Antimicrobial Agents and Infectious Diseases

Pig Parasite Becomes Resistant to Its Only Known Treatment

A Dutch isolate of the parasite Cystoisospora suis, that causes diarrhea in newborn and young piglets, has become resistant to toltrazuril, which is its only known treatment.  Even though this resistance is developing slowly, agricultural microbiologists at the Institute of Parasitology in Czechoslovakia led by Anja Joachim have said they will intensify their monitoring efforts and urge farmers to increase their hygiene measures to prevent the disease from spreading.  Once parasites appear on a farm, there is no way of permanently removing them.

Although the parasite is rarely fatal, it causes reduced body weight in suckling piglets and uneven weight development, which can produce significant economic losses for the farmers involved.  It also leaves the piglets more susceptible to serious swine diseases that can lead to the loss of entire litters.

Toltrazuril has been used against the parasite for the past two decades in Europe, and resistance was not observed until 2014 in Holland.  Researchers at the University of Veterinary Medicine in Vienna, Austria, took fecal samples from this farm, and confirmed through a series of studies that Cystoisospora suis had indeed become resistant.  Toltrazuril will kill Cystoisospora suis in the gut, but will also interfere with the production of oocytes, which show up in stool and are the final developmental stage of the parasite.  The researchers administered various doses of toltrazuril to an experimental cohort of piglets after they were infected with the isolate from the Dutch farm.  All the piglets developed diarrhea on the fourth day after infection, and all the fecal samples were positive for oocytes, even from pigs that had received a double dose of medication.

For more information, go to Parasites & Vectors; DOI: 10.1186/s13071-017-2257-7.