Detection of natural infection of Boophilus microplus with Babesia equi and Babesia caballi in Brazilian horses using nested polymerase chain reaction.

The research studies the role of Boophilus microplus—a type of tick—in naturally transmitting Babesia equi and Babesia caballi parasites to horses in Brazil. Using a nested polymerase chain reaction (PCR) technique, the researchers discovered that the parasites’ genetic material is largely present in a range of samples, including the horse’s blood and different stages of the tick, further suggesting the role of B. microplus as a transmission vector.

Objective and Study Design

• The researchers aimed to verify the role of Boophilus microplus (B. microplus) ticks as natural vectors transmitting Babesia equi and Babesia caballi parasites to horses in Brazil. For this, they employed a nested polymerase chain reaction (PCR) technique to establish the presence of specific gene fragments of these parasites in different samples.

Methodology and Findings

• The researchers detected a 218bp gene fragment unique to B. equi in approximately 96% of horse blood samples and in 45.3-62.5% of female ticks, their eggs, larvae, and nymphs drawn from 47 horses.
• They simultaneously detected the presence of a 430bp gene fragment specific to B. caballi across horse blood samples and all stages of tick development, with the only exception being the partially-fed female ticks.
• In all examined samples, the presence of B. equi DNA was more prevalent than B. caballi DNA, with no samples testing positive solely for B. caballi.

Implications

• While prior experiments and ultrastructural studies in Brazil hinted towards B. microplus being a vector for B. equi and potentially B. caballi, this study provides molecular evidence supporting this notion. The wide presence of their DNA across tick stages and the horses’ blood is indicative of the tick’s role as a transmission vector.
• The researchers discovered B. equi and B. caballi DNA in the eggs and larvae of B. microplus. This implies a possibility for transovarial and transstadial transmissions—meaning, the parasites may be transferred vertically from the mother tick to her offspring, and could be sustained across the tick’s developmental stages, respectively.
• The PCR technique exceeded the detection capabilities of the Giemsa-stained thin blood smear method, highlighting its efficiency. Evidencing this, only 32% of blood smears returned positive results for Babesia parasites compared to nearly 96% accuracy with the PCR.