THE TRANSMISSION OFBABESIA BOVISIN HERDS OF EUROPEAN AND ZEBU X EUROPEAN CATTLE INFESTED WITH THE TICK, BOOPHILUS MICROPLUS

Abstract

Transmission of Babesia bovis by the tick Boophilus microplus was studied in 4 breeding herds of European and Zebu x European cattle under different levels of tick infestation. The observations consisted of weekly counts of female ticks on the cattle, monthly serological tests for antibodies to B. bovis, examination of tick larvae from the pasture to determine B. bovis infection rates and comparison of the suitability of paddocks for tick reproduction. The rate of transmission (inoculation rate) was estimated in terms of the daily probability of infection and consisted of the product of the mean daily tick infestation head-1 and the babesial infection rate in tick larvae. The theoretical value of the minimum inoculation rate required to produce stability of babesiosis is 0.01. This value was exceeded only in a herd of European cattle with minimal tick control and grazing on a pasture favourable for tick reproduction. Instability of babesiosis occurred in the other herds of European cattle after tick numbers had been reduced by pasture spelling and strategic dipping and after reduction in the babesial infection rate in ticks apparently caused by unfavourable environmental conditions. Over a period of years, the tick infection rates also declined as a consequence of the reduction in numbers of ticks. The Zebu x European cattle failed to generate inoculation rates greater than the minimum level, even though no tick control measures were applied. This was attributed to lower babesial infection rates in the ticks than those observed in a comparable herd of European cattle and to the high tick resistance of the Zebu crosses which maintained the tick populations at low levels. Both factors combined to produce a low inoculation rate.

Seroepidemiology of bovine anaplasmosis and babesiosis in Venezuela

“…Although only a third of the total cattle population surveyed demonstrated antibodies to B. boris few clinical cases of babesiosis due to B. boris infections are reported in native animals. Perhaps enhanced tick resistance (Mahoney, Wright, Goodger, Mirre, Sutherst and Utech, 1981) or a genetically based immunity to B. boris characteristic of the zebu crosses act to affect low inoculation rates of this Babesia parasite.…”

Effect of breed of cattle on transmission rate and innate resistance to infection with Babesia bovis and B bigemina transmitted by Boophilus microplus

“…Mahoney et al 38 compared transmission of B bovis in B taurus and in three-eighths to half B indicus crossbred cattle in southeast Queensland and concluded that, in an enviro n m e n t u n f a vourable for tick surv i val, stocking with cro s s b red cattle will over several seasons almost lead to the disappearance of the ticks. However, our results show that if such cattle are moved to a paddock with a high B microplus infestation, Babesia transmission rates can be very high.…”

Serological evidence of exposure to tick fever organisms in young cattle on Queensland dairy farms

“…Herds with > 75% seropositivity were considered to be endemically stable (Stable herds). 19.54, P < 0.001). There was no significant difference in the likelihood of endemic stability between regions for A marginale (Chi-sq 5.02, P = 0.17).…”

“…The prevalence of infection among ticks feeding on Bos indicus cattle is even lower. 18,19 B bigemina therefore infects more cattle as calves because of this higher infection rate in Boophilus microplus compared to B bovis. 18 This was reflected in our study by a tendency for greater odds of endemic stability to B bigemina than B bovis in all decision to leave a few ticks on cows remained a significant term only in the model for anaplasmosis.…”