Toxocara vitulorum is a species of parasitic roundworms that infects cattle, buffaloes, bisons and other bovids. It is also called Neoascaris vitulorum.
It is found worldwide, including Europe, but is more abundant in regions with humid tropical or subtropical climate in Africa, America and Asia. Up to 100% of the calves can be infected in endemic regions with poor control measures. Water buffaloes seem to be particularly susceptible to Toxocara vitulorum infections.
These worms do not affect sheep, goats, pigs, horses, dogs or cats.
The disease caused by Toxocara vitulorum is called toxocariasis or toxocariosis.
Is livestock infected with Toxocara vitulorum contagious for humans?
- NO, but: There is still no evidence that Toxocara vitulorum can infect humans. However, eggs ingested by paratenic hosts can migrate to various tissues, and they could do so in humans as well. Human toxocariasis due to Toxocara canis or Toxocara cati is usually diagnosed through ELISA tests that are mostly incapable of distinguishing between these species and Toxocara vitulorum.
Final location of Toxocara vitulorum
Predilection site of adult Toxocara vitulorum is the small intestine. Migrating larvae can be found in numerous organs: lungs, trachea, bronchi, liver, kidneys, mammary glands, etc.
Anatomy of Toxocara vitulorum
Adult Toxocara vitulorum are the largest worms that infect cattle. They can be up to 40 cm long and 7 mm thick, whereby females are larger than males. They have a whitish color and a translucent aspect, and look very much like cooked spaghetti. As in other roundworms, the body of these worms is covered with a cuticle, which is flexible but rather tough. It forms two characteristic wing-like projections (alae) in the anterior end. The worms have a tubular digestive system with two openings, the mouth and the anus. 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 large and the uteri end in an opening called the vulva. Males have a copulatory bursa with two short spicules for attaching to the female during copulation.
The eggs are almost spherical, about 70x80 micrometers., have a thick and pitted membrane and contain a single cell.
Toxocara vitulorum has a direct life cycle, i.e. there are no intermediate hosts involved. Adult females lay eggs in the small intestine of the host that are shed with the feces. These species is one of the most prolific worms: an infected calf can shed up to 8 million eggs daily! Once in the environment L2-larvae develop inside the eggs in about 7 to 15 days at 27°C to 30°C, the ideal temperature. Development stops below 12°C but can resume when temperature rises again. These eggs are infective and contaminate the pastures. They can survive for months and possibly years, but are sensitive to sunlight.
Adult livestock becomes infected after ingesting embryonated eggs. Larvae emerge from the eggs in the gut, penetrate the gut's wall and migrate through the bloodstream either to the liver, lungs, trachea, mouth, esophagus and back to the small intestine where they complete development to adult worms and begin producing eggs; or they migrate to other tissues, including the mammary glands and the placenta of pregnant cows from where they can be transmitted to the calves or to unborn embryos, respectively. Larvae can survive on tissues for up to 5 months. Larvae that reach the mammary glands remain dormant until about 3 weeks before parturition when they are re-activated and passed to the sucklings with the milk during the first 3 weeks after parturition (lactogenic transmission). Transmission through the milk seems to be the most frequent infection way in calves.
In infected calves, larvae that reach the intestine do not migrate but develop directly to adult worms in about three weeks after birth or after being ingested with the milk. Maximum egg output occurs in calves up to 3 months old, and ends quickly after.
The prepatent period (time between infection and first eggs shed) is 3 to 4 weeks in calves. In adult cows it is longer, depends on the migration and dormancy periods. However, it seems that most larvae do not complete development and lay eggs in adult cows but are perinatally transmitted to the offspring.
Harm caused by Toxocara vitulorum, symptoms and diagnosis
Toxocara vitulorum is usually not pathogenic for adult cattle. But it can be very harmful to calves in tropical and subtropical regions with high mortality rates if left untreated.
Migrating larvae can seriously damage numerous organs in adult cattle, particularly the lungs, where they can cause infections with secondary bacteria and subsequent pneumonia. In calves, the adult worms in the small intestine compete for nutrients with the host, and can cause diarrhea (often putrid), colic, enteritis, loss of appetite and weight. Due to the large size of the worms massive infections can obstruct the gut and even perforate it. Fatalities are not infrequent. Occasionally worms may also migrate through the bile duct and obstruct it causing cholangitis.
Diagnosis is based on detection of typical eggs in the feces. However, pregnant cows without any detectable eggs in their feces may be infected with dormant larvae in the tissues that will be passed to their offspring. In some countries immunoassay (e.g. ELISA) are available for serological diagnosis. A typical sign of Toxocara vitulorum infections in calves is a characteristic butyric acid or acetone odor on breath and/or urine that may even stick to meat and cause rejection at slaughter.
Prevention and control of Toxocara vitulorum infections
Since calves are more susceptible against these worms and most infections are acquired perinatally from infected dams, it is essential to try to prevent the infection of pregnant cows. Since most eggs are shed by young calves pastures occupied by these calves will often be highly contaminated. If cows cannot be kept off these contaminated pastures, they have to be treated with appropriate anthelmintics.
In properties with a history of Toxocara vitulorum infections thorough hygienic measures (manure removal!) and disinfection of the calf boxes are highly recommended.
Toxocara vitulorum being cattle specific, alternate grazing with sheep and/or horses may be considered. The longer the absence of cattle, the higher will be the reduction of the Toxocara vitulorum population in the pastures. However, this may not be advisable if the property has other gastrointestinal roundworms that are simultaneously parasitic of cattle and sheep or horses.
Other preventative measures for gastrointestinal roundworms are explained in a specific article in this site (click here).
So far no true vaccine is available against Toxocara vitulorum. To learn more about vaccines against parasites of livestock and pets click here.
Biological control of Toxocara vitulorum (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.
Numerous broad spectrum anthelmintics are effective against adult worms and larvae in the gut, e.g. several benzimidazoles (albendazole, febantel, fenbendazole, oxfendazole, etc.), levamisole, as well as several macrocyclic lactones (e.g. abamectin, doramectin, eprinomectin, ivermectin, moxidectin). But not all of them are effective against migrating larvae and/or arrested larvae in the tissues. Read the product label carefully to find it out.
A few other narrow-spectrum anthelmintics such as tetrahydropyrimidines (e.g. morantel, pyrantel) and piperazine derivatives are effective against adult worms but may not control larvae and other roundworm species that often infect livestock simultaneously with Toxocara vitulorum worms.
Numerous commercial products contain mixtures of two or even more active ingredients of different chemical classes. This is done to increase the chance that at least one active ingredient is effective against gastrointestinal worms that have become resistant, or to delay resistance development by those worms that are still susceptible.
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, oxfendazole, etc.), levamisole, tetrahydropyrimidines (e.g. morantel, pyrantel) and other classic 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), that offer several weeks protection against re-infestation, depending on the delivery form and the specific parasite.
So far there are no reports on resistance of Toxocara vitulorum to the most common anthelmintics (benzimidazoles, macrocyclic lactones, levamisole, tetrahydropyrimidines, etc.) in contrast with many other gastrointestinal roundworms (e.g. Haemonchus spp, Cooperia spp, Ostertagia spp, Trichostrongylus spp), etc.
This means that if an anthelmintic fails to achieve the expected efficacy against Toxocara vitulorum, chance is very high that it is not due to resistance but to incorrect use, or the product was unsuited for the control of Toxocara vitulorum. Incorrect use is the most frequent cause of failure of antiaparasitic drugs.
Ask your veterinary doctor! If available, follow more specific national or regional recommendations for Toxocara vitulorum control.