Entomology in the Time of COVID-19 – Part 2: Can mosquitoes spread SARS-CoV-2?

In Part 1 of this series, I posed the question: Can insects spread SARS-CoV-2? As I have mentioned there, that question is difficult to answer at present. First, SARS-CoV-2 is new to us. In fact, its original tentative name was nCoV, for novel coronavirus. Needless to say, science is still investigating all its angles, and fortunately, developments are relatively rapid particularly in the most urgent aspects. Second, there are no efforts yet on detecting and documenting the occurrence and viability of the virus particles on hosts other than humans, bats, and pangolins and on certain surfaces like plastics, fabric and metals. Most of the existing articles on the topic are speculative and largely leaning to enticement of clients to patronize pest control services. Under the present economic situation, pest control would be a good part of sanitation but could not be a priority for most people.

This attempt to give answers also aims to help lessen people’s worries so that they may concentrate on the more salient measures to help ‘flatten the curve.’ The answers here are tentative, but the good thing is, they are from the viewpoint of an entomologist – a person who studies insects. The bases of the answers given below are general knowledge on the biology of these insects, their known roles and behaviors in relation to spread of communicable diseases, and the available, albeit limited, data on incidence of the virus in clinical samples. These answers are also admittedly largely speculative but effort is made to provide statements of hypotheses. These hypotheses may be or, rather, need to be tested and supported with empirical evidence hopefully by a team – at least an entomologist, a medical epidemiologist, and a molecular biologist-virologist.

So let us see, the mosquitoes first

At least three species of mosquitoes, Aedes aegypti (L.), Aedes albopictus (Skuse), and Culex spp., are among blood-sucking insects known to be vectors of human disease-causing viruses. Aedes species are carriers of dengue, zika, and chikungungya viruses while Culex species are known to transmit Japanese encephalitis virus. The other well-known medically important mosquitoes are Anopheles spp., vectors of Plasmodium spp. that cause malaria, and various species that can carry filarial parasites.

For mosquito vectors to be able to spread viruses, the pathogen must be highly present in the host’s blood. The details of this will be discussed in Part 3 of this series. In the meantime, let us examine what is currently the known incidences of positive detection of SARS-CoV-2 in clinical samples as provided by Wang et al. (2020), thus:

Based on their data, only one percent of blood samples tested positive for the coronavirus. Although this indicates that the viral infection may be systemic, the low positivity rate for blood samples may also suggest, but not automatically, low possibility of transmission through the blood and by inference, low possibility of blood-sucking mosquitoes becoming vectors. However, this is still a hypotheses, and it requires confirmation with molecular evidence.

One of the dengue mosquitoes, Aedes albopictus – this one has just emerged from its pupa. Photo credits: Cristian C. Lucañas

Jun Lit (Ireneo L. Lit, Jr.)

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