Infection with Babesia bovis alters metabolic rates of Rhipicephalus microplus ticks across life stages

Metabolic responses to infection differ based on arthropod and pathogen. Increased metabolic rates can result in faster depletion of energetic resources, and decreases may allow for energy conservation. Babesia bovis is a protozoan pathogen transmitted by the cattle fever tick, Rhipicephalus microplus. Adult female ticks acquire B. bovis by feeding on an infected animal. Babesia bovis undergoes development and invades the ovaries where it is transmitted transovarially to tick offspring. The effects of infection on R. microplus metabolic rate are not well studied.

We tested the hypothesis that R. microplus infected with B. bovis would have altered metabolic rates (volume of carbon dioxide [VCO₂]) across life stages using flow-through respirometry. Replete females from either an infected or naïve calf were measured across 3 days to determine differences in VCO₂. Hemolymph smears were used to categorize the number of B. bovis kinetes present in the hemolymph of replete females during egg oviposition. The VCO₂ for groups of their offspring were measured twice as eggs and once as larvae. The number of individuals and successfully hatched larvae in each group were enumerated at the end of the experiment to determine the average VCO₂ per individual.

Infected replete females have decreased VCO₂ while their offspring have increased VCO₂ at the egg and larval stages. Interestingly, replete females had a 25% reduction in body mass compared to uninfected female tick controls. Uninfected larvae were twice as likely to hatch than larvae from infected replete female ticks.

VCO₂ varied between control and infected ticks depending on life stage. Infected replete females had lower VCO₂ and body mass while their offspring had higher VCO₂ than their control counterparts. Higher larval VCO₂ may promote earlier questing and a shorter lifespan. Changes in metabolic and hatch rates have implications that may promote disease spread.