Microbiology

An Overview of the Nematode Parasite Trichinella Spiralis



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Trichinella spiralis is a nematode parasite that gives rise to the disease ‘trichinosis’. It is probably the smallest nematode parasite causing diseases in humans and it is widespread throughout the world although the incidence of ‘trichinosis’ in the United States and many other developed countries has gone down due to better farming practices undertaken in raising domestic swine or in other words, pigs.

Why does Trichinella spiralis linked with pigs?

The nematode Trichinella spiralis is an interesting organisms in which the entire life cycle would take place within a single host and humans acquire the disease when they eat undercooked pork. Although these nematodes can exist in other animals such as rats and bears, the main route of infection for humans would be eating contaminated and undercooked pork.

What is the life cycle of this organism?

The infective form of the parasite usually resides in the striated muscles of the pigs in a specially accustomed cell known as the ‘nurse cell’. When the meat is consumed undercooked, these larval forms would be released from the ‘nurse cell’ in the stomach due to its acidity and the released larvae could penetrate into the intestinal lining and burrow within the tissue planes. Within the cell lining of the intestine, the larvae will acquire its adult form and would mate to produce around thousand five hundred eggs which will be released from the adult nematode only after hatching within the body of the Trichinella spiralis. After about six weeks of existence, adult parasite will die and it will allow the larvae to be released and burrow through the intestinal mucosa until they reach the blood vessels and the lymphatic tissues.

Once in the circulation, the larvae can feed on blood cells as well as travel to many parts of the body including heart, brain, and muscles. When it reaches the muscles, the larvae would encapsulate themselves within a muscle cell, which will now be referred to as, the ‘nurse cell’.

What are the symptoms associated with Trichinosis?

The manifestations related to Trichinosis would be particularly serious when the infection is heavy whereas light infection may even settle without any symptom at all. However, when symptoms do occur, it may result due to the intestinal damage, larval release, as well as intense inflammatory reactions taking place at the site where parasite larvae reside.

Thus, nausea, vomiting, diarrhea, and abdominal pain would be the initial signs, which may occur within 12 - 48 hours after consuming undercooked meat products infected with Trichinella. After 5 – 7 days, the patient may develop fever and facial oedema while serious manifestations may take place after 10 days following the initial exposure. Thus, among these serious manifestations, muscle pain, chest pain, breathing difficulties, shortness of breath, nerve disorders…etc could be highlighted.

What are the methods for diagnosing this infection?

A muscle biopsy is a sure way of making an accurate diagnosis whereas several immune fluorescent techniques for detecting the parasites are also available.

Can Trichinosis be treated in humans?

The treatment involves giving anti-parasitic agents such as albendazole and mebendazole along with medications such as hydrocortisone to counteract the intense inflammation. However, there effectiveness will depend on the heaviness of the infection as well as the organs involved in the inflammatory process. Pain relievers would also play a major part in managing these patients.

What are the preventive strategies for trichinosis?

In the US, the implementation of mandatory farming practices such as avoiding feeding pigs with uncooked garbage products as well as the voluntary disclosure of trichinella prevention strategies adapted by various farms have lessen the incidence as well as the deaths associated with trichinosis to negligible levels. At the same time, educating the public regarding the necessity to cook pork and store them in freezers for future use have also contributed to its decline in the United States.

References:

CDC - Trichinellosis Surveillance—United States—1997-2001

CDC - trichinellosis

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