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Imunidade à malária em imigrantes de países endémicos
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Em áreas endémicas com alta transmissão de malária as populações desenvolvem imunidade natural à doença. Em países não endémicos, a malária é uma doença importada por viajantes. Crescentes comunidades de imigrantes de áreas endémicas que viajam para visitar amigos e familiares (VFR) constituem agora a maioria dos viajantes para destinos endémicos. Existem visões contraditórias sobre a suscetibilidade destes viajantes à doença. Assim, foi realizada uma revisão da literatura sobre imunidade natural à malária em populações endémicas e epidemiologia da malária importada em países não endémicos.
A imunidade é adquirida apenas em contexto de alta transmissão e depende da exposição e da idade. A imunidade clínica a doença grave é adquirida precocemente em crianças por meio de mecanismos anti-doença. A capacidade de controlar a parasitemia (imunidade anti-parasita), amplamente dependente de anticorpos contra a fase eritrocítica da infeção, protege os adultos de infeção sintomática, permanecendo suscetíveis a parasitemia assintomática. Na ausência de exposição mantida, a imunidade é parcialmente perdida e os indivíduos tornam-se suscetíveis a reinfeção sintomática, como acontece com os imigrantes VFR. Estes indivíduos viajam por períodos mais longos para ambientes de alto risco e têm pior adesão a profilaxia, apresentando maior risco de infeção que os outros viajantes. No entanto, embora doença grave e morte possam ocorrer, são significativamente menos frequentes, indicando a persistência de algum grau de proteção em pelo menos alguns desses imigrantes.
Investigação futura deve procurar fatores protetores entre diferentes imigrantes para tentar identificar subgrupos mais protegidos. O desenvolvimento de biomarcadores robustos e assinaturas moleculares de imunidade também poderá permitir uma avaliação personalizada do risco e recomendações de profilaxia.
Em conclusão, apesar de terem menor risco de gravidade e morte enquanto grupo, os imigrantes de áreas endémicas não podem ser considerados imunes, e medidas preventivas, incluindo quimioprofilaxia, devem ser recomendadas a estes viajantes tal como aos restantes.
It is well known that in endemic areas with high malaria transmission, people develop naturally acquired immunity to the disease. In non-endemic countries, malaria is a traveler-imported disease. Growing immigrant communities from endemic areas now make up a major portion of travelers to endemic destinations when travelling to visit friends and relatives (VFR). Conflicting views exist regarding susceptibility of these travelers to disease. This question was addressed through a review of literature on natural malaria immunity in endemic populations and epidemiological data on imported malaria cases. Immunity is acquired only in high transmission settings in an exposure and age-dependent manner. Clinical immunity to severe disease is firstly acquired in children through anti-disease mechanisms. The ability to control parasitemia (anti-parasite immunity), largely dependent on antibody responses to the erythrocytic stage of infection, protects adults from clinical malaria, while still rendering them susceptible to asymptomatic parasitemia. In the absence of maintained exposure, immunity is partially lost, and individuals become susceptible to disease when reinfected, as is the case with VFR immigrants. Additionally, VFRs travel for longer periods to high risk settings and adhere poorly to prophylaxis, rendering them at higher risk of infection. Nonetheless, while severe disease and death can occur in this group, they are significantly less frequent than in other travelers, indicating persistence of some degree of protection in at least some of these immigrants. Future research should focus on addressing protective factors among different immigrant travelers to attempt to identify protected subgroups. Developing robust biomarkers and molecular signatures of immunity which are absent would also allow for personalized assessment of risk and prophylaxis recommendations. Despite lower risk of severity and death as group, immigrant travelers cannot be considered immune, and preventive measures including chemoprophylaxis should be recommended to immigrant and non-immigrant travelers alike.
It is well known that in endemic areas with high malaria transmission, people develop naturally acquired immunity to the disease. In non-endemic countries, malaria is a traveler-imported disease. Growing immigrant communities from endemic areas now make up a major portion of travelers to endemic destinations when travelling to visit friends and relatives (VFR). Conflicting views exist regarding susceptibility of these travelers to disease. This question was addressed through a review of literature on natural malaria immunity in endemic populations and epidemiological data on imported malaria cases. Immunity is acquired only in high transmission settings in an exposure and age-dependent manner. Clinical immunity to severe disease is firstly acquired in children through anti-disease mechanisms. The ability to control parasitemia (anti-parasite immunity), largely dependent on antibody responses to the erythrocytic stage of infection, protects adults from clinical malaria, while still rendering them susceptible to asymptomatic parasitemia. In the absence of maintained exposure, immunity is partially lost, and individuals become susceptible to disease when reinfected, as is the case with VFR immigrants. Additionally, VFRs travel for longer periods to high risk settings and adhere poorly to prophylaxis, rendering them at higher risk of infection. Nonetheless, while severe disease and death can occur in this group, they are significantly less frequent than in other travelers, indicating persistence of some degree of protection in at least some of these immigrants. Future research should focus on addressing protective factors among different immigrant travelers to attempt to identify protected subgroups. Developing robust biomarkers and molecular signatures of immunity which are absent would also allow for personalized assessment of risk and prophylaxis recommendations. Despite lower risk of severity and death as group, immigrant travelers cannot be considered immune, and preventive measures including chemoprophylaxis should be recommended to immigrant and non-immigrant travelers alike.
Descrição
Trabalho Final do Curso de Mestrado Integrado em Medicina, Faculdade de Medicina, Universidade de Lisboa, 2021
Palavras-chave
Malária Imunidade natural adquirida Imigrantes Visitar amigos e familiares (VFR)