Threadworm (trichinella spiralis). A small nematode – females grow 3mm long and males about 1,5mm. Mature forms of the threadworm develop in the small bowel within several days from swallowing invasive larvas. On the sixth day from the infection, the females start to produce larvas which move into the tissue through the blood and lymph. The larvas develop in the muscle tissues and within 6 weeks they encyst. A certain amount of larvas survive in the human organism for dozen or so years.

Trichinosis, caused by threadworms, occurs on all continents where people eat animal meat which may contain the threaworms. The animals which can cause the infection are: pigs, wild boars, bears, dogs, cats and rats. However it is the most dangerous to eat dishes made of raw or undone meat.

Sanitary negligence and lack of hygiene (feeding pigs with carcass, presence of rats) are the most common causes of trichinosis. The majority of infections among men are caused by eating raw meat containing nomatodes. Most of them show no symptoms. Even if the symptoms are visible it still does not mean the disease is serious or light.