While most parasites attack their host through the digestive system, a couple varieties do eventually work their way into the host's muscle tissue. The two most common types of parasitic muscle infections are trichinosis, also called trichinellosis, and cysticercosis. Trichinosis has more than one phase with unique symptoms in each phase while cysticercosis has only one set of symptoms.
The first phase of trichinosis is characterised by extremely subtle, or even no, symptoms. But if you swallow enough of the parasite's larvae, they will first penetrate the intestine and grow into adults. Once they are fully grown, they will mate and multiply. At this point in the infection, symptoms include diarrhoea, abdominal cramps, fever and/or general feeling of malaise. These will come about one to two days after infection has taken place.
The next phase of trichinosis is when the parasites finally migrate out of the intestines and into the other parts of the body. These symptoms will start around two to eight weeks after the initial exposure. The adult parasites will enter the bloodstream and begin embedding themselves into body tissues, mostly the muscle. Symptoms at this point include headache, fever, chills, cough, eye swelling, aching joints and muscle pain, itchy skin, diarrhoea or constipation. The severity of these symptoms will vary depending upon the level of infection. In extreme cases, motor coordination as well as heart and breathing problems may occur. Some infections will subside on their own within a few months. However, some severe infections can lead to death.
Cysticercosis is also caused by a parasite, the pork tapeworm. The tapeworm larvae enter the body and form cysticerci, or cysts. Usually, the cysts develop in the muscles. However, they can also form in the eyes as well as the brain. When they form in the brain, the condition is called neurocysticercosis. When cysticercosis happens in the muscles, symptoms rarely occur. The only way to tell if you have an infection is to feel for lumps underneath your skin.