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Presentation of Quiz #12

A 43-year-old immunocompetent female was admitted to the hospital in a confused, lethargic state. An adequate history was not possible; however, the patient had seen her physician about 10 days before complaining of headache, weakness, malaise and fever. She was treated for sinusitis; however, she failed to improve on this therapy. Her temperature continued to be elevated about 4-5 degrees. She became semi-stuporous and was hospitalized.

On examination, she was a well-developed, acutely ill female who was confused. The heart was normal, but the lungs exhibited rales at both bases. There was a wrist drop on the left and weakness of the flexor muscles of both arms and left leg. The patient had numerous splinter hemorrhages under the fingernails and periorbital edema.

Laboratory findings included a very high peripheral eosinophilia of 50%. The brain scan was normal and the CSF examination revealed normal pressure, clear fluid, and no cells or bacteria. Based on this information, a parasitic disease was suspected.

Please comment on the possible diagnosis related to the history, the patient's clinical symptoms and the laboratory test results to date. Examination of the patient revealed the following:

1. Splinter hemorrhages

2. Swollen eyes

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Answer and Discussion of Quiz #12

The images presented in Diagnostic Quiz #12 are the following:

  1. Splinter hemorrhages of the fingernails.
  2. Periorbital edema.

Comment: This is a case of a woman who was infected with Trichinella spiralis. Following admission, a detailed history was obtained. Approximately one month prior, the patient ingested raw pork which she had purchased and made into sausage. About one week later, she complained of diarrhea, muscle pain, neck discomfort and frontal headache, but was not seen by a physician. At the end of two weeks, her temperature was elevated; marked periorbital edema appeared, accompanied by severe frontal headache and profound weakness. At this time, the patient, suspecting sinusitis, consulted her physician. Antibiotics were not effective, additional neurological symptoms appeared, and she was hospitalized 22 days after ingestion of the raw pork.

Trichinella spiralis

Human infection is initiated from the ingestion of raw or poorly cooked pork, bear, walrus, or horse meat, or meat from other mammals (carnivores and omnivores) containing viable, infective larvae. The tissue is then digested in the stomach. The excysted larvae then invade the intestinal mucosa, develop through four larval stages, mature, and mate by the second day. By the sixth day of infection, the female worms begin to deposit motile larvae, which are carried by the intestinal lymphatic system or mesenteric venules to the body tissues, primarily striated muscle. Deposition of larvae continues for approximately 4 weeks, with each female producing up to 1500 larvae in the nonimmune host.

The very active muscles, which have the greatest blood supply, including the diaphragm, muscles of the larynx, tongue, jaws, neck, and ribs, the biceps, gastrocnemius, and others, are invaded. The encapsulated larvae reach lengths of 0.8 to 1 mm within the cyst capsule. The cyst wall results from the host's immune response to the presence of the larvae, and the encysted larvae may remain viable for many years, although calcification can occur within less than a year. As few as five larvae per g of body muscle can cause death, although 1,000 larvae per g have been recovered from individuals who died from causes other than trichinosis.

Pathological changes due to trichinosis can be classified as (i) intestinal effects and (ii) muscle penetration and larvae encapsulation. Any damage caused in either phase of the infection is usually based on the original number of ingested cysts. Symptoms that may develop within the first 24 h include diarrhea, nausea, abdominal cramps, and general malaise, all of which may suggest food poisoning, particularly if several people are involved. Studies also indicate that the diarrhea can be prolonged, lasting up to 14 weeks (average, 5.8 weeks) with little or no muscle symptomatology. It is still unknown whether this new clinical presentation is related to variant biological behavior of arctic Trichinella organisms, to previous exposure to the parasite, or to other factors.

During muscle invasion, there may be fever, facial (particularly periorbital) edema, and muscle pain, swelling, and weakness. The extraocular muscles are usually the first to be involved, followed by the muscles of the jaw and neck, limb flexors and back. Muscle damage may cause problems in chewing, swallowing, breathing, etc., depending on what muscles are involved. The most severe symptom is myocarditis, which usually develops after the third week; death may occur between the fourth and eighth weeks. Other severe symptoms, which can occur at the same time, may involve the central nervous system.

Although Trichinella encephalitis is rare, it is life threatening. Technological advances such as the computerized axial tomography scan, angiogram, and electroencephalogram are of no diagnostic assistance and probably add nothing to traditional diagnostic information, which includes eosinophilia, sedimentation rate, and muscle biopsy.

It is estimated that 10 to 20% of the patients with trichinosis have central nervous system involvement and that the mortality rate may reach 50% if these patients are not treated. Symptoms may mimic those of polyneuritis, acute anterior poliomyelitis, myasthenia gravis, meningitis, encephalitis, dermatomyositis, and polyarteritis nodosa. There may be focal paresis or paralysis (quadriplegia to single muscle group).

Peripheral eosinophilia of at least 20%, often over 50%, and possibly up to 90% is present during the muscle invasion phase of the infection. Fever can also be present at this time and persist for several days to weeks, depending on the intensity of the infection. However, once the larvae begin to encapsulate, patient symptoms subside, and eventually the cyst wall and larvae calcify.

Often the first clue is the patient's history of possible ingestion of raw or rare pork or other infected meat. There may also be other individuals from the same group with similar symptoms. Trichinosis should always be included in the differential diagnosis of any patient with periorbital edema, fever, myositis, and eosinophilia, regardless of whether or not a complete history of raw or poorly cooked pork consumption is available. If present, subconjunctival and subungual splinter hemorrhages also add support for such a presumptive diagnosis. If the meat consumption history is incomplete, food poisoning, intestinal flu, or typhoid may be suspected. It is very rare to recover adult worms or larvae from stool or other body fluids (blood, cerebrospinal fluid [CSF], etc.) if the patient has diarrhea.

Muscle biopsy (gastrocnemius, deltoid, and biceps) specimens may be examined by compressing the tissue between two slides and checking the preparation under low power of the microscope (10 x objective). However, this method does not become positive until 2-3 weeks after the onset of the illness. Muscle specimens or samples of the suspect meat can also be examined by using an artificial digestion technique to release the larvae.

Serologic tests are also very helpful, the standard two being the enzyme immunoassay (EIA) and the bentonite flocculation (BF) tests, which are recommended for trichinosis. The EIA is used for routine screening and all EIA-positive specimens are tested by BF for confirmation. A positive reaction with both tests indicates infection with T. spiralis within the last few years. Often, antibody levels are not detectable within the first month postinfection. The titers tend to peak in the second or third months postinfection and then decline over a period of a few years.

There is no specific recommended therapy for trichinosis. Thiabendazole has been used with limited success when given during very specific time frames. Mebendazole has also been tried on a limited basis. For encysted larvae, a long course of high-dose mebendazole appears to be more effective and better tolerated than thiabendazole. During muscle invasion by the larvae, corticosteroids may decrease the severity of the disease. Unfortunately, the disease is often finally diagnosed well after muscle invasion has begun. At this point, supportive therapy may be the only option.

Preventive measures for pork containing temperate zone strains would include refrigeration at 5 F (-15 C) for not less than 20 days, at -10 F for 10 days, or at -20 F for 6 days or deep freezing (-37 C). Smoking, salting, and drying are not effective. In 1981, the U.S. Department of Agriculture issued a news release that suggested that microwave cooking might not kill the larvae. On the basis of a number of subsequent studies, the current recommendation states that ``all parts of pork muscle tissue must be heated to a temperature not lower than 137 F (58.3 C)''. It has been recommended that an internal meat thermometer be used when one is cooking pork; the meat can be tested after being removed from the microwave oven if the oven is not equipped with an internal thermometer. Reduction in the number of cases is due primarily to regulations requiring heat treatment of garbage and low-temperature storage of the meat. Occasional outbreaks are frequently due to problems with feeding, processing, and cooking of pigs raised for home use.


Trichinella spiralis: larvae in muscle

Trichinella spiralisencysted larva


  1. Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.
  2. Garcia, L.S. 2009. Practical Guide to Diagnostic Parasitology, 2nd Ed., ASM Press, Washington, D.C.