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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Tissue Nematodes

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Trichinosis : Clinical Aspects

One or two days after the host has ingested tainted meat, the newly matured adults pene-trate the intestinal mucosa, producing nausea, abdominal pain, and diarrhea.

TRICHINOSIS : CLINICAL ASPECTS

MANIFESTATIONS

One or two days after the host has ingested tainted meat, the newly matured adults pene-trate the intestinal mucosa, producing nausea, abdominal pain, and diarrhea. In mild in-fections, these symptoms may be overlooked, except in a careful retrospective analysis; in more serious infections, they may persist for several days and render the patient pros-trate. Diarrhea persisting for a period of weeks has been characteristic of T. nativa outbreaks following ingestion of walrus meat by the Inuit population of northern Canada. Larval invasion of striated muscle begins approximately 1 week later and initiates the longer (6 weeks) and more characteristic phase of the disease. Patients in whom 10 or fewer larvae are deposited per gram of tissue are usually asymptomatic; those with 100 or more generally develop significant disease; and those with 1000 to 5000 have a very stormy course that occasionally ends in death. Fever, muscle pain, muscle tenderness, and weakness are the most prominent manifestations. Patients may also display eyelid swelling, a maculopapular skin rash, and small hemorrhages beneath the conjunctiva of the eye and the nails of the digits. Hemoptysis and pulmonary consolidation are common in severe infections. If there is myocardial involvement, electrocardiographic abnormali-ties, tachycardia, or congestive heart failure may be seen. Central nervous system inva-sion is marked by encephalitis, meningitis, and polyneuritis. Delirium, psychosis, paresis, and coma can follow.

DIAGNOSIS

The most consistent abnormality is an eosinophilic leukocytosis during the second week of illness and persists for the remainder of the clinical course. Eosinophils typically range from 15 to 50% of the white cell count, and in some patients, this may induce extensive damage to the cardiac endothelium. In severe or terminal cases, the eosinophilia may dis-appear altogether. Serum levels of IgE and muscle enzymes are elevated in most clini-cally ill patients.

There are a number of valuable serologic tests, including indirect fluorescent anti-body, bentonite flocculation, and enzyme-linked immunosorbent assay. Significant anti-body titers are generally absent before the third week of illness, but may then persist for years.

Biopsy of the deltoid or gastrocnemius muscles during the third week of illness often reveals encysted larvae.

TREATMENT

Patients with severe edema, pulmonary manifestations, myocardial involvement, or central nervous system disease are treated with corticosteroids. The value of specific anthelmintic therapy remains controversial. The mortality of symptomatic patients is 1%, rising to 10% if the central nervous system is involved. Mebendazole and albendazole halt the production of new larvae, but in severe infection, the destruction of tissue larvae may provoke a hazardous hypersensitivity response in the host. This may be moderated with corticosteroids.

 

PREVENTION

 

Control of trichinosis requires adherence to federal feeding regulations for pigs, and limiting contact between domestic pigs and wild animals, particularly rodents, who might be carry trichinella larvae in their tissues. Domestically, care should be taken to cook pork to an internal temperature of at least 76.6°C, freeze it at –15°C for 3 weeks, or thoroughly smoke it before it is ingested. T. nativa in the flesh of arctic animals may survive freezing for a year or more. All strains may survive apparently adequate cooking in microwave ovens due to the variability in the internal temperatures achieved.

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