Low Incidence and Mortality from SARS-CoV-2 in Southern Europe. Proposal of a hypothesis for Arthropod borne Herd immunity

Abstract

SARS-CoV-2 incidence and mortality in Europe have shown wide variation. Northern Italy in particular the Lombardy region, north-eastern French regions, Switzerland and Belgium were amongst the hardest hit, while the central and southern Italian regions, all the Balkan countries from Slovenia to Greece and the Islands of Malta and Cyprus had much fewer cases and deaths per capita, and deaths per number of cases. Differences in public health measures, and health care delivery, in the author’s opinion, can only partly explain the difference. The geographical distribution of Phlebotomus sand-flies and the relative distribution of arthropod borne diseases Leishmaniasis and Phlebovirus infections especially the Sicilian Sandfly fever group corresponds to most areas of low prevalence of SARS-CoV-2. A hypothesis is proposed whereby repeated arthropod or sandfly vector infection of humans by novel viruses of zoonotic origins carrying bat or mammalian RNA/DNA, such as phleboviruses may have resulted in the development of an effective evolutionary immune response to most novel zoonotic viruses such as SARS-CoV-2 by means of survival of the fittest possibly over many generations. This process probably ran in parallel and concurrent with the progressive evolution of novel coronaviruses which spread from one mammalian species to another. Other possible, but less likely mechanisms for the role of sandfly meals within a much shorter time frame may have led to, (i) previous exposure and infection of humans with the SARS-Cov-2 virus itself, or a closely related corona virus in the previous decades, or (ii) exposure of human populations to parts coronavirus protein namely either S or more likely N protein carried mechanically by arthropods, but without clinical disease causing direct immunity or (iii) by causing infection with other arthropod borne viruses which could carry bat DNA/RNA and have similar functional proteins resulting in an immediate cross-reactive immune response rather than by natural selection. The Evidence possibly supporting or disputing this hypothesis is reviewed, however the major problem with the hypothesis is that to date no coronavirus has ever been isolated from arthropods. Such a hypothesis can only be supported by research investigating the possible biological relationship of arthropods and coronaviruses where paradoxically they may be promoting immunity rather than disease.

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“…As stated in the original paper, the incidence of Sars-Covid-2 infection could reflect the effectiveness of public health measures and the capacity of the health care system to cope with the number of sick people during the epidemic as well as for the deployment of testing [1]. Analysis of geographic data provided for example by ECDC is not age-stratified and might be subject to errors of over or underrepresentation of specific age groups, or vulnerable population subgroups.…”

“…Low prevalence of Mortality and case fatality rates to Sars-Covid-2 were noted in many areas of southern Europe particularly in areas where phlebotomous sandflies and phlebovirus infections are prevalent [1]. Phleboviruses carry bat, artiodactyl, and rodent RNA showing an ability to mutate and evolve across mammalian species, in a way similar to human coronaviruses [2].…”

“…Phleboviruses carry bat, artiodactyl, and rodent RNA showing an ability to mutate and evolve across mammalian species, in a way similar to human coronaviruses [2]. A possible hypothesis was proposed by this author that by a process of natural selection after exposure of such novel viruses over many generations it is possible that the innate immune system could be more protective against novel viruses such as Sars-Covid-2 [1].…”