Study could bring major advancements in controlling these harmful parasites
Livestock such as cattle suffer from many infectious diseases farmers and veterinarians fight every day.
Parasites are one 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.
Resistances are shown in parasitic worms and insects but also unicellular parasites, such as protozoa, adapt easily to heavily used drugs. They deal with antiparasitics by changing their metabolism to evade the toxic drug effects.
One group of protozoa called coccidia represents a cluster of parasites that harm livestock including cattle, sheep, goats, poultry, and rabbits. 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. 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, we see coccidia on nearly all farm operations. There are no recent investigations on the prevalence of cattle coccidia in the U.S.; however, studies from Europe show that up to 95 percent of calf-rearing farms struggle with coccidia. Calves, heifers, and young steers are most prone to the related disease called cattle coccidiosis. Many farmers suffer immense financial losses due to coccidiosis.
Long-term effects like lower final adult body weight and prolonged increased feed costs occur in affected animals and herds. The cattle industry relies heavily on chemical drugs (anticoccidials) to alleviate the animal health and financial implications of coccidiosis. Unfortunately, all four anticoccidials available on the U.S. market have been sold and used for up to 50 years, and they are used every day on most cattle-rearing farms. That implies parasites are under constant treatment pressure not only in the U.S., but worldwide, and may develop resistance.
Interestingly, no study is available that investigates the current level of drug efficacy against coccidia.
Studies in chickens show coccidia can develop resistance within a few years, and we know that in poultry there are many multi-drug resistant strains widespread in the field.
Anecdotally, we know farmers are dissatisfied with the efficacy of the anticoccidial treatment they apply to young cattle. There may be many reasons contributing to reduced treatment effects, such as underdosing of the drug or a too-short treatment period; however, diagnostic fecal samples submitted from operations using a strict regimen of anticoccidial drug treatment often contain pathogenic coccidia, some in alarming amounts.
How widespread is resistance?
In light of these field findings and the known economically threatening scenario in chickens, we developed the plan to investigate the resistance situation in cattle coccidia. These are the major questions driving our 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?
We 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.
We visited the 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. They were passaged through calves to obtain enough material to conduct the drug resistance testing.
The recovered parasites from various field strains are the starting point for the following investigations. Though not yet complete, the first important step is the development of a suitable cell culture readout assay that can serve as the basis for the drug resistance assessment in cattle coccidia. 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.
Collected cattle coccidia
The study design includes the infection of bovine cell cultures with the collected cattle coccidia strains. 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 of 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.
From the control cultures, we can measure the parasite number formed in a given time if optimal conditions exist. 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. We can 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 we discover the treatment did not lead to highly reduced parasite numbers in our cultures. Such resistance will be examined for all available drugs. 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
This pilot study will deliver important insights into the efficacy of anticoccidial drugs used every day in the U.S. cattle industry. Any resistances detected would strongly confirm prior findings of lacking drug efficacy in the field and would have a great impact on cattle farming. Farmers would have to ensure the anticoccidial treatment they apply is the right choice for the coccidia field strains on their operations.
Farm-specific advice on the most suitable anticoccidial drug would not only be necessary, but available once our assay is validated.
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.
Author: Berit Bangoura, Assistant Professor, Department of Veterinary Sciences
To contact: Bangoura can be contacted at (307) 766-9959 or at firstname.lastname@example.org.