THE PARASITE Plasmodium vivax is responsible for the majority of malaria cases outside of sub-Saharan Africa, and research conducted at Harvard T.H. Chan School of Public Health, Boston, Massachusetts, USA focussing on the parasite’s lifecycle has identified that P. vivax is found not only in the blood but also in the bone marrow. This key finding may enhance the detection and treatment of many other blood-borne diseases.
P. vivax was once thought to cause a ‘benign’ malaria because the infection is often asymptomatic and results in far fewer deaths than Plasmodium falciparum, which causes 90% of malaria deaths across the globe. However, it is now understood that tens of millions of people, particularly in South America and south east Asia, are affected by P. vivax every year, contributing to a large healthcare burden.
By firstly investigating the transcriptome of P. vivax to find lifecycle-related blood-borne proteins, and then analysing patient blood samples for these protein biomarkers, the researchers revealed that proteins corresponding to the major stages of the lifecycle were underrepresented in the blood, which suggested a parasite store in another tissue or organ of the body. Tissues such as bone marrow, lung, liver, brain, intestine, and subcutaneous fat from 13 infected non-human primates were investigated in an attempt to find the reservoir for parasite replication. Bone marrow was suspected as the P. vivax store from an early stage due to the parasite’s propensity to attack young erythrocytes, and, as hypothesised, the research team found parasites that had left the blood stream in both the bone marrow and liver tissues. It was estimated that these tissues comprised 30% of the total parasite burden.
The researchers hope that the biomarkers used and the identification of this previously unknown pool of P. vivax will usher in a new age of malaria therapeutics and diagnostic tools to combat a haematological disease that affects a large proportion of the planet’s population.