We talk about asymptomatic, submicroscopic plasmodial infections as potentially being a threat to the elimination of malaria. This is, of course, partly because such infections are not normally treated; especially not in rural endemic areas where laboratory facilities are limited. An aggravation of the situation is when parasitaemias are so low that they cannot be detected by molecular diagnosis (where available) either. But obstacles to elimination are probably even greater than has been realized.
This is because when no parasites are found in the bloodstream by any techniques (parasitaemia perhaps being controlled by immunity at the time), there might, with currently unknown frequency, nevertheless be plenty of merozoites concealed extravascularly in the bone marrow and elsewhere; and which could well be a source of recrudescences (subclinical or otherwise). This is a newly recognized life cycle phenomenon. Accordingly, we need to move away from thinking of malaria as being merely blood and liver-associated, parasitologically. In relation to the concept of malaria elimination, it is now time to give consideration to the broader, more complicated scenario referred to above. (Link to a September 2018 article that elucidates the problem [click here]).