With the exception of the tropics, where reports are rare, Trichinella spiralis can be found worldwide, especially among members of the meat – eating population. This organism can be found in a number of different animals, including pig, deer, bear, walrus and rat. The large number of temperature zones in which these animals find themselves suggests that Trichinella spiralis is resistant to most of the parasites studied to date in colder regions of the world. In developed areas, it is suspected that the delivery of contaminated pork to pigs is a major component of Trichinella spiralis transmission. Similarly, other animals contaminate this parasite by eating contaminated meat.
Morphology of Trichinella spiralis
The average juvenile, encapsulated larvae measure between 75 and 120 µm and 4 to 7 µm. A fully developed larva can reach a length of 1 mm.These larvae settle by winding themselves into muscle fibres and being encapsulated. Biopsies of these larvae often show a pronounced inflammatory infiltrate in response to the presence of the larvae.A striated muscle cell, called a nurse’s cell, surrounds the coiled larvae.
Although the small Trichinella spiralis worms have rarely been seen, they have been described.The female measures 4 x 0.5 mm, while the male is clearly smaller and measures 2 x 0.04 mm.The typical adult male typically has a thin anterior end with a small mouth, a long and thin digestive tract and a curved posterior end with two somewhat rounded appendages.The female differs from the male in two ways. The female has a blunt, rounded posterior end and a single ovary with a vulva in the anterior fifth of the body.
Life Cycle of Trichinella spiralis
Human infection with Trichinella spiralis is the result of human accidental infection with a parasite whose normal host is an animal (zoonosis).The infection is triggered after eating undercooked, contaminated meat, mainly striated muscle.The human digestion of meat releases Trichinella spiralis larvae into the intestine.Maturation to adult worms takes place quickly.Mating takes place and the gravid adult female migrates to the intestinal submucosa to lay her living larvae, as there is no egg stage in this life cycle.The infant larvae then enter the bloodstream and migrate into the striated muscle where they encyste the nurse cells.Over time, a granuloma forms, which calcifies around these cells. Since man is not the traditional host, the life cycle of the Trichinella spiralis is not completed and the cycle ends with the encystation of the larvae.
Clinical symptoms of trichinellosis
Trichinella spiralis is known as the great imitator because infected patients can suffer from a variety of symptoms that often imitate those of other diseases and conditions.Persons with a mild infection typically suffer from diarrhoea and possibly a mild fever, suggesting the flu.Heavily infected patients complain of symptoms such as vomiting, nausea, abdominal pain, diarrhea, headache and possibly fever during the intestinal phase of the infection.As the larvae begin their migration through the body, infected individuals experience a number of symptoms, including eosinophilia, pain in the pleural area, fever, blurred vision, edema and cough.In this phase death can also occur.Muscle discomfort, oedema, local inflammation, general fatigue and weakness usually develop when the larvae settle in the striated muscle and begin the inclusion process.The striated muscle of the face, limbs and other parts of the body can become infected.
Laboratory Diagnosis of Trichinellosis
Although clinical symptoms and patient history play a crucial role in the diagnosis of Trichinella spiralis infections, laboratory testing is essential to establish all suspicions.The examination of the affected skeletal muscle is the method of choice for the recovery of the encysted larvae.Serological methods are also available.Other laboratory findings, such as eosinophilia and leukocytosis, may also serve as indicators of disease.Increased serum muscle enzyme levels such as lactate dehydrogenase, aldolase and creatinine phosphokinase may also support the diagnosis of Trichinella spiralis.
It is important to note that multiple tests may be required to confirm the presence of Trichinella spiralis.No known test is 100 percent accurate.Combined with the fact that some tests for early infections can lead to false negative results, depending on when the sample is taken, it is often necessary to perform multiple tests.
Treatment of Trichinellosis
No medications are indicated if the infected person has a non –life-threatening strain of the disease.These patients are encouraged to get plenty of rest, supplemented with adequate hydration, antipyretic and analgesics.Patients with severe infections that can potentially be life – threatening are usually treated with prednisone.Thiabendazole can also be given, although previous research has shown that the efficacy of this drug is questionable.Under appropriate conditions, steroids may also be administered.
Prevention and Control of Trichinellosis
Thorough cooking of meat, especially of animals known to harbor Trichinella spiralis, is of paramount importance for the eradication of this parasite.It has been determined that proper storage of these meats, at below-zero temperatures (i.e., −15 ° C[ 59 ° F] for 20 days or −30 ° C[ 86 ° F] for 6 days) will greatly decrease the viability of the organism.In addition, avoidance of pork by pigs is also necessary to break the life cycle of the Trichinella spiralis.