Malaria Control During Mass Population Movements and Natural Disasters (2003)

Many currently nonmalarious areas have mosquito species that are competent malaria vectors, and the introduction of a large population of gametocytemic individuals can cause the introduction or reintroduction of malaria (Slutsker et al., 1995; Bawden et al., 1995). Major population movements can dramatically alter the local epidemiology of malaria in endemic areas (Kazmi and Pandit, 2001). Additionally, population movement has also been identified as a major cause for the spread of drug-resistant malaria into new geographical areas (Teklehaimanot, 1986; Dar et al., 1993). Returning or relocated populations can place a large burden on the health care infrastructure of the receiving location and, if the receiving location is not malarious, existing provisions for dealing with large numbers of malaria patients may be inadequate (Paxton et al., 1996).

Therefore, plans for the resettlement or repatriation of displaced populations should be evaluated for the potential for introduction or reintroduction of malaria or multidrug-resistant malaria into the receiving area, and strategies to limit the movement of parasites along with relocating human populations should be considered. Options include the following:

• Mass screening and selective treatment: All relocating individuals should be screened with an appropriate diagnostic test (typically thick blood films), and those who are positive should be treated with an effective antimalarial drug (including antirelapse or gametocytocidal agents, if indicated). However, individuals with subpatent infections or those with

P. vivax or P. ovale hypnozoites would not be identified and could become ill or act as a source of spread after relocation. Therefore, the capacity to diagnose and treat later would need to remain in place. This approach was recently used successfully for approximately 900 Vietnamese Montangard refugees being relocated from camps in Cambodia to the United States (Centers for Disease Control and Prevention, unpublished data). Because of an expected low prevalence of malaria in this population and limited treatment options due to drug resistance patterns in the region, all refugees were screened during routine pre-departure health screening with rapid diagnostic tests (with thick blood smears obtained as back-up). Only those proven to be positive were treated with a combination of mefloquine and artesunate. Because exposure to P. vivax was expected to be common, however, the entire population was treated presumptively with 14 days of primaquine (after being screened for G6PD deficiency) after arrival in the United States.

• Mass presumptive treatment: Everyone in a population should be treated presumptively with an effective antimalarial (including antirelapse agents if indicated). This option may be appropriate if the prevalence of malaria infection in the relocating population is high (Paxton et al., 1996; Centers for Disease Control and Prevention, 1998). Treatment should be done as close to the time of departure as possible to avoid the chance of reinfection before transit.

• Fever surveillance and case management: Surveillance (active or passive, as required) should be set up in the receiving area to identify individuals with febrile illness. These individuals should be diagnosed and treated with an effective antimalarial as needed. This option may be most appropriate among populations where initial malaria prevalence is very low, postrelocation surveillance is possible, and facilities capable of diagnosing and treating malaria are readily accessible. This might also be the least attractive option for populations with a high level of acquired malaria immunity. (Relatively few infections would be associated with fever and would therefore not be picked up by fever surveillance.)

Decisions regarding which option is the most cost effective must take into account a number of factors, including the prevalence of malaria in the displaced population; the level of asymptomatic infection; the risk of introduced malaria in the receiving area; the cost, efficacy, safety, and ease of use of the chosen malaria treatment; and the cost of diagnosing and treating malaria in the receiving area. These variables differ greatly from situation

to situation. For example, partly because of the very high cost of malaria treatment in the United States, the prevalence threshold for making mass treatment prior to relocation a more cost-effective approach for refugees being relocated from East Africa to the United States was as low as 2 percent (Cookson, 1999).

Another situation requiring planning is when displaced populations return to an endemic area after residing in a nonendemic area of refuge. Even after a relatively short period of time unexposed, acquired immunity can be diminished and, as a result, returnees can be at increased risk of severe illness and death. Adequate preparations should be made prior to arrival to educate returnees about the risks, to offer guidance and advice about the use of personal protection measures, to distribute insecticide-impregnated bed nets (if appropriate), and to provide effective antimalarial treatment to anyone exhibiting an illness suggestive of malaria.

• Consider interventions to address malaria, including curative and preventive services, at the point of departure or arrival. Responsibility for the provision of effective malaria control does not end with repatriation or resettlement.