Parasitic Helminthology

Nematod Caenorhabditis elegans in movement

The word helminth, worm, is commonly used in Parasitology. Two phylae of helminths are important in Parasitology: flatworms, and nematodes, roundworms (in old and alternative classifications appear in the Aschelminth phylum).

Platyhelminthes are flatworms, most are hermaphrodites and many are parasitic. Clonorchis sinensis affects more than 30 million people worldwide, especially in Asia. It is caused by consuming fresh or semi-processed fish or shellfish. The genus Opistorchis has a similar behavior, affecting, in addition to the human species, other mammals and fish.

Fasciola hepatica is a parasitic worm of the bile ducts and gallbladder of numerous species, including human. In livestock, it is one of the most widespread parasites in ruminants, especially cattle, goats and sheep, although it can also affect horses and lagomorphs. Its intermediate hosts are aquatic snails.

Schistosomiasis is produced by trematodes of the genus Schistosoma. It is not usually a serious illness, although it is incapacitating, mainly by the fever. Its biological cycle is typical of the trematodes, alternating in the same species of vertebrates and invertebrates.

Life cycle of Schistosoma

Taenia solium is transmitted to humans through uncooked or undercooked pork enters the human species generally through pork, while Taenia saginata does it for beef. Humans are generally infected for eating raw or undercooked beef which contains the infective larvae, called cysticerci.

The hydatid cyst is produced by Echinococcus granulosus. It is hydatidosis, which occurs in human species and certain animals, such as the dog and the sheep. It is produced by ingesting food contaminated by feces that contain the parasite. The disease can become deadly, as cysts can affect the liver, lungs, bones, kidneys or brain.

Hydatid cyst in lamb's liver

Nematodes form a large part of the planet's biomass and are critical to maintaining ecosystems. Parasite nematodes are a minority group of all nematodes.

Trichuriasis, also known as whipworm infection, is caused by the nematode Trichuris trichiura, which is characterized by gastrointestinal problems and diarrhea.

Trichinosis is produced by nematodes of the genus Trichinella through eating undercooked meat containing Trichinella cysts, most often this is pork but can also occur from bear and dog meat. This causes muscle pain, fever and gastrointestinal disorders. When the parasite reaches the heart, the consequences can be lethal or cause heart problems. If the infestation is massive it can cause death by the traumatic effect of the invasion of the tissues. For this reason, pork should not be consumed, if not analyzed with the trichinoscope, a microscope adapted for this purpose.

Trichinella spiralis, enrrollada en forma de espiral, de donde le viene el nombre

Trichinella spiralis, in muscle tissue

Strongyloides stercoralis produces strongyloidiasis. It is a common nematode in warm and humid areas. Strongyloidiasis is an important disease in immunocompromised persons and can cause a hyperinfection syndrome that can lead to death if untreated. It's produced by the contact of soils contaminated with feces.

Ancylostoma duodenale is a nematode that causes the hookworm infection, together with Necator americanus. It's one of the most frequent parasitosis in the world, which is contracted by the skin or orally in places of poor hygiene.

Ascaris lumbricoides causes ascariasis, in which the multiplication of helminths in the intestine causes health problems, such as diarrhea, pallor, malnutrition, etc. They may cause visceral damage, peritonitis, inflammation, appendicitis, intestinal obstruction, or migrate to other organs. The genus Toxocara affects several species, in addition to the human, such as canids and felids; In animals larvae migrate throughout the body and only affect the human species if the number of larvae is very high and the individual is immunosuppressed. Anisakis are parasites of fish that can affect the human species; Have proliferated in recent times, perhaps because of bad fishing practices (such as throwing guts into the sea) or changes in weather conditions.

The pinworm, also known as threadworm in the United Kingdom and Australasia or seatworm, is the specie Enterobius vermicularis, that causes pinworm infection, also known as enterobiasis, a disease spread all over the world, mainly affecting children under 12 years old, who spread the disease by scratching the anus by itching, extending the eggs of the parasite.

Filarias are parasitic nematodes that cause terror. Wuchereria bancrofti and Brugia malayi are transmitted through the mosquito bite, living in the lymphatic system and causing an enormous dilation of the tissues. Loa loa is transmitted through the sting of horseflies, living in the subcutaneous tissue. Onchocerca volvulus causes onchocerciasis, which is transmitted through the black fly, microfilariae move through the body and if they reach the eyes can cause blindness. Dranunculus medinensis (in the photo below) affects the subcutaneous tissues and causes dracunculiasis, is transmitted by ingesting contaminated water.