Malaria in travellers and migrants

Abstract

Malaria is a potentially fatal disease that caused approximately 241 million cases and 627 000 deaths in 2020, most in children in Sub-Saharan Africa. In non-endemic countries, malaria is imported by travellers and migrants and timely management and treatment is crucial. Since mild episodes can progress to severe malaria with vital organ failure it is important to identify patients at high risk. Severe malaria is defined by the World Health Organization (WHO) and intravenous treatment is recommended for patients fulfilling any of the criteria for severity. It is, however, not clear if these criteria and recommendations are optimal in non-endemic countries. Moreover, management of malaria in migrants may also need to consider persistent low-density infections with no or discrete symptoms that may have negative health effects. The aim of this thesis was to contribute to improved identification, treatment, and management of malaria in travellers and migrants

In Study I, we describe the epidemiology and severity of imported malaria in travellers and migrants in a nationwide study in Sweden (n=2653). In P. falciparum, young and older age, patient origin in a non-endemic country, health care delay, pregnancy and HIV-infection were identified risk factors for severe disease. Oral treatment of P. falciparum episodes with parasitemia >2% increased the risk of progression to severe malaria. In P. vivax, a high proportion of severe malaria was seen in newly arrived migrants.

In Study II, we studied relapses of P. vivax and P. ovale after treatment in a non-endemic setting. The risk of relapse was substantially higher for P. vivax compared to P. ovale. Primaquine significantly reduced the risk of relapse in P. vivax, however, in P. ovale, relapses were rare and the effect of primaquine was less evident.

In Study III, we assessed how the WHO criteria for severe malaria reflect disease severity in terms of death or need of prolonged intensive care in adults in a non-endemic setting. Overall, the WHO criteria had high sensitivity and specificity for the unfavourable outcome also compared to other scoring systems. The predicting ability was improved when using only three criteria: cerebral impairment (GCS ≤14 or multiple convulsions), ≥2.5% P. falciparum parasitemia or respiratory distress (respiratory rate >30/min, or acidotic breathing).

In Study IV, the prevalence of malaria parasites was assessed in migrants from Sub-Saharan Africa residing in Sweden. The overall asymptomatic parasite prevalence was 8%, by PCR. However, in migrants arriving from Uganda the prevalence was higher, and especially in children where over 30% were parasite positive by PCR, and often detected in family members. The longest duration of residency in Sweden at sampling among PCR positives was 386 days for P. falciparum.

In conclusion, severe malaria occurred in all species and patients at high risk for severe outcome can be identified with new simple criteria and should be recommended intravenous treatment. Screening for malaria parasites should be considered as part of the health screening offered to migrants.