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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.

SUBMITTER: Balzan M

PROVIDER: S-EPMC7375308 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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

Balzan Martin M

Medical hypotheses 20200722

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 opin ...[more]

PMID: 32759006

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Project description:BACKGROUND: In northern Europe, the tick-borne encephalitis virus (TBEV) of the European subtype is usually transmitted to humans by the common tick Ixodes ricinus. The aims of the present study are (i) to obtain up-to-date information on the TBEV prevalence in host-seeking I. ricinus in southern and central Sweden; (ii) to compile and review all relevant published records on the prevalence of TBEV in ticks in northern Europe; and (iii) to analyse and try to explain how the TBE virus can be maintained in natural foci despite an apparently low TBEV infection prevalence in the vector population. METHODS: To estimate the mean minimum infection rate (MIR) of TBEV in I. ricinus in northern Europe (i.e. Denmark, Norway, Sweden and Finland) we reviewed all published TBEV prevalence data for host-seeking I. ricinus collected during 1958-2011. Moreover, we collected 2,074 nymphs and 906 adults of I. ricinus from 29 localities in Sweden during 2008. These ticks were screened for TBEV by RT-PCR. RESULTS: The MIR for TBEV in nymphal and adult I. ricinus was 0.28% for northern Europe and 0.23% for southern Sweden. The infection prevalence of TBEV was significantly lower in nymphs (0.10%) than in adult ticks (0.55%). At a well-known TBEV-endemic locality, Torö island south-east of Stockholm, the TBEV prevalence (MIR) was 0.51% in nymphs and 4.48% in adults of I. ricinus. CONCLUSIONS: If the ratio of nymphs to adult ticks in the TBEV-analysed sample differs from that in the I. ricinus population in the field, the MIR obtained will not necessarily reflect the TBEV prevalence in the field. The relatively low TBEV prevalence in the potential vector population recorded in most studies may partly be due to: (i) inclusion of uninfected ticks from the 'uninfected areas' surrounding the TBEV endemic foci; (ii) inclusion of an unrepresentative, too large proportion of immature ticks, compared to adult ticks, in the analysed tick pools; and (iii) shortcomings in the laboratory techniques used to detect the virus that may be present in a very low concentration or undetectable state in ticks which have not recently fed.

Project description:BackgroundGovernments across the globe responded with different strategies to the COVID-19 pandemic. While some countries adopted measures, which have been perceived controversial, others pursued a strategy aiming for herd immunity. The latter is even more controversial and has been called unethical by the WHO Director-General. Inevitably, without proper control measures, viral diversity increases and multiple infectious exposures become common, when the pandemic reaches its maximum. This harbors not only a potential threat overseen by simplified theoretical arguments in support of herd immunity, but also deserves attention when assessing response measures to increasing numbers of infection.Methods and findingsWe extend the simulation model underlying the pandemic preparedness web interface CovidSim 1.1 (http://covidsim.eu/) to study the hypothetical effect of increased morbidity and mortality due to 'multi-infections', either acquired at by successive infective contacts during the course of one infection or by a single infective contact with a multi-infected individual. The simulations are adjusted to reflect roughly the situation in the USA. We assume a phase of general contact reduction ("lockdown") at the beginning of the epidemic and additional case-isolation measures. We study the hypothetical effects of varying enhancements in morbidity and mortality, different likelihoods of multi-infected individuals to spread multi-infections and different susceptibility to multi-infections in different disease phases. It is demonstrated that multi-infections lead to a slight reduction in the number of infections, as these are more likely to get isolated due to their higher morbidity. However, the latter substantially increases the number of deaths. Furthermore, simulations indicate that a potential second lockdown can substantially decrease the epidemic peak, the number of multi-infections and deaths.ConclusionsEnhanced morbidity and mortality due to multiple disease exposure is a potential threat in the COVID-19 pandemic that deserves more attention. Particularly it underlines another facet questioning disease management strategies aiming for herd immunity.

Dataset Information

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

Publications

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

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