November 19, 2021

Treating Haemonchus contortus

My name is Rachel Conway, and I am a current fourth year veterinary student at Colorado State University, set to graduate in May 2022.

One of the first things I learned about when I got to Fossil Rim in August was about the parasite problem with several of their antelope species. The bug of biggest concern was a parasite called Haemonchus contortus, a roundworm that lives in the gastrointestinal tract.

While certainly not something most people considered flashy or interesting, it caught my attention because it was something that was extensively discussed in my classes and clinics at Colorado State- it’s a very common parasite in domestic sheep and goats. For some reason, it really surprised me to learn it was also such a pest for these amazing African antelope species as well. It highlighted to me how translational many aspects of veterinary medicine are once you have the basics.

The image contains Roan antelope are one of several species of ruminants housed at Fossil Rim that can be affected by Haemonchus worms.
Roan antelope are one of several species of ruminants housed at Fossil Rim that can be affected by Haemonchus worms.

With that said, anti-parasitic treatments and management of this problem has been an interesting challenge the veterinary and animal care staffs have faced throughout my time here, and was something I had wanted to discuss since it has been such a team effort that they take on almost on a daily basis.

Haemonchus is a type of what is called a nematode, or roundworm parasite. This parasite inhabits the gastrointestinal tract of many different ruminant species. Ruminants are a group of animals that have a specific type of gastro-intestinal tract, and include animals like domestic cows, sheep, goats- and many of the antelope species of Fossil Rim everyone loves to come and see.

These animals all have in common the famous “four stomachs” of cows. It’s actually not four stomachs, but one stomach with four parts- three of which are referred to as “forestomachs”- one can start to see where things got confused. These first three parts are fermentation chambers, where bacteria live and help these animals digest all the tough grass and forage that they consume. The last stomach, the abomasum, is the “true stomach” and is the part most similar to what we think of as a stomach. This is where the chemical digestion happens that helps us break down food to the point that our small intestine can absorb it into our body.

Its also where the little Haemonchus parasites make their home. This is a big problem for the animals they inhabit for a couple of reasons. As part of their life cycle, they burrow into the stomach lining, disrupting the function of the stomach to mechanically break up food, and to secrete enough acid to properly digest the food before it moves into the small intestine to be absorbed. This leaves the animal with a limited ability to properly absorb nutrients, and can cause a drop in weight. Even more problematic, these parasites as adults bite into the stomach lining and feed on blood vessels, causing many animals to become anemic, or have low levels of red blood cells. With these combined, you get thin, weaker animals as they can’t get enough nutrients, and their tissues can’t get good amounts of oxygen with such low red blood cell counts.

The image contains a gemsbok  under anesthesia with three vet and animal staff who will be administering an oral deworming drug.
Some animals can be treated with anti-parasitics by dart, but others will need a hands on exam, like this gemsbok who will be receiving an oral deworming drug.

How does the team at Fossil Rim combat this problem? By working all together. The vets determine who needs treatment based on what is called fecal egg counts in the animal’s poop. The worms living in the abomasum lay their eggs in the abomasum for the animals to pass through the rest of their digestive tract to poop out- where they hatch in the grass, climb up the blades of grass to be consumed by the animal, to deliver more worms back into the abomasum and complete the cycle. So if you look in the poop for parasite eggs, you can get an idea of how many worms are living in the animal. How do the vets get all these samples they need? They have the Animal Care staff help them out. The Animal Care staff work hard to collect samples for each individual antelope in the pastures, which are then processed by the veterinary technician, and measured a Modified McMasters Fecal Egg Count procedure to determine the parasite load. If it is above a certain level, the animal gets a dose of antiparasitic drug to help reduce the parasite numbers, and get the animal feeling better.

While it used to be as easy as dosing with an anti-parasitic drug, unfortunately over time resistance has been developing in these parasite populations, making the drugs less effective. So, in addition to anti-parasitic drugs, the Fossil Rim team has worked together to employ a variety of strategies as simple as good pasture management to as strange as parasite- trapping fungi safe for the animals to consume. All of these together have helped lower the parasite loads within the herds.

Why I decided to share this story was because it highlighted one of my favorite aspects of working here at Fossil Rim- how well everyone works together to help all the many animals that live here. I have absolutely loved being at Fossil Rim, and getting to work with such a great and knowledgeable team. I look forward to applying everything I’ve learned here to my future rotations and career in zoo and wildlife medicine.

-Rachel Conway, Veterinary Preceptee


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