The patient is an eighteen-year-old female who initially noted a swollen warm area on her left cheek accompanied by a low grade fever, headache, muscle aches, and other nonspecific symptoms. Two days later she was alarmed when her right eye became pruritic, swollen, and painful. The condition progressed, and the patient consulted with an ophthalmologist who believed the condition to be either an allergic reaction or a bacterial infection of the conjunctiva and eyelid. Antibiotics were prescribed. The patient did not respond to the therapy and three days later sought attention at a local emergency room for increasing fever and headaches, lack of energy, and shortness of breath with no additional symptoms. In the ER the attending physician inquired about recent travel. The patient noted that she had returned about two weeks before from an eco-tour to Costa Rica. She had slept in a modern facility under insect netting in Puerto Viejo Limon but had gone on a several day raft trip up the Pacure River. During this trip she slept on an open platform covered with an insecticide-treated net. She noted that the net appeared old and had several torn areas. She did not apply insect repellent (as she had been instructed) because what was available was “not organic.” She was referred to the infectious disease department for additional workup. Initial blood cultures and eye swabs showed only normal skin bacteria. Liver function tests noted a borderline abnormality. However, both electrocardiogram and transthoracic ultrasound disclosed a number of abnormalities suggestive of mild myocarditis. Analysis of her peripheral blood smear showed Trypanosoma cruzi organisms. The results were confirmed by the Center for Disease Control using PCR analysis. The patient was treated for four months with antiparasitic agents. The patient became negative by PCR analysis following three months of therapy.
Discussion
The case (based on one from the author’s affiliated hospital with many modifications, see references) demonstrates a typical presentation of acute Chagas disease in a returning traveler from Central America. Chagas disease (American trypanosomiasis) is caused by parasitization by the protozoa T. cruzi. It is a zoonotic infection with a multiplicity of both wild and domesticated mammalian hosts. The disease vector is triatomine insects (kissing bugs), which transmit the disease between animal hosts and humans. Triatomines are obligate, nocturnal, blood feeding insects that defecate after feeding. Infection occurs when infected feces are deposited on mucosal surfaces or at the site of the bite. Triatomine insects tend to infest thatch roofs, adobe and brick homes, and substandard dwellings. Oral transmission of fecally contaminated food, congenital infections, and transmission via infected blood products (now much reduced by blood screening) can also occur. In this case, the initial swelling was likely to be the site of an insect bite (a chagoma), which may show local parasite infection or may be the result of an immune reaction to the bite. Such swellings are of minor medical concern. Unilateral eye swelling is a typical sign/symptom of disease and infection of the conjunctiva by the organism. Of more concern is systemic infection by the organism, which can produce acute myocarditis and infection of the brain and its coverings. Treatment is critical as the disease may become chronic and lead to severe cardiac and gastrointestinal disease that are difficult or impossible to treat. Chagas disease is prevalent in South and Central America where it may produce more disability than malaria. Aggressive insect eradication programs for dwellings and donor blood screening programs have reduced disease frequency; however, deforestation has led to increased movement of insects to more heavily inhabited areas. Only a handful of autochthonous (indigenous) cases of insect vectored Chagas disease have been reported in the United States. This is quite surprising as both the insect vector and infected sylvatic (not domesticated, “wild”) mammalian animal hosts, which are the disease reservoirs, are common in the southern United States. In the Southeast raccoons, opossums, and armadillos serve as infected hosts; in the Southwest, woodrats and many other small mammals are infected. In addition, infected domestic dogs have been found in the South. Sylvatic animal dens are often colonized by the vector triatomine insects. Hence, the lack of “native” U.S. disease is likely related to the quality of housing and rarity of vector insect infestation. It is of interest that several of the “native U.S. cases” demonstrated triatomine insects in the dwelling.
Etiology and Pathogenesis
Travel-related infection by Trypanosoma cruzi producing acute Chagas disease characterized by cutaneous and ocular symptoms and mild myocarditis.
Questions
1. An essential part of taking a patient’s history is to question recent travel outside of the United States. Why is this information of particular relevance in cases of suspected parasitic disease?
2. Parasitic infestation is often considered to be insignificant in the United States. Cite examples of protozoal parasitic disease that have caused significant public health problems in the United States.
3. Several roundworm (nematode) parasites still frequently occur in the United States, particularly in children. What simple precautions can be taken to prevent infestation?