The incubation period for trichinellosis lasts from 2 to 50 days, depending on the number of infective larvae ingested (a greater number of larvae correspond to a shorter incubation period). The acute stage of trichinellosis corresponds to the phase in which the newborn larvae migrate from the lymphatic vessels and invade the muscle cells. The acute stage can be preceded by loose stools or diarrhea, with flatulence, moderately intense abdominal pain, loss of appetite, and vomiting.
The principal manifestations of the acute stage are fever, eyelid and periocular edema, and muscle pain. The onset of the acute stage is sudden, beginning with general weakness, chills, headache, fever (up to 40°C), excessive sweating, and tachycardia. In nearly all cases, these symptoms are followed by symmetrical eyelid and periocular edema, and edema frequently affects the entire face. In some persons, petechiae, intraconjunctival hemorrhages, and hemorrhages of nail beds occur. These symptoms are accompanied by eosinophilia (up to 19,000 cells/pL) and leukocytosis (up to 15,000-50,000 cells/ mL). Although eosinophilia appears early (i.e., before the development of clinical signs and symptoms), it increases between 2 and 5 weeks after infection. Leukocytosis, although not as common as eosinophilia, is characteristic of the acute stage of trichinellosis, and it indicates the presence of inflammation. This symptomatology is followed by pain in various muscle groups, which may restrict motility. Both creatinophosphokinase and lactate dehydrogenase activities have been observed in 75-90% of infected persons, and they peak earlier with respect to anti-Trichinella antibodies. The principal electrolyte disturbance is hypokalemia, which results in reduced muscle strength and cardiac disturbances, as revealed by ECG. Decreased levels of proteins and albumin result in a hydrostatic edema. Trichinellosis can also cause miscarriage or premature delivery, although infected women have delivered healthy babies. When infection is severe, complications such as cardiovascular, neurological, respiratory, and digestive disturbances can occur and hospitalization is compulsory. Twenty deaths have been documented worldwide out of a total of 10,030
It has not been possible to determine whether or not individual Trichinella species have specific clinical or biological patterns; this is because the number of infective larvae ingested has remained unknown in most cases, making it impossible to establish whether the clinical patterns observed were related to the species or to the infective dose. Nonetheless, T. spiralis infection, which is the cause of most human infections, is believed to be more severe than T. britovi infection, possibly because
T. britovi females are less prolific. In fact, in T. britovi-infected persons, only asymptomatic, mild, and moderate infections have been reported. In Trichinella nativa infections, there is a greater involvement of the intestine, with severe diarrhea. T. murrelli seems to be more likely to provoke skin reactions and less likely to cause facial edema. T. pseudospiralis seems to cause signs and symptoms that last longer.
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