Stilesia hepatica, also called the liver tapeworm, is a helminth parasite that has sheep, goats, other livestock and numerous wild ruminants (e.g. elk, deer, moose, etc.) as final hosts.
It is found North and South America in Asia and in tropical and southern Africa.
Stilesia hepatica does not affect dogs, cats, horses, swine or poultry.
Are animals infected with Stilesia hepatica contagious for humans?
NO. The reason is that Stilesia hepatica is not a human parasite. See the life cycle below.
Final location of Stilesia hepatica
The predilection sites of adult Stilesia hepatica are the bile ducts and sometimes the small intestine.
Anatomy of Stilesia hepatica
Adult tapeworms are 25 to 50 cm long and about 3 mm wide. The head (scolex) has four prominent suckers. The segments (proglottids) are short. Each segment has its own reproductive organs of both sexes (i.e. they are hermaphroditic) with two parauterine organs filled with eggs. Each segment has also excretory cells known as flame cells (protonephridia).
The reproductive organs in each segment have a common opening called the genital pore. In young segments all these organs are still rudimentary. They develop progressively, which increases the size of the segment as it is pushed towards the tail. Mature gravid segments are full of eggs (several thousands) and detach from the strobila (i.e. the chain of segments) to be shed outside the host with its feces.
Otherwise, as other tapeworms, they have neither a digestive tube, nor a circulatory or respiratory systems. They don't need them because each segment absorbs what it needs directly through its tegument. Individual gravid segments in the feces are visible by the naked eye.
The eggs have an oval shape and are rather small (16x25 micrometers).
The adult worms produce eggs that are shed with the feces of the host, mostly in the form of gravid segments. Depending on the species and the region they can survive for months in the environment and some may survive cold winters, but they are very sensitive to dessication.
The intermediate hosts ingest the eggs, which develop to infective cysticercoids in their body cavity. The final host becomes infected after ingesting such contaminated intermediate hosts while grazing. After digestion the released cysticercoids attach to the gut's wall and develop to adult tapeworms within a several weeks, depending on the worm species and the final host.
Harm caused by Stilesia hepatica, symptoms and diagnosis
Infections with Stilesia hepatica are not pathogenic even in case of massive infections, with are quite common in endemic regions. Clinical signs are very seldom. The only major harm is condemnation of the livers at slaughter, more for esthetic than for safety reasons, since these worms are not contagious for humans.
Diagnosis is usually made only after slaughter. Fecal examination shows gravid segments (proglottids, may look lice rice grains) in the host's excrements.
Prevention and control of Stilesia hepatica
It is not possible to eliminate the mites or other intermediate hosts in the pastures. The use of insecticides for this purpose is not advisable, because it is more expensive than the potential economic loss due to the infections, and because it detrimental effect on the environment: it would kill not only the intermediate hosts, but numerous beneficial insects as well.
A few anthelmintics are effective against tapeworms, e.g. fenbendazole and praziquantel, but have to be administered at two to four times the normal therapeutic dose, which is economically unadvisable because treatment does not improve productivity.
Excepting slow-release boluses, the vast majority of wormers kill the worms shortly after treatment and are metabolized and/or excreted within a few hours or days. This means that they have a short residual effect, or no residual effect at all. As a consequence treated animals are cured from worms but do not remain protected against new infections. To ensure that they remain worm-free the animals have to be dewormed periodically, depending on the local epidemiological, ecological and climatic conditions.
Other classic livestock anthelmintics such as macrocyclic lactones (e.g. ivermectin, doramectin, moxidectin, etc.), levamisole, tetrahydropyrimidines (e.g. pyrantel, morantel) and piperazine derivatives are not effective at all against Stilesia or whatever tapeworm.
There are so far no vaccines against Stilesia hepatica. To learn more about vaccines against parasites of livestock and pets click here.
Biological control of Stilesia hepatica (i.e. using its natural enemies) is so far not feasible.
You may be interested in an article in this site on medicinal plants against external and internal parasites.
Resistance of Stilesia hepatica to anthelmintics
So far there are no reports on resistance of Stilesia hepatica tapeworms toanthelmintics.
This means that if an anthelmintic fails to achieve the expected efficacy, chance is very high that either the product was unsuited for the control of Stilesia hepatica tapeworms, or it was used incorrectly.
Ask your veterinary doctor! If available, follow more specific national or regional recommendations for Stilesia hepatica control.