Tapeworms: problem or not?
Tapeworms often cause more concern among sheep and goat producers than stomach worms (nematodes), because producers can see the obviously expelled worms, whereas they cannot see stomach worms, only their symptoms or eggs (in the feces).
Tapeworms are flat, ribbon-shaped worms that live inside the intestines of humans or animals that have a spine. They are long, segmented worms of the class Cestoda, which comprise one of three classes of parasitic worms. The other classes are Nematoda (roundworms) and Trematoda (flukes). Cestodes lack an intestinal tract, but are able to absorb nutrients through their skin.
Adult tapeworms have hooks, spiny structures, or suckers on their head, which allow them to attach to the wall of the intestine. The rest of the tapeworm is made up of a chain of flat segments. The adult tapeworm consists of a head (scolex), where the worms attaches itself to the mucosa of the intestine; a neck; and a segmented body that contains both male gonads and female gonads (proglottids). Mature tapeworms shed segments, which are expelled with the feces. These segments are packed with eggs.
Life Cycle (2,3)
Cestodes (tapeworms) require an intermediate host to complete their life cycle. Different tapeworms require different intermediate hosts. All of the important species affecting sheep, goats, and cattle require pasture mites. These mites ingest the eggs while feeding and the larval stages of the worm develop inside the mites.
Oribatid mites live in the top layer of soil. Sometimes they can be found in plant material. These mites live in huge numbers. Hundreds of thousands can live in one square meter of soil. To see one well, you would need a microscope. Sheep and goats become infected when they ingest the mites containing tapeworm larvae. Once inside the animal, it takes 6 to 7 weeks for the larvae to develop into adult tapeworms.
Moniezia expansa is the tapeworm that commonly affects sheep and goats. Moniezia benedeni, more common in cattle, can also be found in sheep and goats. Sheep and goats serve as intermediate hosts for several other species of tapeworms.
Tapeworm segments can be seen in the feces of sheep and goats. They have a white, grain-like appearance. Adult worms, often up to a meter or more in length, can be expelled and passed in the environment. Tapeworm eggs can be seen in sheep and goat feces, using the standard worm count procedure. Eggs are triangular in shape.
Diagnosis
Definitive diagnosis in the live animal is difficult and sometimes a post-mortem is necessary to confirm an accurate diagnosis. Tapeworm infection is more typically diagnosed when the moving segments are seen crawling around the anus or in a bowel movement. While tapeworm eggs can be seen in fecal flotation under a microscope, fecal analyis does not offer a definitive diagnosis.
The symptoms of clinical tapeworm infection are similar to the symptoms of other roundworm infections: diarrhea, emaciation, pot belly, and weight loss. In sufficient numbers, tapeworms can obstruct the bowel and cause death. Sheep seem to develop an immunity to tapeworms relatively early in life (3-4 months of age).
Treatment and control
Four drugs are used to treat tapeworm infections in animals: praziquantel, albendazole (Valbazen®), oxyfendazole (Synathic®), and fenbendazole (SafeGuard®, Panacur®). In the United States, praziquantel is marketed for dogs and cats under the tradenames Droncit® and Drontal®. Praziquantel is an ingredient in several horse dewormers: Zimecterin® Gold Paste, Equimax™ Paste, and Quest® Plus Gel. Many anthelmintics marketed in other countries (for sheep and goats ) have a praziquantel component. There are no anthelmintics which contain praziquantel that are currently labeled for sheep and goats in the U.S.
Praziquantel is effective against both the adult and immature stages of tapeworms whereas the benzimidazole anthelmintics only kill the head and segments. Albendazole is considered to be the most effective of the benzimidazole drugs. While it usually less effective than praziquantel, it is usually sufficient for controlling tapeworm infections. Fenbendazole is not labeled for the control of tapeworms (in goats), but will aid in their removal (heads and segments), if the dose is doubled. Oxfendazole is not label for use in either sheep or goats in the U.S.
There are several old remedies with purported activity against adult tapeworms. These include pumpkinseeds, powdered areca (fruits of betel palm, Areca catechu), kousso (flowers of an Abyssinian tree, Hagenia abyssinica), turpentine (oily mixture of exsudates from coniferous trees, especially longleaf pine), pomegranate root bark (tropical Asian and African tree, Punica granatum), and male fern (Dryopteris filix-mas).
For a long time, lead arsenate (often mixed with phenothiazine) was used to treat tapeworm infection in lambs. It's safety margin is low; thus, it is no longer used.
Reviews of research show that tapeworms do not cause any ill effects on sheep or lambs despite their rather troublesome appearance. If sheep or lambs are looking poorly and tape segments are in the dung, you should probably look for causes other than tapeworms. The true cause of ill thrift is probably nutritional or other non-visible worms such as Haemonchus contortus (barber pole worm).
Review of the scientific literature
The pathogenicity of tapeworms is continuously debated. Due to the lack of research evidence to the contrary, most scientists and small ruminant veterinarians believe tapeworms to be non-pathogenic. Other experts consider tapeworms to be a threat to young animals, especially up to the age of weaning.
Researchers often note the difficulty in conducting trials with natural infections, which vary greatly in age and magnitude. Few studies with goats have been conducted and none could be found (by this author) on the Internet. As with other gastro-intestinal parasites, goats may be more susceptible to the effects of tapeworm infection than sheep.
In New Zealand (4)
In the December 2007 issue of Turning the Worm, the author reviewed tapeworm research previously done in New Zealand. He wrote, "Over the years, there have been many investigations in New Zealand, all but one of which have failed to show any relationship between tapeworms and production loss." Treatments with niclosamide showed no benefits in terms of weight gain, fecal consistency or dagginess between treated and untreated lambs.
In the one study that showed a relationship, 93 naturally-infected lambs were slaughtered 10-12 days after treatment with praziquante or albendazolel. Praziquantel treatements were 99-100% effective at removing Moniezia while albendazole treatments were 19-75% effective at removing Moniezia when compared to untreated controls.
In a productivity trial, 300 undrenched Romney lambs were assigned to one of three treatment groups: untreated (control), levamisole, and praziquantel + levamisole. The lambs were grazed together throughout the trial. The levamisole-treated lambs gained significantly more weight than the untreated controls, and the praziquantel + levamisole-treated lambs gained significantly more weight than the levamisole-treated lambs. The level of infestation of the trial lambs with Moniezia was not reported.
The effects of albendazole and praziquantel against tapeworms were compared in two productivity trials and a slaughter trial in the Wairarapa region of New Zealand. The trials involved over 400 lambs on two farms. Fecal egg counts showed that more than 50% of the lambs were shedding tapeworm eggs, indicating a high rate of infection when the study was initiated.
The control group of lambs received moxidectin only. A second group received levamisole + praziquantel, as well as moxidectin. The third group received albendazole + levamisole, as well as moxidectin. Moxidectin was given to eliminate possible differences between levamisole and albendazole in nematocidal activity.
At days 11 (farm A) and 7 (farm B), no tapeworm eggs were seen in the samples collected from the praziquantel-treated lambs, but were still present in lambs in the other two groups. At days 63 (farm A) and 59 (farm B), no tapeworm eggs were seen in any of the fecal samples. There was no significant difference in weight gain over the duration of the experiment (approx. 80 days) between the controls and either treatment group.
The slaughter trial included four groups of lambs: untreated controls, albendazole-treated, albendazole + levamisole, and levamisole + praziquantel. Lambs were slaughtered 12 days post-treatment and the small intestines were examined for tapeworms. All lambs in the control group had tapeworms. There was a 50-60% reduction in tapeworm head and segments in lambs treated with albendazole or praziquantel. Praziquantel was not fully effective, suggesting the possiblity of drug resistance.
A German study (6)
In a more recent study reported in the Wool & Wattles newsletter of the American Association of Small Ruminant Practioners, German researchers used two flocks of sheep and several breeds of sheep to determine the effect of treatment (with praziquantel) on tapeworms. The results showed no evidence of the pathogenicity of tapeworms in lambs. Nor did they demonstrate a beneficial effect of treatment.
Lambs were randomly assigned to a treatment (n=117) or control (n=117) group. Individual fecal flotations were performed (with zinc chloride and sodium chloride). The treated animals received a commercial 2.5% solution of praziquantel (at 3.75 mg/kg) orally, repeated every six weeks for up to four treatments. All lambs received moxidectin on the same schedule (at the labeled dosage) to remove the possible effects of nematodes on lamb health.
At the beginning of the trial in June-July, 28 to 45 percent of the lambs tested positive for tapeworms eggs. The percentage dropped off markedly in both the treated and untreated (control) lambs, such that only 0 to 7% of treated animals and 0 to 9% of untreated animals had detectable eggs at the last sampling before slaughter (up to 140 days after the beginning of the trial).
There were no significant differences in body weight between the two groups. In fact, the animals that remained infected with tapeworms were often heavier than the average of the uninfected lambs. Five of 45 of the treated lambs that were necropsied (up to 29 days after the final treatment) had juvenile tapeworms in their intestines, while 29 of the 67 control lambs contained juvenile tapeworms.
Other tapeworm infections (1)
Sheep and goats also serve as the intermediate host for several other species of tapeworms. Echinoccus granulosus causes hydatid disease in livestock and humans. Taenia ovis causes "sheep measles" (ovine cysticercosis). Both have life cycles involving dogs as definitive hosts and sheep and goats as intermediate hosts.
The adult worms cause few symptoms in the dog, but the cystic stages can cause considerable damage to the intermediate host. Hydatid disease can be life threatening to humans and is the result of accidental ingestion of hydatid eggs from dogs. Though not considered a human health risk, cysts caused by T. ovis can get in the meat and organis and cause a carcasses to be condemned.
The best way to prevent these problems is to keep dogs (domestic and wild) from eating carrion or other raw meat. Scientists have developed an effective vaccine for sheep against. T. ovis and E. granulosus; however the vaccine is currently not available in the U.S.
References and further reading
(1) Sheep measles: another profit killer. Prime Fact 55. January 2008. DPI. New South Wales, Australia.
(2) Life cycle of Moniezia expansa. Biology of the Goat.
(3) Tapeworms of sheep. Australian Wool Innovation Limited.
(4) Turning the worm. Issue 22, December 2007. DPI. New South Wales, Australia.
(5) What about tapeworms in sheep? WormBoss News. August 2012.
(6) Wool and Wattles. October-December 2007. American Association of Small Ruminant Practitioners.
(7) Disgusting tapeworms - ACSRPC
This article was written in 2008 by Susan Schoenian.