Transmission
Transferred by species of Tabanusflies, Trypanosoma evansi development does not take place in the actual vector. In order for the transmission to be successful, trypanosomes need to survive in the gut of the flies and be regurgitated during subsequent feeding. Since tabanidae are most abundant during rainy and post rainy seasons, that is when most outbreaks of Surra occur.
In order for the transfer of the disease from the flies to the animals, interruption of feeding habits needs to occur. This direct transmission technique involves them cutting the skin with their mouths, then lapping up the blood along with connective tissue fluid. This means a good indicator of disease would be looking at trypanosome density in capillary blood and connective tissue. After transferring the infectious organisms to the host species, the flies leave to rest and during that time transmission was successful only in some cases. Because the trypanosomes remain in the food canal of the flies for 4-8 hours depending on the species, the flies can feed off of one animal's blood more than one time, thus increasing the chance of successful transmission.
Although the most common method of transferring trypanosomes to other species is through tabanus flies, there are other insects that can also transmit this disease to livestock. These blood sucking insects are Stomoxys, Lyperosia, Hematopota, and Ornithordorus.
Other methods of transmission still being studied are looking at passing T.evansi thorough iatrogenic transmission. Evidence has been seen of transmission through sexual intercourse, through eating infected meat, and also through vampire bats in geographical areas where they are found.
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