Genetically modified mosquitos may be used in fight against Zika

In the interesting “News article” by Anne Gulland,[1] reference is made to the possibility of employing, as a biological “weapon” against Zika virus (ZIKV), male Aedes aegypti mosquitoes carrying Wolbachia, a Gram-negative bacterial agent infecting only invertebrates, with the plausible and desirable expectations of a reduction in moquitoes’ lifespan as well as in the viral loads potentially transmissible by ZIKV-infected mosquitoes to humans.

In this respect, concern has recently been drawn about the possibility that, alongside with A. aegypti, other mosquitoes such as A. albopictus could become efficient ZIKV vectors.[2] A similar “scenario” would likely be even more detrimental, given that A. albopictus is far more common than A. aegypti in the Northern and in the Western Hemisphere, with 32 among the 50 States from USA having detected its presence.[2] It is also worth mentioning that A. albopictus has been identified as an efficient vector for Dirofilaria immitis, a cardio-pulmonary nematode of dogs and cats [3] which may be infected, in its turn, by Wolbachia. An inflammatory response elicited by Wolbachia is known to develop in D. immitis-affected dogs and cats,[4], so that it would be important to investigate "whether and how" interfering with, or by means of, Wolbachia, in the ecology, epidemiology and evolution of given arthropode-borne infections could affect not only the "insect vector" but also the "organism" carried inside it, be it a virus or a nematode (as in the case of D. immitis).

Indeed, antimicrobial therapy against Wolbachia has resulted in decreased microfilarial loads, inhibition of the development of larval worms, female worm infertility and reduced numbers of Wolbachia organisms.[4] Consequently, at least in the canine and feline D. immitis, arthropod-borne infection model, the presence and the number of Wolbachia organisms appear to get along very well with a "canonical" development and progression of the disease process, quite differently therefore from what may be expected in ZIKV-infected, Wolbachia-challenged mosquitoes.[1].

In the light of what above, this appears to be an extremely delicate "equilibrium", made up by 4 different and mutually interacting "variables", namely the "pathogen", the "insect", the "host" and the "environment", with the additional possibility that the "interaction patterns" of the pathogen and Wolbachia may substantially diverge from those occurring between Wolbachia and the agent's mosquito vector.

In conclusion, the aforementioned issues and concerns would deserve adequate consideration and ad hoc study efforts.

Giovanni DI GUARDO, DVM, Dipl. ECVP,
University of Teramo, Faculty of Veterinary Medicine, Località Piano d'Accio, 64100 - Teramo, Italy; e-mail address: gdiguardo@unite.it

Conflict of interest statement
The author declares that no conflicts of interest of any kind exist in relation to the publication of this manuscript.

References

1 Gulland A. Genetically modified mosquitos may be used in fight against Zika. BMJ 2016;352:i1086 doi: 10.1136/bmj.i1086 (Published 22 February 2016).

2 Fauci AS, Morens DM. Zika virus in the Americas - Yet another arbovirus threat. N Engl J Med 2016;doi: 10.1056/nejmp1600297 (Published 13 January 2016).

3 Morchón R, Carretón E, González-Miguel J, et al. Heartworm disease (Dirofilaria immitis) and their vectors in Europe - New distribution trends. Front Physiol 2012;3:196 doi: 10.3389/fphys.2012.00196.

4 Frank K, Heald RD. The emerging role of Wolbachia species in heartworm disease. Compend Contin Educ Vet 2010;32(4):E4.