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ASTMH Meeting Highlights 2010
Abstract & Commentary
By Lin H. Chen, MD
Dr. Chen is Assistant Clinical Professor, Harvard Medical School; Director, Travel Medicine Center, Mt. Auburn Hospital, Cambridge MA
Dr. Chen has received research grants from the Centers for Disease Control and Prevention and Xcellerex.
At the 59th annual meeting of the american society of Tropical Medicine and Hygiene held in Atlanta, GA, Nov. 3-7, 2011 (see abstracts, below), Dr. Paul Arguin, head of the Domestic Malaria Unit, presented Malaria Updates from the Centers for Disease Control and Prevention (CDC). For 2009, 1,490 cases of malaria were reported to the CDC. The most commonly reported reason for travel was visiting friends and relatives (61.7%), followed by missionary (9.5%), business (5.8%), and tourism (4.7%). The top exposure countries for all reported cases of malaria in the United States in 2009 were Nigeria, Ghana, India, Haiti, Sierra Leone, and Ivory Coast. The most common exposure countries for U.S. residents included the same countries.
The reported malaria cases most frequently had exposure in West Africa (51.4%), as illustrated by the Nov. 5, 2010, issue of Morbidity and Mortality Weekly Report, which described four cases of Plasmodium falciparum in flight crew acquired in Accra, Ghana.1 These cases showed the continued high transmission of malaria in west Africa even for brief stays, and emphasize the importance of mosquito avoidance measures as well as malaria chemoprophylaxis.
Malaria in Haiti has been a concern. Prior to the earthquake in 2009, the CDC received 59 reports of malaria acquired in Haiti, compared to 19 cases in 2008. For 2010, there have already been 35 cases reported, including eight severe cases.
Dr. Arguin reported some notable changes in malaria prevention guidelines because no malaria transmission has occurred in Iguassu Falls, Angkor Wat, Armenia, Bahamas, Syria, and Turkmenistan. Additionally, mosquito avoidance only is recommended for travelers to Cape Verde, Iraq, Quintana Roo, and Tabasco in Mexico, and all areas except Limon Province in Costa Rica. He emphasized that the recommendation of chemoprophylaxis should not be based on geography alone, but also requires individual risk assessment.
Dr. Gary Brunette, head of the Travelers' Health Branch, presented Travelers' Health Updates. Recent changes in vaccine recommendations include: 1) Ixiaro® is approved and available for persons age 17 and older to prevent Japanese encephalitis, whereas JE Vax® is only recommended now for persons age 1-16 years; 2) a four-dose rabies post-exposure prophylaxis is recommended in persons without pre-exposure prophylaxis and includes rabies immune globulin plus rabies vaccines given on days 0, 3, 7, 14 for normal hosts, but a fifth dose should be given on day 28 to immune-suppressed hosts; and 3) additional yellow fever vaccine precautions include age ≥ 60 years and HIV-positivity with CD4 of 200-499.
The Yellow Fever (YF) Vaccine Working Group formed by the World Health Organization, Centers for Disease Control and Prevention, National Travel Health Network and Centre, and other experts are continuing to harmonize yellow fever country risks and vaccine recommendations. The new YF risk classification criteria will be stratified to four groups: endemic, transitional, low, and no risk; the risk maps will correspond to vaccination maps. The following countries in the African region will probably have changes in YF risk classification: Democratic Republic of the Congo, Eritrea, Ethiopia, Kenya, Sao Tome, and Principe, Somalia, Tanzania, Zambia. In the Americas, changes probably will occur for Argentina, Brazil, Colombia, Ecuador, Panama, Paraguay, Peru, Trinidad and Tobago, and Venezuela. Until the new recommendations are formalized and published, travel medicine providers are advised to follow the current guidelines.
Additionally, the CDC has produced a YF Vaccine Course in collaboration with experts. It is an online module, is free, and offers CME, CNE, CPE, and CHES credits. Access to the module is via the CDC Travelers' Health Website. Finally, the Yellow Book 2012 will be available in spring 2011.
[Acknowledgement: The Associate Editor thanks Drs. Paul Arguin and Gary Brunette for sharing their ASTMH presentations and for reviewing this report.]
A number of interesting studies were presented at the ASTMH annual meeting, including the following from the Clinical Tropical Medicine Scientific Session I.
Monath TP, et al. Inactivated, cell-based yellow fever 17d vaccine safety and immunogenicity in animal models and results of a phase 1 clinical trial.
An inactivated yellow fever vaccine has been developed using YF 17D RNA grown in Vero cells. Studies in mice, hamster, and monkeys have shown that a single dose led to antibody titers similar to the live-attenuated YF vaccine (antibody ≥ 20) by day 21. A randomized, double-blind phase 1 clinical trial found that two doses given on days 0 and 21 were safe, and compared a low-dose to a high-dose regimen. On day 21, low-dose regimen achieved 12.5% seroconversion and high-dose achieved 45% seroconversion. By day 31 (10 days after the second dose), 100% of subjects achieved seroconversion.
Inactivated YF vaccine appears promising in a phase 1 clinical trial, and we await results of additional trials.
D'Acremont V, et al. Etiology of fever in children from urban and rural Tanzania.
The investigators analyzed 1,005 children age 2 months to 10 years (median, 18 months) with temperatures > 38º C, collected clinical information and test results, and derived levels of probability for the diagnoses. The children were recruited from Dar Es Salaam (n = 507) and Ifakara (n = 498). Acute respiratory infections (ARIs) accounted for 50%, malaria 10%, GI infections 9%, typhoid fever 3%. Among the
ARIs, one-quarter were influenza, and both arenavirus and picornavirus also were prevalent. Those with unknown diagnoses were tested by PCR; dengue, chikungunya, Rift Valley fever, and West Nile fever were ruled out, but a high rate of HHV6 infection was detected. Acute respiratory infections appear to be the most common cause of fevers among children in two Tanzanian communities. Malaria, GI infections, and typhoid also were identified. When evaluating febrile illnesses in children, clinicians working in similar communities should direct specific diagnostic testing to identify these common etiologies.
William T, et al. A retrospective study of severe Plasmodium knowlesi infections at Queen Elizabeth Hospital, Sabah, Malaysia.
The investigators retrospectively reviewed clinical records of patients who were diagnosed with P. knowlesi at Queen Elizabeth Hospital, a tertiary referral center in Kota Kinabalu, Sabah, Malaysia. P. knowlesi accounted for 24% of all cases of malaria at QEH (78/324), and 34% of P. knowlesi cases had severe disease. The patients commonly had hematological abnormalities and hyperbilirubinemia, especially older individuals. Other studies including dengue virus were all negative. A high proportion had severe malaria, including 64% with respiratory distress and 59% with acute renal failure. Among 23 patients with severe disease, five died (22%). ACT is effective for treatment.
This series shows that P. knowlesi can cause severe disease and is a major cause of severe malaria at QEH. Travel medicine providers should be aware of this recently identified strain of Plasmodium and evaluate febrile travelers appropriately.