Scientists investigate anticoccidial drug efficacy

Study could bring major advancements in controlling coccidia in cattle production.

University of Wyoming assistant professor Berit Bangoura is working on a pilot study designed to deliver "important insights into the efficacy of anticoccidial drugs used every day in the U.S. cattle industry," according to an announcement from the university.

Bangoura explained that cattle face many infectious diseases, and parasites are a "very important group of disease agents. Effective antiparasitic drugs help agriculture by keeping animals healthy and production economically successful; however, most of the active ingredients have been used for decades, leaving parasites plenty of time to develop mechanisms to survive treatment."

Besides resistance shown in parasitic worms and insects, she noted that unicellular parasites, such as protozoa, adapt easily to heavily used drugs.

Coccidia are protozoa that represents a cluster of parasites that harm livestock, including cattle, sheep, goats, poultry and rabbits, Bangoura said. Coccidia mostly reside in the gut of one specific animal species and damage the gut mucosa. Especially in young animals, these parasites provoke diarrhea, fluid and weight loss and reduced animal growth and can cause death, she added. Once fully developed in surviving animals, the parasite is excreted with feces and is ready to infect the next host by feed contamination.

In cattle, coccidia are seen on nearly all farm operations, Bangoura said, noting that there are no recent investigations on the prevalence of cattle coccidia in the U.S. However, she said studies from Europe show that up to 95% of calf-rearing farms struggle with coccidia. Calves, heifers and young steers are most prone to the related disease called cattle coccidiosis.

According to Bangoura, the cattle industry relies heavily on chemical drugs (anticoccidials) to alleviate the animal health and financial implications of coccidiosis. However, the four anticoccidials currently available on the U.S. market have been sold and used for up to 50 years, she said, which implies that parasites are under constant treatment pressure not only in the U.S. but worldwide and may develop resistance.

Bangoura reported that no studies are available that investigate the level of drug efficacy against coccidia. She said studies in chickens show that coccidia can develop resistance within a few years, and there are many widespread, multi-drug-resistant strains in poultry.

How widespread is resistance?

In light of these field findings and the known economically threatening scenario in chickens, Bangoura said her team developed a plan to investigate the resistance situation in cattle coccidia. The team developed the following major questions driving the research:

* Are these bovine parasites already resistant against our few available anticoccidial drugs?

* How widespread is the resistance, and is there any drug that should be preferably used?

She said the research team asked cattle producers in Wyoming and Colorado to answer standardized questions regarding their management and husbandry conditions as well as the farm history of anticoccidial treatments.

They visited farms of those willing to cooperate and collected fecal samples from different age groups of young cattle. The feces were analyzed for coccidia, and positive samples were stored and the parasites purified from the fecal matter. The coccidia were passaged through calves to obtain enough material to conduct the drug resistance testing.

Bangoura explained that the recovered parasites from various field strains are the starting point for the following investigations. Although not yet completed, the first important step is developing a suitable cell culture readout assay that can serve as the basis for the drug resistance assessment in cattle coccidia, she explained, adding that no such test system is known to be available at other laboratories. "By establishing this assay, we look forward to gathering significant data on the drug resistance situation using modern parasitological tools," Bangoura said.

Collected cattle coccidia

The study design includes infecting the bovine cell cultures with the collected cattle coccidia strains, Bangoura said. In the cell culture setup, the parasites will invade the bovine cells and start to multiply within them, just as they would in the gut of young cattle.

"We can develop an assay to test drug efficacy without the need for extensive animal experiments. The cell cultures are grouped in parasite-infected, untreated cultures that allow the parasites to multiply without limitations and infected and drug-treated cultures," she said.

From the control cultures, the researchers can measure the parasite number formed in a given time if optimal conditions exist, Bangoura said. In the other cell cultures, parasites are challenged with the different drugs and expected to grow and multiply much less if the drugs are effective. In the end, the genetic material from each cell culture will be isolated and tested, she said, noting that the researchers would then be able to calculate the number of parasites per treatment group and know if the treatment was able to reduce the parasite growth significantly.

Drug resistance is indicated if the treatment did not lead to highly reduced parasite numbers in the cultures, Bangoura said, adding, "We will be able to tell if there are resistances and how widespread they are; in other words, how many different field strains of coccidia from Wyoming and Colorado are affected?"

Right treatment for specific strain

According to Bangoura, any detected resistances would strongly confirm prior findings of lacking drug efficacy in the field and would have a great impact on cattle farming.

Farm-specific advice on the most suitable anticoccidial drug would not only be necessary but available once the new assay is validated, she said.

"Our hope is the study brings major advancements to controlling these harmful parasites. Nonetheless, now is the time to address the ever-present challenge of coccidiosis in cattle rearing on an evidence-based treatment regimen instead of fostering resistance development by untargeted drug use," Bangoura concluded.