Loiasis: The case of the Indian reports

I read with interest the article published in this journal by Simran et al. concerning the extraction of an (alleged) adult female Loa loa from the eye of an Indian woman.[1] Loiasis, as is well known, is a nematodiasis of the connective tissues endemic in some West-Central African countries, caused by the aforementioned filaria and transmitted to humans by diurnal haematophagous horseflies of the genus Chrysops. The prepatent period is typically long, so cases are sometimes reported in the nonendemic countries, where immigrant patients or tourists who contracted the infection in Africa show signs and symptoms months or even many years after transmission.[2] However, this case, as the patient denied travelling to an endemic area, fits the anecdotal pattern of reports of loiasis contracted in a nonendemic country, for which India holds the curious record. Unfortunately, even a first reading reveals inconsistencies and inaccuracies. The problem with this report - and others like it - Is not the presence or absence of potential L. loa vectors; the genus Chrysops does indeed have representatives outside Africa, and there are even some local Indian species eligible for the role. Instead, the issues lie in the incongruence between the length of the filaria extracted from the patient (105 mm) and the maximum length recorded for a female L. loa (70 mm).[3] These significant discrepancies, coupled with the complete lack of molecular confirmation, pose the greatest challenge to the credibility of all identifications in presumed indigenous Indian cases. Some authors justify the oversized measurements by suggesting the existence of an enigmatic “Indian” species or strain of the parasite. This misunderstanding originates from the work of the Australian physician Maplestone, who, in 1938, described the case of a woman in Mumbai from whom an adult female filaria was extracted from the eye.[4] Despite obvious morphological and size differences (the specimen was more than twice the length of L. loa), Maplestone wanted to attribute it to the genus Loa. Almost a century after Maplestone’s publication, no evidence has been found to support his theory and L. loa remains the only recognised species in the genus Loa. While we wait for molecular investigations to be carried out in some of the next cases, the most probable hypothesis regarding the etiology of this case, as well as many other similar ones, is that we are dealing with species already historically present in India and known for their possible ocular localisation. The examples include Wuchereria bancrofti, Brugia malayi, and Dirofilaria asiatica, or possibly even undescribed species belonging to these genera. Finally, in the interest of scientific rigor, we should also point out the errors made by the authors when reporting the names of the main vectors of L. loa: they refer to “Chrotomys silaceus,” a rodent endemic to the Philippines, and “Calopteryx dimidiata,” a damselfly endemic to the USA, instead of “Chrysops silacea” and “Chrysops dimidiata,” respectively. Data availability statement The data supporting the findings of this study will be made available upon reasonable request. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.