Genetic Confirmation of Atovaquone-Proguanil–Resistant Plasmodium falciparum Malaria Acquired by a Nonimmune Traveler to East Africa
- 1Center for Geographic Medicine and Department of Medicine, Chaim Sheba Medical Center, Tel Hashomer, Israel
- 2Tropical Disease Unit, Division of Infectious Diseases, Department of Medicine, Toronto General Hospital and the University of Toronto, Canada
- Reprints or correspondence: Dr. Kevin C. Kain, Toronto General Hospital, 200 Elizabeth St., EN G-224, Toronto, ON, Canada M5G 2C4 (Kevin.Kain{at}uhn.on.ca).
Abstract
We report a case of atovaquone-proguanil–resistant Plasmodium falciparum malaria acquired by a nonimmune traveler to Kenya. Recurrent parasitemia occurred 30 days after directly observed therapy with a combination of atovaquone and proguanil. Treatment failure was confirmed by genetic fingerprinting and sequencing. The primary isolate had wild-type sequence of cytochrome b; however, the recrudescent isolate had a single mutation at position 268 (Tyr268Ser).
Emerging drug resistance, as well as real and perceived intolerance to current antimalarial agents, has highlighted the need for new antimalarial drugs [1]. The combination of atovaquone and proguanil is the most recent antimalarial approved by the US Food and Drug Administration. Concerns have been raised regarding the potential development of resistance to atovaquone and proguanil [2]. Although clinical treatment trials have not, to date, identified confirmed cases of resistance, these studies have largely been performed among semi-immune populations residing in areas where malaria is endemic and where underlying immunity may facilitate the clearance of drug-resistant parasites and confound the interpretation of treatment outcome.
Postmarketing surveillance for drug-resistant malaria acquired by nonimmune travelers can be an important sentinel system for detection of emerging drug resistance [3, 4]. Using travelers as a surveillance system provides a mechanism to study large numbers of individuals returning from diverse areas where malaria is endemic. Because travelers are generally nonimmune, interpreting the outcome of antimalarial therapy is not confounded by reinfections or preexisting immunity, which is often present in residents of areas where the disease is endemic. We report here a case of genetically confirmed atovaquone and proguanil–resistant Plasmodium falciparum malaria acquired by a nonimmune traveler to East Africa. This study was reviewed and approved by the internal review board of the Toronto General Hospital.
During January 2002, a 24-year-old woman traveled to Mombasa, Kenya, for a 1-week vacation. She did not use chemoprophylaxis. Ten days after returning home to Israel, she developed fever. The results of malaria smears performed at admission to the hospital (1-week after the onset of symptoms) demonstrated 3% P. falciparum parasitemia. She received directly observed therapy with atovaquone and proguanil (Malarone [GlaxoSmithKline], 4 tablets each day for 3 days given with food; each tablet is equivalent to 250 mg of atovaquone and 100 mg of proguanil hydrochloride) and experienced no vomiting or diarrhea. She defervesced, and malaria smears were negative for P. falciparum by day 4 of hospitalization. Fever recurred 30 days later, and malaria smear results again demonstrated P. falciparum asexual parasites. DNA samples were extracted from the malaria isolate obtained at presentation and from that obtained on the day of recurrence using Qiagen columns (Qiagen) according to the manufacturers' instructions. The gene encoding the merozoite surface protein (MSP)-1 was amplified by PCR and subjected to genetic fingerprinting with single-strand conformational polymorphism (SSCP) analysis, as described elsewhere [5]. The primary isolate was monoclonal, and the recurrent isolate had an identical SSCP fingerprint, confirming true treatment failure [5]. The patient's illness was successfully treated with oral quinine (600 mg t.i.d. for 3 days) and doxycycline (100 mg b.i.d. for 7 days).
Atovaquone binds to the parasite mitochondrial cytochrome bc1 complex, inhibits electron transport, and collapses mitochondrial membrane potential [6]. Resistance has been linked to mutations in the cytochrome b gene [7]. Therefore, parasite DNA samples were extracted from the malaria isolate obtained at presentation and from the isolate obtained on the day of recurrence, as above, and the cytochrome b and dihydrofolate reductase genes were amplified by PCR and sequenced to detect mutations [4, 7]. The day 0 isolate had wild-type sequence of cytochrome b; however, the recrudescent isolate had a mutation at position 268 specifying a change from tyrosine to serine. Both isolates had mutations in the dihydrofolate reductase gene associated with resistance to cycloguanil, the active metabolite of proguanil [4]. The Tyr268Ser mutation observed in our case has been reported once before following atovaquone monotherapy, and in that instance it resulted in clinical failure and a 9364-fold increase in the IC50 of atovaquone [8]. This mutation has not previously been reported following atovaquone and proguanil combination therapy. However, a previous case of atovaquone and proguanil treatment failure was recently reported for a Nigerian man who had visited West Africa without prophylaxis. No day 0 isolate was available for analysis in this case, but the recrudescent isolate contained a Tyr268Asn mutation [9].
Our patient's case documents that resistance to atovaquone and proguanil may emerge during therapy and suggests that the synergistic interaction between atovaquone and proguanil is lost following mutations in parasite cytochrome b. It also supports the strategy of using travelers as a sentinel molecular surveillance system for emerging drug-resistant malaria.
Footnotes
-
Financial support: This work was supported by the Canadian Institutes of Health Research (CIHR, MT-13721). K.C.K. is supported by a Career Scientist Award from the Ontario Ministry of Health and a Canada Research Chair (CIHR).
- Received January 7, 2003.
- Revision received March 5, 2003.
- © 2003 by the Infectious Diseases Society of America
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