Mecistocirrus digitatus is a parasitic roundworms belonging to the family calledTrichostrongylidae, which includes many other parasitic worms of livestock. Mecistocirrus digitatus is the only species of its genus. It affects cattle, sheep, goats, other ruminants and pigs.
It is found mainly in tropical and subtropical regions of Central and South America, Africa, Asia and sporadically in Europe as well. Incidence varies locally and seasonally. Where it occurs it is mostly found mixed with other gastrointestinal roundworms (Haemonchus, Cooperia, Ostertagia, Oesophagostomum, etc). In such mixed infections it can make up to 30% of the gastrointestinal worms found in infected animals.
Neither dogs nor cats are affected by this species. Human infections are possible but very seldom.
Is livestock infected with Mecistocirrus digitatus contagious for humans?
- Normally not. Human infections are very exceptional. Direct contact with livestock or their fresh feces is not contagious for humans because the eggs shed with the feces have to mature in the environment to become infective. This takes about 2 weeks. For more details about the life cycle of these worms see below.
Final location of Mecistocirrus digitatus
Predilection site of adult Mecistocirrus digitatus is the stomach.
Anatomy of Mecistocirrus digitatus
Adult Mecistocirrus digitatus are similar to those of the genus Haemonchus. They are up to 4 cm long, whereby females are larger than males.
As other roundworms the body of these worms is covered with a cuticle, which is flexible but rather tough. The cuticle of Mecistocirrus digitatus shows about 30 longitudinal ridges and a fine transverse striation. The worms have no external signs of segmentation. They have a tubular digestive system with two openings. They also have a nervous system but no excretory organs and no circulatory system, i.e. neither a heart nor blood vessels.
The female ovaries are rather large. Characteristic for this species is that the ovaries are coiled around and along the gut. Males have two very long and slender spicules for attaching to the female during copulation.
The eggs are ovoid, about 70x110 micrometers, with a thin shell, and similar to other eggs of the same family.
Mecistocirrus digitatus has a direct life cycle, i.e. there are no intermediate hosts involved. Adult females lay eggs in the stomach of the host that are shed with the feces. Once in the environment the eggs release the L1-larvae that complete development to infective L3-larvae in about 2 weeks, depending on temperature and humidity. Such infective larvae can remain infective in the environment for months.
Livestock become infected after ingesting such larvae while grazing. Ingested larvae complete development to adults inside the stomach (abomasum in ruminants) in about 6 to 10 weeks. Some larvae penetrate into the gastric pits (i.e. the entrance to the gastric glands) or into the lining of the abomasum (in ruminants), but most larvae remain in the stomach lumen. Adults attach to the stomach lining and feed on blood that flows out of the small injuries they cause with their teeth.
The prepatent period (time between infection and first eggs shed) is 7 to 12 weeks.
Harm caused by Mecistocirrus digitatus, symptoms and diagnosis
Mecistocirrus digitatus can be seriously harmful for livestock in endemic regions, especially for young stock. It harms the stomach lining to get access to blood. Clinic signs are similar to those of Haemonchus species. Acute symptoms include anemia, sometimes hemorrhagic, dark feces and abdominal, thoracic and submandibular edema (i.e. swelling of the jaw, so-called "bottle jaw").
Sudden death after exercise can happen. Chronic infections often show iron-deficiency anemia, intermittent constipation, loss of appetite, weight loss, and progressive wasting.
Livestock exposed to these worms often develop natural resistance progressively. Such resistant animals do not become sick if infected, but continue shedding eggs that infect their environment.
Diagnosis is comfirmed through detection of characteristic eggs in the feces.
Prevention and control of Mecistocirrus digitatus
Systematic and thorough removal of all manure and keeping the facilities dry reduces the risk of infection. Since development of eggs to infective L3-larvae takes at least 5 days, removing all manure in shorter intervals can break the life cycle and reduce the infectivity of the environment. Other preventative measures are the same as for all gastrointestinal worms and are explained in a specific article in this site (click here).
Numerous anthelmintics are effective against adult worms, e.g. several benzimidazoles (albendazole, febantel, fenbendazole, flubendazole, mebendazole, oxfendazole, etc.), levamisole, as well as several macrocyclic lactones (e.g. abamectin, doramectin, eprinomectin, ivermectin, moxidectin). However, in some countries many wormers may not include Mecistocirrus digitatus as an approved indication.
Depending on the country most of these anthelmintics are available for oral administration as drenches, feed additives and/or tablets. Levamisole and most macrocyclic lactones are usually also available as injectables. A few active ingredients are also available for livestock as pour-ons and slow-release boluses.
Excepting slow-release boluses, most wormers containing benzimidazoles (e.g. albendazole, febantel, fenbendazole, flubendazole, mebendazole, oxfendazole, etc.), levamisole, tetrahydropyrimidines (e.g. morantel , pyrantel), piperazine derivatives and other classis anthelmintics kill the worms shortly after treatment and are quickly 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. An exception to this are macrocyclic lactones (e.g. abamectin, doramectin, eprinomectin, ivermectin, moxidectin) and closantel, that offer several weeks protection against re-infestation, depending on the delivery form and the specific parasite.
There are so far no true vaccines against Mecistocirrus digitatus. To learn more about vaccines against parasites of livestock and pets click here.
Biological control of Mecistocirrus digitatus (i.e. using its natural enemies) is so far not feasible. Learn more about biological control of worms.
You may be interested in an article in this site on medicinal plants against external and internal parasites.
Resistance of Mecistocirrus digitatus to anthelmintics
Little has been published regarding confirmed resistance of Mecistocirrus digitatus against most used anthelmintics (benzimidazoles, ivermectin, levamisole, etc). However, since many gastrointestinal roundworm species have developed such resistance in many countries, it must be feared that Mecistocirrus digitatus is not an exception.
This means that if an anthelmintic Mecistocirrus digitatus, there is a certain risk that it is due to resistance to anthelmintics, particularly in sheep, goats and cattle. Nevertheless, it is known that most cases of product failure are due to incorrect use of a product or to the use of an unsuited product, not to resistance.
Ask your veterinary doctor! If available, follow more specific national or regional recommendations for Mecistocirrus digitatus control.