Session 2
Control of Intestinal Parasites in Camelids and Small Ruminants
Dr. Stephen Purdy, Executive Director of Animal Management, Center
for Agriculture and Director of Camelid Studies at the University of Massachusetts
Prevention is the key to intestinal parasite control. Overcrowding and poor sanitation must be addressed to overcome parasite infestations and to minimize the potential for reinfection. Parasite control programs must be able to be easily implemented. They must rely heavily on good management practices and lightly on use of drugs.
It is not possible, and it is not desirable, to remove all of the parasites from the herd/flock. A low level of parasites is important to keep the immune system stimulated. Intestinal parasites should be managed to avoid clinical disease through a combination of practices including:
- feces removal
- pasture rotation
- inter-species grazing
- lastly use of medication
Only 20% of the animals in a group harbor 70 to 80% of the parasites. Identify those animals, treat them only if absolutely necessary, and keep them away from the rest of the herd/flock. This latter phrase is especially true for young animals. They have a lower resistance to intestinal parasites because of their relatively immature immune systems. Remove animals with low resistance to parasites from the breeding herd/flock.
Good nutrition is the basis for being able to fight off any immune system challenge including intestinal parasites. It is very important to keep the herd/flock well fed with minimal competition for food. Rather than seeking a new medication to treat an intestinal parasite problem, start to investigate the management and housing situation. Most farms with large parasite problems are overcrowded and/or have underfed animals.
Periodic performance of fecal exams is the best way to investigate the level of parasitism in the herd/flock. Multiple methods of analyzing feces exist. It is important to use a consistent, easily performed technique. Fecal egg or oocyst count reduction test is performed by comparing levels before treating with a specific product with those measured 10 days after administering medication. If there is less than a 90% reduction in the egg per gram (EPG) or oocyst per gram (OPG) count, there is drug resistance! Individual sampling of all suspect animals should be done on those with poor body condition, poor growth rates, or those with diarrhea or loose stools. A herd/flock screening test should include approximately 25% of the animals in each group. Location for Checking BCS is on the back of camelids and small ruminants above the pelvis.
Strongyles are the most common intestinal parasites of camelids and small ruminants on most farms. Their eggs are passed in the feces and under the right conditions of temperature and moisture they hatch into larvae. The larvae mature into the infective L3 stage, which are found primarily in the lower 2 inches of the plants on pasture. Camelids and small ruminants get infected with parasites while consuming these plants. If we keep our pastures from getting overgrazed too short, then the infection rate will be low, so remove animals before all of the pasture is eaten down. Do not let the animals graze lower than 2-3 inches above the ground.
All strongyles have the same life cycle. Adults are in the GI tract of the ruminant. Eggs are passed in the manure. They eat, molt, eat, molt to infective stage in manure. It takes a week or more time in cooler weather. Larvae dispersed by rain and other physical means. They follow moisture films up and down grass blades. They die faster when the air is hot and dry. The adult worm life span is months.
Another important GI nematode is Haemonchus contortus or “Barber pole worm”. It Infects C3 / abomasum of the ruminant. It is a blood sucking parasite. This can cause these results: anemia (pale), bottle jaw, and eventually death! In 2009, the disease caused by Haemonchus was very severe. Haemonchus likes the warm, humid weather of 2009. It has a short life cycle, about 3 weeks from infection to egg laying. It is a prolific egg producer: 1 female Haemonchus adult can lay 5000 eggs/day!! Two hundred females produce up to 1 million eggs/day!! Mild winters extend the transmission season.
Other GI nematodes contribute to disease in ruminants, especially diarrhea. Ostertagia or the brown stomach worm resides in the stomach of the ruminant as the name suggests. Trichostrongylus inhabits the stomach and the small intestine. Nematodirus dwells in the small intestine. It is regarded as a cause of disease in camelids and small ruminants, but is not present in small ruminants in the U.S.
How do these worms survive the winter? On pasture, they survive as eggs or larvae. However, only some species can make it this way. They can also survive as dormant larvae in the host animal (arrested development or hypobiotic), but no disease and no eggs can be detected in the feces! Arrested development is a temporary halt in the parasitic phase of development, usually at the L3 or L4 stage of larval (L) development.
Worms are a greater problem now than 20 years ago. Things that contributed to their success are:
- Climate change - worse in the south, spread north as temperatures have climbed
- Management - high stocking density and small herd/flocks that do not move much
- Drug resistance - in small ruminants we relied only on cheap, powerful drugs to suppress GI worms. In camelids we have done the same, plus we use frequent and extensive prophylactic deworming for meningeal worm disease prevention
- Poor genetics - not selecting breeding stock based on disease resistance!
Drug resistance is a change in the gene frequency of a population that is produced by drug selection whereby more drug is required to exert its effect than was required prior to selection. A drug that used to work no longer does because you have selected for worms that have some means of resisting its effects, by killing off the ones most susceptible to the drug.
These management practices speed up development of resistance:
- Frequent treatments
- Treating all the animals at once
- Under-dosing
- Treating and moving to clean pastures
- Treating when there are not many worms on pasture (drought, end of winter)
- Buying resistant worms through purchasing infect animals
All these decrease the REFUGIA. Refugia is defined as the proportion of the worm population that is not selected by drug treatment. To counteract this, we need worms in untreated animals and eggs and larvae on pasture to provide a pool of sensitive genes to dilute the resistant genes. This is considered the most important factor in preventing the development of drug resistance.
To reduce parasite exposure on pastures, we need to reserve the safest pasture for the most vulnerable animals:
- Lactating females
- Growing animals
- Stressed animals
We can also reduce parasite exposure on pastures by removing the manure, reducing the stocking density, and after grazing, harvesting any regrowth for hay. Also, diversification of our grazing animals is good for parasite control! Alternate or mixed grazing of camelids and small ruminants with horses. Camelids and small ruminants do not share horse parasites and vice versa. Each host is a vacuum cleaner for the parasite larvae of other hosts. It will not work between sheep and goats (cattle?).
Pasture rotation may or may not be helpful in parasite control. Rotation may put animals back right as parasite larvae become infective. Frequency of return is measured in months, not days; leaving pastures open 6 months is ideal for parasite control. (Editor’s note: This would mean an intervening hay harvest to preserve forage. Standing forage would be too mature and/or weathered.)
Some high tannin forages (birds-foot trefoil, sainfoin, sericea lespedeza) seem to have limiting effects on parasites. (More information on sericea lespedeza.)
Selective deworming concentrates dewormer use on animals that need it the most. Uses less dewormer and saves money. It slows development of drug resistance. Untreated worms add to the pool of drug sensitive worms that mate with and dilute out drug resistant worms. Therefore, treat only the most heavily parasitized animals. Worms are not evenly distributed in the host population. Twenty-30% of the animals have most of the worms and deposit 80% of the eggs.
In order to select the animals that need deworming, The FAMACHA© system can be used to the assess the presence of Haemonchus contortus and need for treatment. It estimates the level of anemia, a reduction below normal in the number or volume of red blood cells in the blood. Only the animals with evidence of clinical disease are treated. Use of the FAMACHA selective deworming system in parasite control is for Haemonchus only. This system looks at the lower eyelid of each animal and compares it coloration with those on a chart. A severely anemic animal will have a white lower eyelid and is near death. An eyelid that is pink shows the animal is infested and becoming anemic. Borderline as to whether to treat or not. A light pink eyelid indicates an animal that must be dosed with a wormer.
Small coccidia cause a problem under conditions of overcrowding and reinfestation. It is animal species specific: sheep, goat, camelid, and bovine coccidia will not cross infect. Its infective stage is consumed on pasture and by animals eating feces contaminated hay. It is seen in winter when animals are not on pasture as well as other times of the year. Small coccidia usually are not a significant clinical problem in adults, therefore do not medically treat animals if they are asymptomatic.
Young animals can show signs of diarrhea and poor weight gain. Look for small coccidia oocysts in fecals, but they can take several days to show up after the diarrhea starts. Steve’s rule for diarrhea in a young animal without a fever, is to treat for coccidia even if the fecal is negative. Emphasize cleanliness in the herd/flock to prevent reinfection. Do not treat all of the young animals in the group, but monitor everyone’s feces, growth rate, and body condition. Run periodic fecals to decide who to treat with medication.
E. mac (Eimeria macusaniensis) in camelids was thought of as always being deadly before we started using more accurate techniques to diagnose it. It was then realized that it is very common in animals with no clinical signs of disease. Clinical signs of E. mac infection show up as poor doer adults or young animals. Symptoms are transient or rare diarrhea, poor appetite, weakness, swallowing problems, and rarely even neurological signs. Low blood protein (low albumin) disproportionate to the anemia seen in chronic disease situations in adult camelids and small ruminants. Consider treating poor doer adults of unknown diagnosis with low protein, poor appetite, weakness, swallowing problems for E. mac.
However, most infections are not symptomatic! Their oocysts intermittently shed and not evenly distributed in the feces. It can take weeks (up to 30 to 40 days) to show up on a fecal. You can thus miss them in a single sample from an infected animal so serial sampling is the best strategy. Animals in good body condition with normal feces consistency can have high numbers of oocysts. Stresses, such as shows and transportation, can cause increased shedding. It appears that all farms will see E. mac; similar to small coccidia occurrence. Emphasis must be focused on cleanliness and not overcrowding animals. Overuse of drugs will lead to emergence of resistant parasites!
Tapeworm infestation is usually not an important clinical problem. It can cause diarrhea or loose stools, but not often. Infection occurs sporadically in some localized areas, even on the same farm, and usually in individual animals. Owners see tapeworm segments on manure piles. Wait to see if the problem clears itself. Recheck feces grossly and microscopically to watch for clearing of the parasite.
Trichuris (whipworm) is a completely different type of nematode. Eggs passed in manure. Infective larva forms in egg. Host ingests infective eggs while grazing. Parasites live in the large intestine. The whipworm can cause diarrhea and anemia. Rare cause of disease in sheep and goats but considered significant in camelids and other small ruminants.
Should you treat animals with no clinical signs of disease? No, you should not. Use the results of fecal exams to decide if your parasite management practices are adequate and make the appropriate changes. Do not look first for a different medication!
The adverse clinical signs to look for when deciding to medicate camelids and small ruminants include:
- poor body condition
- failure to grow at a normal rate in young animals
- weight loss
- diarrhea
Deworming medications are poisons. They kill worms and worms are animals. Some medications which have been associated with problems in camelids:
- albazen® has been reported to cause abortion in pregnant camelids
- ivermectin (Ivomec®) and doramectin (Dectomax®) should be considered environmental contaminants as they pass out of treated animals in feces and urine in active form. They can kill beneficial insects such as dung beetles and worms in the soil around manure piles and where fecal runoff occurs. Work done at UMass Amherst where alpacas treated with one subcutan-eous injection of ivermectin had detectable levels of the active drug in the feces for at least two months (Purdy, unpublished data, 2006)!
It is not known whether composting will break down ivermectin and doramectin in feces to make them inactive. It may not be a good idea to put composted camelid and small ruminant manure from animals treated with ivermectin or doramectin on vegetable gardens to prevent ingestion of these compounds by consumers. No regulation against using this manure on organic vegetables!!
If you are using medication to treat parasites:
- Dose animals based on the largest animal in the group (adults, yearlings, young animals, neonates [newborns]).
- Be careful not to overdose neonates as some drugs have narrow safety margins - weigh them.
- Insure adequate dosing, especially orally as some animals may spit out medications.
- In general injectable drug dosing is more accurate.
- “Natural” treatments for parasites include onions, garlic, cranberries, and diatomaceous earth. However, there is no scientific evidence to date that any of these are effective!
- If you use any drug/natural product long enough, resistant worms will develop!
Many areas of the country and farms are faced with intestinal parasites which have developed resistance to deworming medications. We prevent the emergence of drug resistant worms by selective medical treatment, not by blanket treatment of the entire herd/flock. We must: reduce the number of animals treated, and reduce the number of times we treat them to prevent this from occurring. An example of overuse of drugs is the Meningeal Worm Disease prevention programs for camelids. It relied heavily on drug treatments in the eastern US. Animals were being injected frequently with ivermectin or doramectin at monthly intervals depending on the local climate in the winter. Over time, this has resulted in development of drug resistant intestinal nematodes in camelids and small ruminants.
Management; not medicine alone! You most likely cannot eliminate all the
parasites in your animals.
Do you want to? No. Continual use of drugs will make the overall
problem worse!!! Do not overcrowd your animals. In addition to the fecal
contamination, it causes stress on the animals which will suppress their
immune systems and thus make them less able to keep parasites under control.
Bio-security is very important in parasite control. You should always keep transient animals away from the resident herd/flock, in particular away from young animals which all have immature immune systems to start. Outside males and females should never be mixed in with your herd/flock. The stress they undergo when moving may cause them to start shedding parasites which will contaminate your property. You should isolate returning show animals or new arrivals for at least two weeks and run fecals on them regardless of past medical history.
Intestinal parasitism can be controlled with careful attention to good management.