Parasitic Infections in Adults and Children: Trichinosis

Parasitic Infections in Adults and Children: Trichinosis

  Autor dr. Molfea Camelia Data: 13.01.2006

Parasitic Infections in Adults and Children: Trichinosis
The Nematodes are round, symmetric, elongated worms, being one of the most diverse types of animals. The most nematodes species live freely in the nature, but some have evolved and are not parasites of plants and animals, including of humans. The parasitic nematodes of medical importance are divided into intestinal nematodes and tissue nematodes, but this classification is not exact. 

The trichinosis occurs after the ingestion of infected pork or of meat of carnivores who contain cysts of Trichinella spiralis. Many infections are mild or without symptoms, but the massive infections may lead to severe enteritis (affection of the intestine), periorbital edema (swelling around the eyes), myositis (muscle infection) and death, in rare cases. 

Life cycle and epidemiology:

Nowadays there are five species of Trichinella which may cause infections in humans. Two species are spread globally: Trichinella spiralis which is found at a large variety of carnivors and omnivorous animals and Trichinella pseudospiralis which is present is mammals and birds. Trichinella nativa is present in Arctic regions and infects the bears; Trichinella nelsoni is present in eastern Africa and infects the feline predators and the hyenas and bush pigs; Trichinella bitovi is found in Europe and westers Asia in carnivores but not in domestic pigs.
After the host consumes meat infected with trichinella, the larvae cysts are released through acid digestion (the stomach digestion) and pepsin digestion (an enzyme discharged by the stomach). The larva invades the small intestinal wall and turns rapidly into adult worms. After a week, new larvae are produced, and they migrate to the skeletal muscle cells via the blood stream. The larvae of all species, except the Trichinella pseudospiralis, encyst by introducing a drastic change in the muscle cell architecture. Although the immune responses of the host body may help eliminating the adult worms, they have a reduced effect on the larvae found in the muscles. 
The most trichinosis in humans occurs after the ingestion of infected pork, and therefore they may appear in almost every place where pork is consumed, domestic or wild. In humans, the trichinosis can be taken from other animals too - dog meet in some Asian or African regions, horse meet in Italy or France, bear or walrus meat in Nordic countries. Although the cattle (herbivorous) are not usually hosts for Trichinella, the beef was also involved in the occurance of some epidemics, when it was infected or mixed with infected pork. 

Pathogenicity: strong 

The clinical symptoms of trichinosis occur both in adult and in children, because of the successive intestinal invasions of the parasite, of the larvae migration and of the muscle encystation. Most mild infections (under 10 larvae per a gram of muscles) have so symptoms, whereas the severe infections (over 50 larvae per muscle gram) may endanger the life. The invasion of the intestine by a large number of parasites may cause diarrhea occasionally, within the first week of infection. Abdominal pain, constipation, nausea and vomiting are other symptoms which might be accentuated. 
The prolonged and sudden diarrhea was observed in trichinosis in the Arctic regions, as a response to the repeated infection. 
The symptoms caused by the larvae migration and by the muscles invasion start showing in the second week after the infection. The Trichinella larvae which migrate, cause a reaction of local and system hypersensitivity, or fever. The facial edema (swelling of the face) and the periorbital edema (swelling around the eyes) might occur sometimes, as well as the subconjunctival hemorrhage. 
Sometimes, maculopapular rashes may occur (skin redness), headaches, cough, dyspnea (difficult breathing) or dysphagia (difficult swallowing). The myocarditis (inflammation of the heart muscle), with tachycardia or heart failure - and, less frequently, encephalitis (brain inflammation) or pneumonia might occur as the most important causes of death and trichinosis. 
After the larvae encystation in the muscles started, in about 2-3 weeks after the infection takes place, there are symptoms to occur, such as myositis with muscle pains, edema and muscles weakness and these usually appear as inflammatory reactions caused by the migrating larvae. The most affected muscles are the ocular ones, the masseter ones (the muscles which move the mandible), the neck muscles, the biceps, the low spinal muscles and the diaphragm, with the highest inflammation at 3 weeks after the contamination, the symptoms being gradually reduced after this, in a prolonged convalescence. 

Treatment:

The available anthelmintics are not enough for the Trichinella larvae in the muscles. Fortunately, the patients with milder infection get well without complications only by resting in bed, taking antipyretics (which reduce the fever) and analgesics (which reduce the pain). The glucocorticosteroids (hormones released by the suprarenal glands or medicine) such as prednisone (1mg/kg daily for 5 days) are helpful for the severe myositis and myocarditis. 
The larvae may be destroyed by cooking the pork until the meat is not red anymore, or by freezing it at -15 degrees for 3 weeks. However, the arctic larvae of Trichinella nativa in the bear and walrus meat are more resistant and may live even after freezing them. 
It is important, before consuming the pork, to be careful where you buy it from, to make sure it has the veterinary certification, and to give small quantities of meat to your children, after being cooked very well although it is a healthy meat. 



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