Failure of the Amblyomma cajennense nymph to become infected by Theileria equi after feeding on acute or chronically infected horses.

This study investigates whether the nymph Amblyomma cajennense tick can acquire infection from Theileria equi, a parasite causing tick-borne diseases in horses, by feeding on infected horses. The research found no evidence of tick infection from three different horse conditions – experimentally, naturally, or chronically infected.

Research Background

• Theileria equi and Babesia caballi are protozoan parasites found within red blood cells. They cause tick-borne diseases in horses, particularly in areas where these parasites are prevalent such as Latin America.
• The vector, or the entity responsible for transmitting this disease in the New World region, is still a controversial subject. This research aims to uncover whether the nymph stage of the Amblyomma cajennense tick is capable of being infected by T. equi, and thus potentially serving as a vector.

Methodology

• Three different types of horse infections were studied – experimentally infected, naturally infected foals, and chronically infected adults.
• The adult A. cajennense ticks that fed on these horses were dissected and their salivary glands collected.
• The salivary glands were stained with methyl green pyronin, a technique used to detect the presence of Theileria infection, which typically causes cell nuclei to enlarge.
• The presence of Theileria DNA was tested using nested PCR assays, a highly sensitive method of detecting small amounts of DNA.
• Finally, histopathological analysis was performed to identify sporoblasts and sporozoites of T. equi – developmental stages of the parasite – in the tick’s salivary glands.

Results and Conclusion

• There was no observed hypertrophy (enlargement) of the tick’s salivary gland acini or cell nuclei under pyronin staining, suggesting absence of Theileria infection.
• No Theileria DNA was detected in the PCR assay.
• Following histopathological analysis, no sporoblasts or sporozoites were found in the salivary gland acini.
• Based on these observations, the study concludes that the nymph Amblyomma cajennense tick does not become infected from feeding on T. equi infected horses, and thus may not play a significant role in transmission of this parasite.