Enhanced immunity to Hyalomma anatolicum anatolicum ticks in cross-bred ( Bos indicus × Bos taurus) calves using ascaris extract immunomodulator with the tick salivary gland extract antigens

Development of acquired immunity in cross-bred ( Bos indicus × Bos taurus) calves against Hyalomma anatolicum anatolicum, a tick vector of bovine tropical theileriosis was studied using ascaris extract (AE), an immunomodulator of IgE responses, along with the tick salivary gland extract (SGE) antigens in Freund's incomplete adjuvant (FIA) emulsion. Calves immunised with SGE + FIA showed significant rejection (47.4 ± 2.8%) of larvae, whereas only marginal rejection (12.47 ± 1.5%) of nymphs was observed. In contrast, calves immunised with the immunomodulator AE in addition to SGE + FIA showed significant enhanced rejection of nymphs (50.25 ± 5.2%), while the rejection of larvae was only slightly higher (55.8 ± 11.4%), and not statistically different. In addition, incorporation of the immunomodulator AE also resulted in significant enhancement in the percentage recovery of abnormally fed larvae and nymphs. This abnormal feeding was characterised by their white to pale-yellow colour insted of the dark-grey colour of normally fed ticks. It may possibly be attributed to their inability to gain access to the blood vessels owing to the host immunological reaction at the bite sites. Consequently, the ticks fed on extravascular fluid devoid of red blood cells resulting in their white to pale-yellow colour. Difference in the disease transmission potential of normally and abnormally fed ticks is of future interest. Sera from all the immunised calves after 2 weeks of immunisation were positive for anti-tick SGE antibodies in the dot enzyme immunoassay (DOT-EIA). The immunised calves were positive for immediate type hypersensitivity (ITH) skin reaction on intradermal inoculation of the tick SGE antigens. There was no apparent difference in the DOT-EIA antibody titres between the two immunised groups. However, ITH skin swelling was significantly higher in AE + SGE + FIA immunised calves. The study indicates that use of the AE as an immunomodulator along with the tick SGE antigens enhanced anti-tick immunity.