chengalva Rayalu and Hafeez (1995) recorded positive correlation between the decrease in TEC with the intensity of infection and observed macrocytic normochromic anaemia. In the present investigation, haemoglobinuria was noticed in a few cases as observed by earlier workers (Narasimha Murthy et al., 1968;Gautam et al., 1970).

Analysis of TLC had shown the presence of leucocytosis in 19.72, leucopenia in 6.88 and tendency towards leucopenia in 47.71 and normal count in 25.69 per cent of infected cattle. However, according to Barnett (1968), leucopenia was not observed in T. annulata infection in cattle. DLC indicated that 44.94 per cent had lymphocytosis, 1.71 per cent monocytosis, 16.69 per cent neutrophilia, 4.21 per cent eosinophilia, 2.22 per cent with combination of any of the above conditions and the rest 30.23 per centhad counts within normal range. Local cattle (n=71) showed high leucocytosis without appreciable changes in DLC. Various haematological values of buffaloes (n=38) positive for T. annulata indicated normal TEC with slight decrease in Hb values, besides the occurrence of leucocytosis with neutrophilia.Sharma et al. (1985) reported significant fall in TEC and Hb values with lymphocytosis and neutropenia in infected Murrah buffaloes in Vietnam. As pointed out by Al-Kushali et al. (1981), considerable variation in the haematological values of different cases were also observed in the present study and prognosis was predicted to be grave in those cattle that showed very low Hb and TEC values.

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