Asymptomatic Infections by P. vivax Contribute to Sustaining Malaria Transmission

A team led by Dr. Ivo Mueller, researcher at ISGlobal and the Walter and Eliza Hall Institute in Melbourne, Australia, has been the first to apply sensitive molecular diagnosis tools to perform a large-scale epidemiological study of malaria in the Solomon Islands.    

As a result of scaled-up control interventions, the Solomon Islands has achieved an impressive 90% reduction in malaria incidence over the last twenty years, and is now aiming at elimination of the disease.  However, asymptomatic infections, that are normally undetectable by classical diagnosis tests based on light microscopy, can contribute to sustaining parasite transmission, even in areas with low density of infections. Therefore, the authors sought to determine the prevalence of asymptomatic infections of Plasmodium vivax and Plasmodium falciparum in a low transmission area of Salomon Islands, using sensitive molecular diagnosis. 

The results, published in Plos Neglected Tropical Diseases, show that P. vivax remains endemic, with a high prevalence of asymptomatic infections that are undetectable by microscopy. These silent infections however can produce gametocytes (the infectious phase of the parasite) and can thus contribute significantly to disease transmission. In contrast, P. falciparum has practically disappeared and the few detected cases are likely due to re-introductions by incoming travellers. 

These results represent a considerable challenge for the national malaria control programs based on classical Plasmodium detection tests. Accordingly, the authors conclude, disease elimination will require new strategies to detect and treat the reservoir of silent P. vivax infections.  

Reference:

Waltmann A et al. High Rates of Asymptomatic, Sub-microscopic Plasmodium vivax Infection and Disappearing Plasmodium falciparum Malaria in an Area of Low Transmission in Solomon Islands. PLoS Negl Trop Dis. 2015 May 21;9(5):e00037

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