Duration of residency in a non-endemic area and risk of severe malaria in African immigrants

Abstract

In malaria-endemic areas, adults very rarely succumb to severe malaria, suggesting that immunity to severe disease is life-long under conditions of repeated exposure. To what extent this protection persists in the absence of exposure remains to be established. The aim of this study was to assess whether duration of residency in a malaria-free country affects the risk for severe malaria in immigrants originating from sub-Saharan Africa. We conducted a retrospective chart review of 948 cases of malaria diagnosed in Stockholm, Sweden in 1995-2013. Among 501 adult patients with Plasmodium falciparum (315 of endemic origin and 186 of non-endemic origin, mainly Sweden), 41 (8.2%) had severe malaria according to WHO criteria (including 5% with parasitaemia), 22 (4.4%) had factors prognostic of poor outcome, and 35 (7.0%) were admitted to intensive care. Overall, patient origin did not affect the odds of severe malaria, according to any of these definitions. However, when the immigrants were stratified with regard to their duration of residency in Sweden, the risk of factors prognostic for poor outcome was associated with duration of prior residency in a malaria-free country among patients of endemic origin (p 0.02), and immigrants who had lived for ≥ 15 years in Sweden had a similar risk as non-immune travellers. The results of this explorative study suggest that, although immunity to severe malaria is maintained for several years in African adults, this protection might be lost with time without repeated re-exposure. A larger study, preferably including multiple centres, will be needed to confirm our findings.

Sickle cell disease and malaria: decreased exposure and asplenia can modulate the risk from Plasmodium falciparum

“…As for acquired factors, partial immunity against malaria is usually acquired during the first 5 years of life, is dependent on the intensity of transmission and, therefore, on exposure frequency [19], and it tends to wane off with time if re-exposure does not occur [19,20].…”

“…A previous study has found that immigrants of African origin who had lived in Sweden (a malaria-free country) for 15 years or more, once they returned to Africa had a risk of malaria infection and of severe malaria similar to that of non-African travellers [20]. In the defense against malaria a significant role is played by the spleen because, by virtue of its unique anatomy, it can retain parasitized erythrocytes (as well as non-parasitized, but otherwise abnormal erythrocytes); indeed, impaired splenic function reduces the clearance rate of malaria parasites from the circulation [8,10,11].…”

Assessment of parasite clearance following treatment of severe malaria with intravenous artesunate in Ugandan children enrolled in a randomized controlled clinical trial

“…Time to clear parasites was significantly shorter compared to that proposed as indicator for artemisinin resistance. Artemisinin resistance is suspected to occur when > 10% of patients treated with ACT or artesunate monotherapy have positive parasitaemia on day 3 or a clearance half-life of ≥ 5 h [ 9 – 11 ]. These findings are consistent with reports from studies performed in some Asian countries including Bangladesh and Laos [ 15 ], as well as some African countries including Nigeria, Democratic Republic of Congo and Kenya which reported rapid parasite clearance times but differ from studies performed in Thailand and Cambodia where longer parasite clearance times and much higher proportions of patients with parasitaemia on day 3 were demonstrated [ 16 ].…”

“…Artemisinin resistance is suspected when > 10% of patients treated with artemisinin-based combination therapy (ACT) or artesunate monotherapy have positive parasitaemia on day 3 or ≥ 10% of patients have parasites with a clearance half-life ≥ 5 h. Resistance to artemisinins is confirmed when parasites persist in the blood for 7 days or with presence of parasites at day 3 and recrudescence within 28 days after treatment with oral artemisinin based monotherapy. Presence of > 5% of patients carrying K13 resistance-confirmed mutations confirms artemisinin resistance [ 9 – 11 ]. Some authors indicate a more sensitive threshold of > 5% day 3 parasite positivity to trigger further investigation for artemisinin susceptibility [ 12 ].…”

The Investigation of Malaria Cases in a Central Laboratory in İstanbul Region for a Period of Fifteen Years

“…Hem hasta ile ilgili hem de sağlık uygulamaları ile ilgili çeşitli faktörler tanı ve tedavide gecikmelere neden olabilmektedir. Bu faktörler arasında sıtmaya karşı değişen oranlarda immünolojik profiller sergilenmesi kemoproflaksi kullanılıp kullanılmadığı, sıtma olgularının nadir görülmesi ve özgül olmayan semptomlar ile ortaya çıkışı yer almaktadır (7)(8)(9). Bu nedenle bu olguların sıklığının ve özelliklerinin literatür verisi olarak ortaya konulması farkındalık oluşturarak, hayatı tehdit eden bir hastalık olmasının yanı sıra tedavi edilebilir olan hastalığın erken tanısına ve doğru tedavi uygulamalarına katkı sağlayacaktır.…”