The Case of a Tropical Disease and Its Treatment by Santanello and Rehg

Part II—The Diagnostic Dilemma

Adrian’s condition had deteriorated by the next day. His left eyelid was extremely swollen and he had developed a high fever. There was no way that Adrian could work. Alejandro was worried and decided that his brother needed to see a doctor. If Adrian could not work, their boss at the plantation might simply fire him. Alejandro helped Adrian walk to the highway where he could flag down a bus to Quepos, while Alejandro returned to the plantation.

After waiting for a few hours at a small clinic on the outskirts of Quepos, Adrian was seen by Dr. Rodriguez. The doctor was immediately suspicious that Adrian might have Chagas disease due to his swollen eyelid, a characteristic symptom known as Romaña’s sign (see Figure 1), and given that he lived in an area in which the disease vector was prevalent. Dr. Rodriguez took a blood sample from Adrian. Visual inspection of the blood with a thin blood film under a microscope confirmed the doctor’s initial guess. There were characteristic forms of the unicellular protozoan Trypanosoma cruzi in his bloodstream. These forms of the protozoan, known as trypomastigotes (see Figure 2), are present in the bloodstream of individuals in an acute stage of Chagas disease.

Dr. Rodriguez explained to Adrian that he had Chagas disease, caused by a type of trypanosome, which is a microscopic protozoan. While the disease can be transmitted through blood transfusion from an infected individual or from mother to child during pregnancy the most common form of transmission is through the bite of an insect vector, a type of triatomine insect, which is also known as the vinchuca or “kissing bug” (see Figure 3). Given that Adrian lived near the forest, the triatomine that infected him was likely Triatoma dimidiate. The doctor further explained that the bug serves as a host for the protozoan. When these bloodsucking bugs bite a human, the protozoan enters the human’s blood from the infected bug feces deposited at or near the bite. The vinchuca likes to bite people around the mouth or eyes because the skin is thinner there. If the bug is infected with T. cruzi and the bug feces get into the bite, another open cut, or into the eye, there is a good chance the person will become infected.

“Adrian, it is estimated that 17 million people throughout Central and South America are infected with this disease and that 50,000 will die annually. You have symptoms characterizing the acute stage of Chagas disease, and there is a small chance you could eventually die if your symptoms become severe enough. If instead you seem to get better, even without treatment, after years or even decades of being infected with the parasite you could develop serious problems in your heart or other internal organs from long-term infection. The protozoa will settle into your muscles, heart tissue, or intestines and you could eventually die from complications and damage to the organs. Once the parasites become established in your body, which is considered the chronic stage of the disease, it is nearly impossible to treat. We need to attempt to destroy all of the parasites in your body now.”

Dr. Rodriguez wanted Adrian admitted to a hospital for treatment, but Adrian was adamant that he would not go. “I do not want to be stuck in a hospital in Quepos, away from my brother.” Adrian did not speak out loud his other fears—that he would be fired from his job at the plantation and someone at the hospital might suspect he was in Costa Rica illegally. Dr. Rodriguez gave up trying to convince Adrian to admit himself to a hospital, and instead told Adrian that he must start medical treatment to destroy the protozoa. The doctor provided Adrian with a prescription for benznidazole, which is one of the only two drugs presently available to treat Chagas disease. The doctor warned Adrian about the need to take the medication on the prescribed schedule, as well as potential medication side effects, including sleeplessness, nausea, diarrhea, and skin rashes. The doctor also warned him that it was important to complete the full course of medication, or he was less likely to be cured.

“You will have to visit me for an additional serological blood test after you finish taking the medications to determine if there are any remaining protozoa in your body. Approximately 30 to 40% of individuals treated in the acute stage of Chagas disease may not be completely rid of the parasite following the initial course of medication.” Dr. Rodriguez continued, “If side effects of the drugs become very strong, you need to see me as soon as possible. The drugs are very potent, and could make you ill.”

The doctor knew about the condition of the houses around the fruit farms, and told Adrian, “Your house may be harboring more vinchucas, or new bugs may enter your house from the nearby forest and reinfect you. You will need to take measures to prevent additional bites from these insects.”

Adrian asked whether he could treat the disease with some pills he had remaining from a previous prescription for a skin infection. He also wondered if there was some kind of injection that could make him immune to the disease in the future. Dr. Rodriguez responded that the pills were probably a general bacterial antibiotic, which were not any use in treating the parasite. An injection wouldn’t have helped either. “Currently, there is no vaccine to prevent Chagas disease, and it is unlikely a vaccine will soon be developed. Your best option to prevent future infections is to not be bitten by any more vinchucas.” Dr. Rodriguez was himself frustrated at the lack of prevention and treatment options available for this disease, but could do nothing more than send Adrian on his way.

Background

Read the following references, which provide background information on Chagas disease, triatomes (kissing bugs), and medications for treatment.

• Information provided by the World Health Organization regarding Chagas disease at http://www.who.int/tdr/diseases/chagas/.
• Information on Triatoma dimidiata and control mechanisms by Ramsey and Schofield (2003).

• Information sheets from PharmGKB about the two standard medications for treating Chagas disease, benznidazole and nifurtimox:

  • http://www.pharmgkb.org/do/serve?objId=803&objCls=DrugProperties
  • http://www.pharmgkb.org/do/serve?objId=845&objCls=DrugProperties

Questions

1. How does the kissing bug (e.g., Rhodnius sp., Triatoma dimidiate) locate its human prey?
2. What type of environment does the kissing bug inhabit?
3. Given the behavior and ecology of this insect, what are some factors that could cause the incidence of Chagas disease to increase in Central and South America in areas like the banana plantation, and why?
4. What are some of the steps that can be taken to reduce the likelihood of infection by Chagas disease through insect vectors like kissing bugs?
5. Which of these approaches might be easiest, or most useful, for Adrian, given his circumstances?

References

Drugs.com

http://www.drugs.com/cons/Benznidazole.html Accessed on December 19, 2006.

Kroeger, A., E. Villegas, J. Ordoñez-González, E. Pabon, and J.V. Scorza. 2003. Prevention of the transmission of Chagas disease with pyrethroid-impregnated materials. American Journal of Tropical Medicine and Hygiene 68(3):307–311.

Luguetti, A. 1997. Etiological treatment for Chagas’ disease. Parasitology Today 13(4):127–128.

PharmGKB, The Pharmacogenetics and Pharmacogenomics Knowledge Base.

http://www.pharmgkb.org/do/serve?objId=803&objCls=DrugProperties

http://www.pharmgkb.org/do/serve?objId=845&objCls=DrugProperties Accessed on November 30, 2007.

Ramsey, J.M. and C.J. Schofield. 2003. Control of Chagas disease vectors. Salud Pública de Mexico 45(2):123–128.

Schofield, C.J. and J.P. Dujardin. 1997. Chagas disease vector control in Central America. Parasitology Today 13(4):141–144.

Sgambatti de Andrade, A.L.S., F. Zicker, R.M. de Oliveira, S. Almeida e Silva, A. Lugetti, L.R. Travassos, I.C. Almeida, S.S. de Andrade, J.G. de Andrade, and C.M.T. Martelli. 1996. Randomized trial of efficacy of benznidazole in treatment of early Trypansoma cruzi infection. The Lancet 348:1407–1413.

Smith, M.L. The Kiss of Death

http://www.cocori.com/library/eco/chagas.htm. Accessed on October 12, 2006.

Terminix web site:

http://www.terminix-triad.com/pestlibrary3.cfm?id=27&catname=2 Accessed on December 19, 2006.

Zeledón, R, V.M. Montenegro, and O. Zeledón. 2001. Colonization of man-made ecotopes by Triatoma dimidiata (Latreille, 1811) in Costa Rica. Memórias do Instituto Oswaldo Cruz 96(5):659–660.

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