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Presentation of Quiz #42

A 47-year-old female presented to her physician with a number of symptoms, beginning about three weeks before. Symptoms included malaise, followed by irregular fevers, chills, headaches and anorexia. The woman lived in Brazil and the previous year she had returned from a vacation to Africa, including Kenya, Tanzania, Uganda, and South Africa. She had seen a physician prior to returning to the United States and had received some antimalarial medication.  She was a wildlife photographer and writer and was often exposed to a number of life zones and resident plants, animals, insects, etc., both at home and on trips outside of Brazil.

Although both the patient and several others in the tour group remembered being bitten by insects, she was the only one who was symptomatic. On examination she was found to have several enlarged lymph nodes, which were soft, painless, and nontender.

Blood was drawn for routine hematology procedures and a specimen was also drawn to be sent to microbiology for examination as blood films stained with Giemsa stain or other blood stain. Based on her travel history, laboratory results revealed anemia, granulocytopenia, reduced platelets, and an increased sedimentation rate. Her gamma globulin level was elevated with a marked elevation of the IgM.

Please comment on the possible diagnosis related to the history of insect bites, the patient's clinical symptoms and the relative travel history. Extensive examination of thin blood films revealed the following:

1. Thin blood film

2. Thin blood film

3. Thin blood film

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Answer and Discussion of Quiz #42

The image presented in Diagnostic Quiz #42 is the following:

  1. Trypanosoma brucei gambiense trypomastigote (trypanosome)
  2. T. b. gambiense (note dividing forms - not seen in Trypanosoma cruzi infection)
  3. T. b. gambiense

Comments:

This was a case of African trypanosomiasis, probably caused by T. b. gambiense (West African Trypanosomiasis) based on travel history (various areas in Africa), the severity of symptoms, and overall description of the case. Although the woman lived in Brazil where Trypanosoma cruzi is found (cause of Chagas' disease, American Trypanosomiasis), the African trypomastigotes and the American trypomastigotes look quite different.

Trypanosoma cruzi

Trypanosoma brucei gambiense

There are over 55 million people in 36 countries at risk and approximately 50,000 new cases per year of African trypanosomiasis The African trypomastigotes (both East and West African trypomastigotes) (see right photograph above) have a very small kinetoplast (the dot at one end of the organism), while T. cruzi tends to have a very large kinetoplast that appears to go beyond the body of the organism (see left photograph above). Both organisms can actually be in a "C" shape; this alone does not indicate infection with T. cruzi.

Life Cycle:

Trypanosomal forms are ingested by the tsetse fly (Glossina sp.) when a blood meal is taken. Once the short, stumpy trypomastigote reaches the midgut of the tsetse fly, it transforms into a long slender procyclic stage. The organisms multiply in the lumen of the midgut and hindgut of the fly. After approximately 2 weeks, the organisms migrate back to salivary glands through the hypopharynx and salivary ducts, where the organisms attach to the epithelial cells of the salivary ducts and then transform to their epimastigote forms. In the epimastigote forms, the nucleus is posterior to the kinetoplast, in contrast to the trypomastigote, in which the nucleus is anterior to the kinetoplast. There is continued multiplication within the salivary gland, and metacyclic (infective) forms develop from the epimastigotes in 2 to 5 days. With development of the metacyclic forms, the tsetse fly is now infective. During the act of feeding, the fly introduces the metacyclic trypanosomal forms into the next victim in saliva injected into the puncture wound. The entire developmental cycle in the fly takes about 3 weeks and once infected, the tsetse fly remains infected for life.

The course of infection in African trypanosomiasis occurs in three stages. Soon after inoculation of the metacyclic trypanosomes by an infected tsetse fly, an inflammatory lesion develops at the site of inoculation; this lesion is called the trypanosomal chancre. Trypomastigotes then invade the local lymphatics and later the bloodstream. After a time, the organisms invade the choroid plexus and enter the brain and cerebrospinal fluid (CSF). There is quite a bit of variation between the two diseases caused by East African and West African trypanosomiasis. In the East African disease (T. b. rhodesiense), chancres are common, the hemolymphatic stage is severe, and rapidly progresses to a fatal meningoencephalitis, often within months of infection. With the West African form of the disease (T. b. gambiense), chancres are uncommon, the hemolymphatic stage may not be apparent, and meningoencephalitis progresses very slowly, often over several years, thus the "sleeping sickness" syndrome.

Antigenic Variation:

During the course of the infection, the number of trypomastigotes in the blood fluctuates. This relapsing parasitemia is due to the host's immune response to the parasites. Each decline in parasite number results from the antibody-mediated destruction of trypomastigotes bearing a particular variant surface glycoprotein (VSG). Each new wave of parasitemia represents the growth of a trypomastigote population expressing an antigenically different VSG. This process of ANTIGENIC VARIATION is a feature of all African trypomastigotes. Since each trypomastigote expresses only one VSG at a time and has as many as 1,000 different VSG genes, the number of different variable antigen types (VATs) that can be expressed during an infection is quite large. The continued response of the host to the new/different variable antigen types leads to elevated gamma globulins, particularly the IgM levels, including the CSF. Generally, if an immunocompetent individual does not have an elevated IgM, they almost certainly do not have African trypanosomiasis.

Key Points - Laboratory Diagnosis

  1. Trypomastigotes are highly infectious, and health care workers must use bloodborne pathogen precautions.
  2. Trypomastigotes may be detected in aspirates of the enlarged lymph nodes in addition to blood and CSF.
  3. Concentration techniques, such as centrifugation of CSF and blood, should be used in addition to thin and thick smears (Giemsa or Wright's stain).
  4. Trypomastigotes are in highest numbers in the blood during febrile periods.
  5. Multiple daily blood examinations may be necessary to detect the parasite.
  6. Blood and CSF specimens should be examined during therapy and 1 to 2 months posttherapy.
  7. NOTE:  Because of periodicity, parasite numbers in the blood may vary; therefore, multiple specimens should be collected and a number of techniques should be used to detect the trypomastigotes.
  8. Although not used within the United States, the card agglutination test for trypanosomiasis antibody (CATT/T. b. gambiense) is more sensitive than methods that require visualization of the trypomastigotes.
  9. Antigen detection methods are also available (ELISA), but are generally available primarily in areas of endemic infection.

References:

  1. Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.
  2. Warren, K.S. and A.A.F. Mahmoud.1990. Tropical and Geographical Medicine, 2nd ed., McGraw-Hill Inc., New York, NY.