Oesophagostomum is a genus or parasitic roundworms belonging to the family called Strongylidae that affects cattle, sheep, goats and other ruminants, as well as pigs. It also infects wildlife (deer, antelopes, camels, monkeys, wild boars, etc.). It is found worldwide, but is more frequent in warm and humid climates in tropical and subtropical regions. As a general rule, within the mixed infections with gastrointestinal roundworms Oesophagostomum worms are usually not a predominant species.
These worms are called "nodular worms" because they cause the appearance of characteristic nodules in the large intestine of their hosts.
There are several species of veterinary importance, e.g.:
- Oesophagostomum brevicaudum. Found mainly in North America in swine.
- Oesophagostomum columbianum. Found worldwide mainly in sheep, goats and wild ruminants.
- Oesophagostomum dentatum. Found worldwide in swine and wild boars.
- Oesophagostomum multifoliatum. Found mainly in East and West Africa in sheep and goats.
- Oesophagostomum radiatum. Found worldwide, mainly in cattle, but also in sheep, goats and wild ruminants.
- Oesophagostomum venulosum. Found worldwide in livestock. Usually not pathogenic.
Oesophagostomum worms are mostly found mixed with other gastrointestinal roundworms (in ruminants Haemonchus, Cooperia, Ostertagia, Nematodirus, etc).
Neither dogs nor cats are affected by this species.
Some species of this genus (e.g. Oesophagostomum bifurcum, usually a parasite of monkeys) are also human parasites, mainly in West Africa.
The disease caused by Oesophagostomum worms is called oesophagostomiasis.
Is livestock infected with Oesophagostomum worms contagious for humans?
- Probably NO. Direct contact with livestock or their fresh feces is most likely not contagious for humans because the eggs shed with the feces have to mature in the environment to become infective. For more details about the life cycle of these worms see below.
Final location of Oesophagostomum worms
Predilection site of adult Oesophagostomum worms is the large intestine.
Anatomy of Oesophagostomum worms
Adult Oesophagostomum worms are 15 to 20 mm long, whereby females are larger than males. The head of Oesophagostomum worms has a prominent cephalic vesicle, which may be constricted at several points depending on the species. As other roundworms the body of these worms is covered with a cuticle, which is flexible but rather tough. The worms have no external signs of segmentation. They 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. 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, have a thin shell, measure ~40-60x70-100 micrometers and contain several cells, depending on the species.
All Oesophagostomum specieshave a direct life cycle, i.e. there are no intermediate hosts involved. Adult females lay eggs in the large intestine 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 1 week, depending on temperature and humidity. The eggs are susceptible to dryness and extreme temperatures, but can survive up to 3 months on pasture.
Livestock becomes infected after ingesting such larvae while grazing or with contaminated soil. Infection is also possible indoors through contaminated feed or bedding, seldom through licking of walls or objects where L3 larvae can climb by very high humidity. Ingested larvae penetrate into the intestinal mucosa and form nodules. About a week later they abandon the nodules and migrate to the colon, where they complete development to adults and reproduce. A few larvae may cross the gut's wall and migrate to the liver across the abdominal cavity.
The prepatent period (time between infection and first eggs shed) is 5 to 6 weeks.
Harm caused by Oesophagostomum worms symptoms and diagnosis
Oesophagostomum radiatum is very harmful for cattle, especially for stock younger than 2 years: massive infections can be fatal. The same applies to Oesophagostomum columbianum for lambs.
Infective larvae penetrate the intestinal wall and the host's organism reacts building nodules the size of a pea. This disturbs considerably the physiology of the gut, particularly the absorption of liquids, which causes diarrhea, but also the peristaltic movements. Digestion and defecation can be affected, and enteritis is possible. Deadly bacterial infections can happen if larvae migrating to the liver across the abdominal cavity, or if the nodules burst towards the abdominal cavity.
Oesophagostomum venulosum is rather benign and little is know about the pathogenicity of Oesophagostomum multifoliatum.
Oesophagostomum dentatum is one the most harmful roundworms in swine, more frequently in animals kept outdoors, particularly in piglets. Acute infections cause fever, loss of appetite and weight, colitis, aqueous or mucous diarrhea (green or dark). Chronic infections cause anemia and swellings (edema), in addition to diarrhea, which considerably weakens the animals.
Diagnosis is confirmed through detection of characteristic eggs in the feces.
Prevention and control of Oesophagostomum infections
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 about 1 week, removing all manure in shorter intervals can break the life cycle and reduce the infectivity of the environment. Other preventative measures are the same for all gastrointestinal roundworms and are explained in a specific article in this site (click here).
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.
Numerous broad spectrum anthelmintics are effective against adult worms and larvae, 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).
A few other narrow-spectrum anthelmintics such as closantel, nitroxinil and tetrahydropyrimidines (e.g. morantel, pyrantel) are effective against adult worms but may not control larvae and other roundworm species that often infect livestock simultaneously with Oesophagostomum worms.
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.
In some countries (e.g. Australia, Argentina, EU, New Zealand, Uruguay) monepantel, an anthelmintic of a new chemical class, is also available as a drench for use on sheep. It is effective against Oesophagostomum venulosum. It is not approved for cattle or goats.
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 Oesophagostomum and other gastrointestinal worms that have become resistant, or to delay resistance development by those worms that are still susceptible.
Excepting slow-release boluses, most wormers containing benzimidazoles (e.g. albendazole, febantel, fenbendazole, flubendazole, mebendazole, 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) 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 Oesophagostomum worms, in spite of abundant research on this subject. To learn more about vaccines against parasites of livestock and pets click here.
Biological control of Oesophagostomum (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 Oesophagostomum worms to anthelmintics
There are reports on confirmed resistance of Oesophagostomum radiatum worms to most used anthelmintics (benzimidazoles, ivermectin, levamisole, etc) in cattle and of Oesophagostomum columbianum in sheep. However, so far resistance of these worms seems to be less strong and widespread than resistance to other gastrointestinal roundworms (e.g. Haemonchus spp, Cooperia spp, Ostertagia spp, etc.). There are also some reports on resistance of Oesophagostomum dentatum to benzimidazoles, levamisole and pyrantel in pigs.
This means that if an anthelmintic fails to achieve the expected efficacy against Oesophagostomum worms, there is a significant risk that it is due to resistance to anthelmintics, particularly in sheep, goats and cattle. Nevertheless, it is well 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 Oesophagostomum control.