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Local Transmission of Plasmodium vivax Malaria --- Virginia, 2002

Malaria transmission in the United States was largely eliminated during the mid-20th century; however, sporadic cases of locally acquired mosquito-transmitted malaria continue to occur. Since 1997, four separate probable mosquito-transmitted malaria outbreaks have been reported to CDC, including one from Virginia (1--3). This report describes the investigation of two cases of Plasmodium vivax malaria that occurred in northern Virginia in August 2002, and underscores the need for clinicians to consider the possibility of malaria in patients with fever of unknown origin.

Case Reports

Case 1. On August 23, 2002, a person aged 19 years from northern Virginia sought medical care at a family health clinic with a 4-day history of fatigue, fever, and chills. The patient also complained of muscle aches and sinus pain. A sinus infection was diagnosed, and the patient was prescribed azithromycin and desloratadine. Four days later, the patient returned to the clinic with additional symptoms, dizziness, and nausea. On physical examination, the patient had a temperature of 103.5º F (39.7º C) and tachycardia. Laboratory results revealed pancytopenia (platelet count: 61,000/µL [normal: 130,000--400,000/µL], hemoglobin: 10 g/dL [normal: 11.5--16.0 g/dL], and white blood cell count: 3,300/µL [normal: 4,000--11,000/µL]). The patient's therapy was changed to oral levofloxacin. Malaria parasites were identified subsequently on a routine complete blood count smear taken 4 days after the initial clinic visit. The patient was contacted and administered chloroquine. A review of the initial malaria smear by a local university hospital confirmed the diagnosis of P. vivax malaria. The patient completed a 3-day course of chloroquine therapy and after a normal glucose-6-phosphate dehydrogenase (G6PD) test result was placed on primaquine for 14 days. The patient had complete resolution of symptoms.

Case 2. On August 25, a person aged 15 years from northern Virginia was taken to a local emergency department for treatment of 2 weeks of headaches and 4 days of fever, nausea, vomiting, malaise, and nose bleeds. On physical examination, the patient had a temperature of 105.0º F (40.6º C), tachycardia, splenomegaly, and jaundice. Laboratory values revealed pancytopenia (platelet count: 48,000/µL, hemoglobin: 11.6 g/dL, and white blood cell count: 3,200/µL). A malaria smear revealed Plasmodium sp. parasites reported initially as nonfalciparum. The patient was admitted to the hospital and administered quinine and clindamycin. The smear was confirmed subsequently as P. vivax by the Virginia Department of Health. The patient's physician contacted CDC for treatment recommendations on August 28 because the patient had tinnitus, requiring discontinuation of the quinine. The patient completed a 3-day course of chloroquine therapy and was discharged with complete resolution of symptoms on August 31. After a normal G6PD test result, the patient was placed on primaquine for 14 days.

Epidemiologic Investigation

The two patients had no risk factors for malaria, including international travel, blood transfusion, organ transplantation, or needle sharing. The patients lived approximately 0.5 miles apart; however, the 19-year-old patient reported numerous visits to friends who lived directly across the street from the 15-year-old patient. Residents in the neighborhood surrounding the patients' homes were asked about recent febrile illnesses. Medical records from two hospitals serving residents in the patients' neighborhood also were reviewed, and charts of patients with a diagnosis of fever of unknown origin were obtained. None of the patients' neighbors had unexplained febrile illnesses. Of 224 hospital records available for review, 21 documented fever with no underlying cause. One of the 21 patients had persistent symptoms; however, a malaria smear did not reveal malaria parasites. No further cases of locally acquired malaria have been reported in northern Virginia.

Washington Dulles International Airport is located <10 miles from the patients' homes. The airport receives nonstop international flights from countries in which P. vivax malaria is endemic. Ill travelers are sent to one of the hospitals included in the investigation's case-detection activities. Physicians at two Army bases located nearby were contacted and reported no known cases of malaria or fever of unknown origin in troops returning from areas in which malaria is endemic.

Environmental and Entomologic Investigation

The patients' homes were visited. One home had several unscreened or poorly screened windows; the other had well-screened windows and a porch. Within the vicinity of both homes was a wooded area with a creek and ponds. As a part of ongoing West Nile virus (WNV) surveillance activities, trapping for anopheline mosquitoes within 10 miles of the patients' homes yielded Anopheles quadrimaculatus and An. punctipennis (Figure). Of approximately 870 anopheline mosquitoes tested, five pools (four to six mosquitoes per pool) captured within 2--6 miles of the patients' homes tested positive for P. vivax-210 circumsporozoite protein by using a field test (VecTest [Medical Analysis Systems, Inc., Camarillo, California]) on September 25 and 27 and October 1, 6, and 11. No mosquito pool has tested positive repeatedly in confirmatory testing by using polymerase chain reaction (PCR); however, efforts to confirm the positive VecTest mosquito pools are ongoing.

Reported by: A Pastor, MD, Loudoun Healthcare Dept of Infectious Diseases; J Neely, Clarke Environmental Mosquito Management; D Goodfriend, MD, Loudoun County Dept of Health, Leesburg; J Marr, MD, S Jenkins, VMD, D Woolard, PhD, D Pettit, PhD, D Gaines, PhD, D Sockwell, MSPH, Virginia Dept of Health. C Garvey, MD, C Jordan, C Lacey, Montgomery County Health Svcs, Rockville; T DuVernoy, DVM, Maryland Dept of Health and Mental Hygiene. D Roberts, PhD, L Robert, PhD, P Santos, Div of Tropical Public Health, Uniformed Svcs, Univ of the Health Sciences, Bethesda, Maryland. R Wirtz, PhD, J MacArthur, MD, Div of Parasitic Diseases; M O'Brien, Div of Applied Public Health Training, Epidemiology Program Office; L Causer, MBBS, EIS Officer, CDC.

Editorial Note:

Despite malaria eradication certification in the United States in 1970 (4,5), 10 outbreaks involving 17 cases of probable locally acquired mosquito-borne malaria transmission have occurred since 1992 (1). The two cases from northern Virginia represent the first cases of probable mosquito-borne malaria transmission in the United States since 1999 (1,2) and the second reported outbreak in Virginia (3). These outbreaks share common features: 1) an initial case without known risk factors for malaria, 2) probable proximity to a person with malaria parasitemia, 3) presence of competent mosquito vectors, and 4) environmental conditions conducive to the maturation of the parasite in the mosquito.

Approximately 1,000--1,500 cases of malaria in the United States are reported annually to CDC (6). The majority are diagnosed in travelers from countries in which malaria is endemic. The source of infection in the two northern Virginia residents was probably the bite of an infective mosquito that had acquired the parasite by biting a malaria-infected person in the general vicinity. Several Anopheles sp. mosquitoes native to the United States are competent malaria vectors. The An. quadrimaculatus and An. punctipennis mosquitoes captured near the patients' homes have been implicated in previous cases of locally acquired malaria (2,3). Numerous pools of these vectors were tested by using VecTest. Although this test is used commonly in international settings (7), this is the first time the test has been used in an investigation of mosquito-borne malaria in the United States. The identification of five malaria-positive pools among approximately 870 tested mosquitoes is unexpectedly high and has not been observed previously during an investigation of a malaria outbreak in the United States. Rapid screening tests such as the VecTest were not available previously. However, because VecTest is a new tool for the investigation of local mosquito-borne malaria in the United States, its validity in this setting is unknown, and results need to be confirmed by using PCR. Efforts are under way to develop testing algorithms for screening mosquito pools by using VecTest and confirming results with PCR.

This investigation underscores the need for clinicians to consider the possibility of malaria in patients with fever of unknown origin. Although a thorough travel history and risk-factor assessment should be a part of the evaluation of febrile patients, the possibility of malaria in patients without international travel, blood transfusion, organ transplantation, or needle sharing should be considered. Rapid diagnosis and treatment with effective antimalarial drugs are the basis of patient case management and will reduce the chances that an infected host will transmit the parasite. The same precautions recommended for minimizing exposure to WNV should be followed for reducing exposure to malaria-infected Anopheles sp. mosquitoes, including wearing long-sleeved shirts and long trousers, using insect repellent containing N,N-diethylm-toluamide (DEET), and avoiding outdoor activities during the late evening. Prompt reporting of patients with malaria to local public health authorities assists in activating control measures for these isolated cases of mosquito-borne malaria.


This report is based on data contributed by L Frank, R Helfrich, Montgomery County Health Svcs, Rockville; C Lesser, Maryland Dept of Agriculture; D Blythe, MD, Maryland Dept of Health and Mental Hygiene.


  1. MacArthur JR, Holtz TH, Jenkins J, et al. Probable locally acquired mosquito-transmitted malaria in Georgia, 1999. Clin Infect Dis 2001;32:E124--E128.
  2. CDC. Probable locally acquired mosquito-transmitted Plasmodium vivax infection---Suffolk County, New York, 1999. MMWR 2000;49:495--8.
  3. Strickman D, Gaffigan T, Wirtz RA, et al. Mosquito collections following local transmission of Plasmodium falciparum malaria in Westmoreland County, Virginia. J Am Mosq Control Assoc 2000;16:219--22.
  4. Bradley G. A review of malaria control and eradication in the United States. Mosquito News 1966;26:462--70.
  6. Wernsdorfer WH, McGregor I. Malaria: Principles and Practice of Malariology. Edinburgh, New York: Churchill Livingstone, 1988.
  7. Causer LM, Newman RD, Barber AM, et al. Malaria surveillance---United States, 2000. In: CDC surveillance summaries (July 12). MMWR 2002;51(No. SS-5):9--23.
  8. Ryan JR, Dave K, Collins KM, et al. Extensive multiple test centre evaluation of the VecTest malaria antigen panel assay. Med Vet Entomol 2002;16:321--7.


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