Tag Archives: nematodes

Friday Fellow: Large Roundworm of Pigs

by Piter Kehoma Boll

It’s time to go back to the roundworms and to the parasites once more. Probably one of the most famous roundwors is the large roundworm of humans, Ascaris lumbricoides, but today I’m going to talk about its closest relative, the large roundworm of pigs, Ascaris suum.

Found worlwide, the large roundworm of pigs, as its name implies, infects pigs. It is a large worm of the phylum Nematoda and is very similar to the large roundworm of humans, the main difference being simply that the former infects pigs and the latter infects humans.

800px-asuum_male_and_female

A typical male (top) and female (bottom) of Ascaris suum. Photo by Wikimedia user VlaminckJ.*

The adult worms live in the intestine of pigs and show sexual dimorphism. Males are smaller, measuring 13–31 cm in length and have a curled posterior end. Females are larger, measuring 20–49 cm and do not have the curled posterior end. They have a light pink to whitish color and may occur in large quantities inside the host.

When sexually mature, a female can lay up to 200 thousand eggs per day and have up to 27 million eggs in its uteri. The eggs are eliminated with the pig feces and remain in the environment where the embryo starts its development. As soon as the eggs are eaten by a pigg, the eggs hatch and the larvae crawl into the walls of the large intestine and reach the bloodstream, being carried to the liver and from there to the lungs. In the lungs, they reach the alveoli and start to migrate upward toward the trachaea and are coughed up and swallowed by the pig, reaching the intestine again. There, they remain in the small intestine and complete their development into adults.

The great similarity of Ascaris suum and Ascaris lumbricoides implicate that they have a recent common ancestor which may have split into the two species after humans started to raise pigs. Eventually Ascaris suum may also infect humans and Ascaris lumbricoides may infect pigs too, but they seem to have a preference and an improved development in their “traditional” host. Molecular studies indicate that the populations of both species seem to be considerable isolated, but there have been some eventual hybridizations, suggesting that they are yet in the process of become fully separate species.

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References:

Leles, D.; Gardner, S. L.; Reinhard, K.; Iñiguez, A.; Araujo, A. (2012) Are Ascaris lumbricoides and Ascaris suum a single species? Parasite and Vector5: 42. https://dx.doi.org/10.1186/1756-3305-5-42

Wikipedia. Ascaris suum. Available at: < https://en.wikipedia.org/wiki/Ascaris_suum >. Access on November 6, 2017.

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Friday Fellow: Brown-gutted Mud Roundworm

by Piter Kehoma Boll

If you have your face buried in the mud at the bottom of a European lake, you may end up finding some of those tiny little roundworms known as Monhystera stagnalis. As usual, there is no common name for this species, but I decided to call it brown-gutted mud roundworm. Why? Because it lives in the mud and has a reddish-brown gut.

monhystera_stagnalis

An individual of Monhystera stagnalis. Photo by Marco Spiller.*

The brown-gutted mud roundworm is a widely distributed roundworm species, being common especially throughout Europe. It inhabits the fine sediments at the bottom of freshwater bodies, both stagnant and flowing, where it feeds on the organic material deposit in this medium, having a special taste for bacteria. It is able to survive in moderate organic pollution, but is sensitive to low oxygen levels.

It is one of the most common nematode species in its environment and it is very small, measuring around 1 mm in length, females being slightly longer than males. They are found in all depths of the sediment and seem to have a preference for staying closer to the surface during winter and deeper in the mud during summer.

Females are ovoviviparous, meaning that they retain the egg inside their bodies until they hatch, so they are pregnant with eggs. Although we are used to think that invertebrates produce hundreds or thousands of eggs at once, this is not the case with the brown-gutted mud roundworm. Females are usually pregnant of a single egg, sometimes with two or three. They are modest worms.

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ResearchBlogging.orgReferences:

Pehofer, H. (1989). Spatial Distribution of the Nematode Fauna and Production of Three Nematodes (Tobrilus gracilis, Monhystera stagnalis, Ethmolaimus pratensis) in the Profundal of Piburger See (Austria, 913 m a.s.l) Internationale Revue der gesamten Hydrobiologie und Hydrographie, 74 (2), 135-168 DOI: 10.1002/iroh.19890740203

Traunspurger, W. (1996). Autecology of Monhystera paludicola De Man, 1880 – Seasonal, Bathymetric and Vertical Distribution of a Free-living Nematode in an Oligotrophic Lake Internationale Revue der gesamten Hydrobiologie und Hydrographie, 81 (2), 199-211 DOI: 10.1002/iroh.19960810205

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Friday Fellow: Heartworm

by Piter Kehoma Boll

Life is not composed only by beautiful and cute creatures. Parasites form a big part of life. In fact, it is likely that there are more parasitic species than non-parasitic ones.

The heartworm (Dirofilaria immitis) is one of these not-so-cute species. A species of roundworm, it infects small mammals, especially dogs, and is spread by mosquitoes.

The name heartworm comes from the fact that this worm lives in the heart and pulmonary arteries of dogs during its adult stage. The result of the infection may be heart failure and damage on the heart and the arteries, but some infections may pass completely unnoticed, especially in sedentary dogs.

Not a pleasant view. Heartworms in a dog's heart. Photo by Alan R Walker*.

Not a pleasant view. Heartworms in a dog’s heart. Photo by Alan R Walker*.

After males and females mate in the heart of the dog, females give birth to live larvae called microfilariae. These are released in the bloodstream and await for being transfered to a bloodsucking mosquito during a bite. Over 60 species of mosquitoes are known to serve as intermediate hosts of microfilariae.

Inside the mosquito, the microfilariae grow from the larval stage L1 to the larval stage L3 and then migrate to the mosquito’s salivary glands and, once it bites another dog, they are transferred to it and develop under the skin at the site of the bite to the stage L4. Now the L4 larve migrate to the dog’s muscles and develop into the stage L5. Finally, they start to migrate through the bloodstream until they reach the heart and the pulmonary artery, where they mold into adults and the cycle is complete.

We may find such worms disgusting, but we must admit that they have a complex and amazing life.

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References:

Wikimedia. Dirofilaria immitis. Available at: < https://en.wikipedia.org/wiki/Dirofilaria_immitis >. Access on June 7, 2012.

Ludlam, K. W.; Jachowski, L. A.; Otto, G. G. 1970. Potential vectors of Dirofilaria imiitis. Journal of the American Veterinary Medical Association, 157: 1354-1359.

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