Thysanosoma actinioides, also called the fringed tapeworm, is a helminth parasite that has sheep, goats, other livestock (rarely cattle), and numerous wild ruminants (e.g. elk, deer, etc.) as final hosts.

It is found in North, Central and South America.

Thysanosoma actinioides does not affect dogs, cats, horses, swine or poultry.

Are animals infected with Thysanosoma actinioides contagious for humans?

NO. The reason is that Thysanosoma actinioides is not a human parasite. See the life cycle below.

You can find additional information in this site on the general biology of parasitic worms and/or tapeworms.

Final location of Thysanosoma actinioides

The predilection sites of Thysanosoma actinioides are the bile ducts, the pancreatic ducts, and the small intestine.

Anatomy of Thysanosoma actinioides

Adult Thysanosoma actinioides are 25 to 50 cm long and about 8 mm wide. The head (scolex) is about 1.5 mm long. The segments (proglottids) are about 5 times wider than long and their posterior borders are characteristically fringed.  Each segment has its own reproductive organs of both sexes (i.e. they are hermaphroditic) with two parauterine organs filled with eggs.

The reproductive organs in each segment have a common opening called the genital pore. Each segment has also excretory cells known as flame cells (protonephridia).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 are rather small and have an almost spherical shape (20-25 micrometers), have a thick shell and are embryonated. They are often grouped into packets inside the gravid segments.

Life cycle and biology of Thysanosoma actinioides

The life cycle of Thysanosoma actinioides is not completely understood. It is an indirect life cycle with ruminants (mainly sheep and goats) as final hosts. Oribatid mites (also called "moss mites" and "beetle mites") and barklice (Psocoptera) are suspected to be the main intermediate hosts. 

The adult worms produce eggs that are shed with the feces of the host, mostly inside the 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 develop to adult worms that attach to the wall of the small intestine, the bile ducts or the pancreatic ducts.

Harm caused by Thysanosoma actinioides, symptoms and diagnosis

In case of massive infections the tapeworms can almost block the ducts and disturb the flow of bile or pancreatic juice, which can negatively affect digestion and reduce the weight gains. Otherwise there are usually no specific clinical signs. The major economic significance is condemnation of livers after slaughter. 

As for other related tapeworms (e.g. Avitellina centripunctata, Moniezia spp) diagnosis is based on the presence of gravid segments in the feces and/or the detection of characteristic thick-shelled eggs after fecal examination. Adult tapeworms can be easily identified in the infected organs after slaughter.

Prevention and control of Thysanosoma actinioides

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. albendazole, fenbendazole and praziquantel. These active ingredients are mainly available as drenches. A few ones are also available as slow-release boluses, injectables, feed additives or tablets, but not everywhere.

Excepting slow-release boluses, most 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 Thysanosoma actinioidesor whatever tapeworm.

There are so far no vaccines against Thysanosoma actinioides. To learn more about vaccines against parasites of livestock and pets click here.

Biological control of Thysanosoma actinioides (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 Thysanosoma actinioides to anthelmintics

There are only very few reports /e,g, in Bolivia) on resistance of Thysanosoma tapeworms to benzimidazoles (e.g. fenbendazole) but it is certainly not yet a widespread problem.

This means that if an anthelmintic fails to achieve the expected efficacy against this parasite, chance is very high that it is not due to resistance, but either the product was used incorrectly, or it was unsuited for the control of this parasite. Incorrect use is the most frequent reason for failure of antiparasitic drugs.