Current thoughts on camelid gastrointestinal parasites (Proceedings)

Gastrointestinal parasites of camelids

There are several classes of gastrointestinal parasites which affect camelids to varying degrees. The intestinal nematodes affecting North American camelids include Trichostrongyle spp., Nematodirus spp., Haemonchus spp., Ostertagia spp., Trichuris spp. and Capillaria spp. The cestode, Monezia spp., may also be of some clinical significance. Protozoal concerns include Eimeria spp., Cryposporidium parvum and Giardia 1 spp. Trematodes have also been shown to cause clinical disease in the biliary system of camelids, including Fasciola spp. and Dicrocoelium dendriticum. This document will focus on the control of gastrointestinal nematodes and coccidia of camelids.

Disease syndromes

Parasite infestations in camelid herds frequently cause insidious disease and go unrecognized until an individual animal succumbs to the disease. For this reason, cases of severe parasitism in an individual should lead to a herd investigation of prevalence and management techniques.

Clinical signs of parasitism may include weight loss, lethargy, ill-thrift, pale mucous membranes, edema, poor lactation and poor growth. Late gestation and lactating females may experience pregnancy toxemia and hepatic lipidosis secondary to a negative energy balance compounded by parasitism. Hypoproteinemia and anemia are hallmarks of Haemonchus infestation, but may be present with other parasites. Additionally, E. macusaniensis has been associated with colic, enterotoxemia5 and circulatory shock6 in alpacas and coccidia may be involved in the pathogenesis of intussusception. E. macusaniensis has been reported to have a 50% mortality rate in treated animals, with severe disease occurring during the prepatent period.

Because of the wide array of clinical syndromes associated with gastrointestinal parasitism, all ill camelids and death losses should have a parasitology examination performed.

Diagnostic testing

Proper selection of diagnostic tests must occur to properly monitor parasite burdens in herds. Many herds elect to simply use dewormers at regular intervals or deworm thin animals without performing diagnostics. The target must be known when treating or managing parasites. While some dewormers are broad-spectrum, none are full-spectrum. The author has seen "pure" clinical infestations of a single nematode type because of the repeated use a single dewormer without knowledge of the target.

Regular fecal sampling of 10 or 10% of each production group (ie. 3-6 month old cria, weanlings, adult females, adult males, etc.) should occur. All new additions to a farm (this includes those returning from breeding, even for a short time) should be tested while in quarantine. Additionally, any immunosuppressed and periparturient animals should be tested to monitor egg counts.

Both quantitative and qualitative testing should be performed on all camelid fecals samples. Qualitiative testing is performed at Kansas State University using sugar flotation, with double centrifugation. Following this, quantitative testing should be done. The Modified Stoll's egg-counting procedure is sensitive to 5-10 eggs per gram (EPG), which will detect Trichuris, Capillaria and Nematodirus, which shed a small number of eggs. The McMaster's Technique is only sensitive to 25-50 EPG, which may not catch eggs from low egg-shedding parasites. The KSU lab uses the Modified Wisconsin Sugar flotation method for quantification, which counts all the eggs in 3g of feces. It is recommended that at least 5g of feces be provided for each sample submitted to the laboratory.

A comparison study was performed using direct smear, Modified McMaster's with sucrose or saline (flotation for 15 and 60 minutes) and Centrifugation-sucrose flotation procedures (overnight soak, with 10 and 60 minute flotation) for the detection of parasites in llamas and alpacas Centrifugation-flotation found more of all parasites except the small coccidia, but small coccidia could be found if flotation occurred for 60 minutes. The sucrose solution had improved ability to demonstrate Trichuris, E. macusaniensis and strongyles, while the saline solution more often demonstrated Nematodirus and small coccidia.

To monitor efficacy of drugs, the Fecal Egg Count Reduction Test (FECRT) should be performed. In this testing, a quantitative test appropriate for the farm is performed and, if needed, anthelmintics are administered. Following this, the same quantitative test is repeated on the same animals in 14 days to determine EPG reduction. Although not specifically described for camelids, a reduction in EPG count of >95% indicates drug efficacy. If a reduction of >90% is not seen, causes of treatment failure should be investigated [see section below: "Anthelmintic Resistance"]

The use of the FAMACHA® system, as in sheep and goats, has been preliminarily evaluated in llamas and alpacas. In this system, animals are scored based on ocular mucous membrane color for anemia, with 1 indicating no anemia and 5 indicating severe anemia. The goal of this system is to identify animals clinically affected with Haemonchus so that only affected animals are treated, therefore minimizing anthelmintic exposure in the herd. FAMACHA® scoring was used to evaluate 921 alpacas and llamas for anemia. Results of the study (clinical impression) indicate that llamas and alpacas scoring 1 or 2 were not anemic and animals scoring 5 were significantly anemic. The study also revealed that scoring camelids was not as simple as in sheep and goats, due to difficulty in handling the head and some differences in membrane color within animals. Recall that FAMACHA® scoring monitors only for Haemonchus and does not provide any information about the remaining nematodes and parasites which can cause significant disease.

Whatever diagnostic test is used, fecal pellets must be broken up prior to flotation, with refrigeration overnight enhancing breakdown. Diagnostic fecals which are to be used for therapeutic decision- making should only be performed by those trained and experienced with camelid fecals and who have the expertise and licensure to make decisions about appropriate extra-label drug usage.

Anthelminthic resistance

Anthelminthic resistance receives a lot of discussion and is a concern in all veterinary species. It is a randomly-occurring event, which may be accelerated by drug misuse and animal mismanagement.

Anthelmintic efficacy was studied on three camelid farms in Georgia, using the FECRT (modified McMaster technique - salt). Animals with EPG counts >100 were included in the study and resistance was found to ivermectin in both llamas and alpacas, with resistance to fenbendazole and moxidectin demonstrated on llama farms. All three farms in the study previously practiced regular, herd-wide deworming with dosing intervals ranging from every 5-6 weeks to quarterly.

Pharmacologic prevention of meningeal worm, which typically involves the administration of monthly injectable avermectin products to susceptible animals during the transmission season, may accelerate the development of genetic resistance in gastrointestinal nematodes. For this reason, camelid farms in low-risk regions of the country should avoid pharmacologic prevention measures and farms in high-risk regions of the country should consider other preventative measures to minimize herd exposure.

It is important to remember that, although resistance is present to some extent in all populations, a dewormer that has apparent poor efficacy (treatment failure) does not necessarily indicate resistance. Treatment failure may occur as a result of reinfestation (high stocking density, high environmental contamination), underdosing (inaccurate weight estimates, spit out), diminished drug activity (prolonged storage or storage in extreme conditions), inconsistent or qualitative diagnostic testing and selection of improper anthelmintic for the targeted parasite.

Causes of actual resistance may include underdosing, frequent deworming, rotation of dewormers, and use of pour-on deworming products as either a dewormer or external parasiticide.

Non-pharmacologic control strategies

The primary focus of every farm should be to maintain an environment that minimizes herd exposure and susceptibility to parasites. This is done through stocking, pasture and dung pile management, herd health and nutrition and careful monitoring of parasite levels. The ability of parasite ova to become hypobiotic and re-emerge at times of environemental favorability and the prolonged infectivity of the oocysts of E. macusaniensis, which have been shown to maintain infectivity after storage of 41-84 months) makes reducing environmental exposure of utmost importance.

Refugia refers to the parasite population which has not been exposed to dewormers, which include susceptible populations on pasture and in untreated animals. Progeny of surviving worms which have been exposed to dewormers possess some resistance, by definition. These progeny will be put out into the environment and will be infective to other animals. The goal is to have refugia (believed to be largely drug-susceptible) intermixed, and hopefully outnumbering, these resistant progeny to dilute the population. A concept which is often difficult to convey is that we actually want animals to have some susceptible parasites present. The goal is to have a breeding population of worms to dilute any genetic development of resistance.

A "positive" fecal is to be expected in any grazing animal and the practice of deworming to a negative fecal is detrimental in many ways. Practices which harm refugia and therefore increase parasite problems include treating and moving animals regularly, treating during times of poor parasite survival, rotation of anthelminthics, treating all animals, treating on a regular, frequent schedule and underdosing of dewormers. When you treat and move, the eggs dropped on the new, clean pasture will be those of resistant worms. To encourage the presence of healthy refugia, animals should be treated on an individualized basis and only when necessary.

Nutrition likely plays a significant role in the host's ability to overcome parasitism. In sheep, protein and trace mineral status have been shown to have an effect on performance in animals in the face of parasitism. Additionally, cobalt deficiency has been shown to reduce immunity against nematodes and with supplementation of other minerals promoting immune function.

Recommendations for control of gastrointestinal parasites in camelids include:

     • Full-time stocking density should be limited to 6-8 animals per acre of usable land.

     • Rotational grazing is advisable, with sufficient fencing to allow each production group to move.

     • Dung piles should be completely removed at least weekly, with some farms requiring daily removal of dung piles. It is important to note the location of dung piles and alter the layout of a drylot or pasture accordingly. Where dung piles are placed in a shelter or near a feeder, attempts should be made to have more frequent removal or movement of the feeder. Having the dung pile near a shelter prevents heat and drying of the pile, which is useful to significantly impair parasite survival.

     • Feed from a raised feeder, rather than on the ground. It is common for small and meek animals to be limited to eating off the ground from feed dropped out of the feeder. This places them at the level of the parasite load, particularly if a dung pile is nearby. Feeding behavior should be monitored and additional bunk space made or separations occur to allow for raised eating of all animals.

     • Animals should receive appropriate nutrition for each stage of production. Palatable trace minerals should be supplied to all animals at all times and consumption monitored.

     • Bedding should be changed out to allow drying and dirt surfaces under shelter should be disturbed or uncovered to allow thorough drying.

     • Fecal egg counts should be performed on 10 or 10% of each production group on a regular basis, with a focus placed on young and juvenile animals. These must be done by laboratories with a consistent record of quality control regarding camelid fecal examination.

     • Deworming at regular intervals should be strongly discouraged. In areas where meningeal worm is a high risk, the risks and benefits of pharmacologic prevention should be weighed, with non-pharmacologic means of prevention considered.

     • Dewormers, when found to be necessary by fecal egg count testing, should be utilized on a farm until they are found to no longer have efficacy. Dewormers should not be routinely rotated.

     • All animals coming onto the farm (including those who belong on the farm, but have been away) should have fecal egg counts performed at the start and at the end of quarantine.

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