Did you know that whitetail deer can share diseases and parasites with your sheep and goats? Meningeal worm, also called brain worm and deer worm, is one of those parasites. It is not as frequently seen or spoken of as other parasite, but it can be deadly if not treated promptly and properly. Thus, it is important for sheep owners to be aware of it. You should be able to recognize the symptoms and know how to treat it in case it ever shows up in your flock.
Meningeal worm is endemic in most whitetail deer populations, and they are its target host. It rarely causes any symptoms in deer. Unfortunately, many other species grazing areas where deer have been can accidentally pick up this parasite. Llamas and alpacas are particularly susceptible and many camelid owners preventatively deworm their animals regularly. However this is generally not recommended for sheep and goats due to gastrointestinal parasite dewormer resistance issues.
So what is meningeal worm?
Meningeal worm is a round worm, Parelaphostrongylus tenuis. It completes its lifecycle in deer resulting in larvae being shed in the feces of infected deer. According to Cornell University up to 80% of whitetail deer are infected in endemic areas. So there is a pretty good chance if you have a lot of deer around, you probably have meningeal worm to worry about. It can accidentally infect a broad range of hooved species including sheep, goats, moose, elk, camelids, even horses and cattle occasionally.
As with other parasites understanding its life cycle is critical to understanding how to manage it.
In its desired host, the whitetail deer, this parasite lives on the meninges (the membranes covering the brain). It doesn’t cause any symptoms or an immune response. Female worms lay their eggs on the meninges. The eggs hatch into larvae. Then the larvae migrate through the bloodstream to the lungs where they are coughed up and swallowed. After passing through the digestive tract, the larvae are excreted in the feces.
Once the larvae have been excreted, they infect a variety of species of slugs and snails. They are ingested by or burrow into the foot of the slugs and snails feeding on the feces. Once inside the snails the larvae continue to develop. The life cycle is completed when deer accidentally consume the slugs and snails as they forage. They can also become re-infected when they consume plant material covered with the slime trails of infected snails. The ingested larvae then migrate from the stomach into the abdominal cavity and up the nerve tissue to the spinal cord. They ultimately return to the meninges where they mate and start the process all over again.
As you can imagine, its very easy for your sheep or goats to accidentally ingest the same slugs/snails and slime trails as deer.
Unfortunately when this happens things go a little haywire. Symptoms usually start to appear 30-60 days post ingestion. This means symptoms are typically seen late summer and early fall though they certainly can appear at other times of the year.
When ingested by an accidental host, the larvae attempt to start the same process as in deer. They migrate out of the stomach and into the nervous tissue of the abdominal cavity. However, at this point things go wrong. Unlike deer, who mount very little immune response, your sheep have a large immune response. This causes issues for the worms who get confused about where they’re going. Instead of migrating up through the nervous system, the worms end up burrowing around in the nervous tissue causing damage. The sheep’s immune response causes inflammation resulting in more damage.
This inflammation and nervous system damage create the symptoms you see.
Depending on where the damage is occurring the symptoms can vary. When the nerve damage is happening in nerves that aren’t in the spine, you get animals that are intensely itchy. They will often itch holes in themselves where the nerve damage is occurring. If the damage is occurring in the spinal cord you will see other symptoms. You may see things like minor lameness or stumbling on a rear leg, abnormal gait, incoordination, circling, head tilt, etc. If the worms reach the brain neurological symptoms may look similar to listeria or polio. The symptoms typically get progressively worse and can result in paralysis and death if left untreated.
Usually, the infected animals are bright and have good appetites. They do not appear ill aside from the above symptoms. It can be tricky to recognize symptoms, and they may even appear to recover briefly as the worms migrate through different parts of the nervous system. However, the symptoms typically reoccur, and prompt treatment is important as the nerve damage may become permanent.
There is no test for this parasite as the worm larvae is inside the nervous tissue and there are no eggs being shed in feces.
Diagnosis is made solely based on the symptoms and response to treatment. It is very important to treat meningeal worms using the correct deworming protocol. If you are treating for meningeal worm after symptoms have occurred, they are protected within the nervous system. Not all dewormers are capable of reaching them there. A few years ago Cornell did a study on a treatment protocol, and determined that meningeal worms can be most effectively treated using fenbendazole (Safeguard®) and Dexamethazone (or Banamine for pregnant animals) and ivermectin.
The recommended treatment protocol from Cornell University is to give:
- Safeguard® (10% Fenbendazole) orally for 5 days at 25 mg per kg of live weight
- Dexamethasone injectable 2 mg/mL IM at 0.2 mg/kg live weight for first 3 days and 0.1 mg/kg next 2 days. Ewes and does in last month of pregnancy are not to receive Dexamethasone. Instead, they will receive flunixin meglumine (Banamine® ) 50 mg/mL at the rate of 1 cc/100 lb live weight (1.1 mg/kg) orally for 5 days.
- Ivermectin 1% injectable administered SQ for 5 days at 0.5 mg/kg live wt. *It is thought that ivermectin can be a beneficial treatment, but significantly increases withdrawal times.
Keep in mind that this deworming protocol comes with a very long drug withdrawal period (90 days or more). The withdrawal times can change and vary from species to species. It is extremely important to verify and follow withdrawal times for any treatment that you use. If you are raising animals for meat, you must weigh the pros and cons of deworming vs. not. Many times symptoms appear late in the season when processing dates are not very far off.
If you have mild cases where there is just some itchiness in low value animals you may be able to manage the symptoms without deworming treatment. Sheep do mount an immune response to the worm and may be able to clear the parasite from their body themselves. However, treatment should be started promptly in severe cases or in valuable animals where you are not ok with the possibility of a wait and see approach resulting in euthanasia being necessary.
So is there anything I can do to prevent meningeal worm problems?
As you might expect, the answer is yes and no. The obvious answer is of course preventing deer and or snails from accessing the pastures where your sheep graze. Both are required to cause disease in your sheep. Unfortunately, that can be extremely difficult to execute. It takes months for the larvae to mature in the snails. This means that deer need to be excluded at all times, not just when your sheep are grazing. Plus, snails and slugs do not respect fence and can move into your pastures under fences.
However, there are things you can do to help prevent exposure. You can try to minimize deer on your grazing land through utilizing things like livestock guard dogs or fencing to repel deer. You can improve drainage and also avoid grazing wet areas that are heavily infested with snails. Though the infected snail and slug species are land snails, they do still require moisture, so if you can put snail repelling things like gravel roads devoid of vegetation between where deer graze and your pastures that can help too. Free ranging poultry may also help reduce your slug and snail populations.
Unfortunately, if you live in an endemic area and graze pasture, it is likely to be an occasional problem for you.
Therefore, it is wise to get good at recognizing symptoms. Then be sure to take some time to observe your flock daily. That way you can catch and treat infected animals early resulting in the best possible outcomes. And while you will likely always see a few cases in endemic areas, your sheep are capable of developing an immunity to the parasite meaning you will likely see fewer cases over time, particularly in your adult animals.
So as fall approaches this season, take some time to learn to recognize symptoms and observe your flock so that you can catch this parasite before it harms or kills any of your sheep.
If you would like to read more articles about keeping your flock healthy, please sign up for our newsletter to get our future articles delivered directly to your inbox!
Please remember
The information provided is for general informational purposes only. All information on the site is provided in good faith, for general informational and educational purposes only and is not a substitute for professional advice. We make no representation or warranty of any kind, express or implied, regarding the accuracy, adequacy, validity, reliability, availability, or completeness of any information on this Site. Accordingly, before taking any actions based upon such information, we encourage you to consult with the appropriate professionals. We do not provide any kind of professional advice. THE USE OR RELIANCE OF ANY INFORMATION CONTAINED ON THE SITE IS SOLELY AT YOUR OWN RISK. View full disclaimer here.
