What could be the reason that some Asian countries like Sri Lanka have less severe and more asymptomatic patients with reduced incidence of spread, compared to temperate countries?
Many factors contribute to lessening of severe diseases and spread in tropical countries. One important factor could be Previous Dengue infections, which may have some protection against Covid 19. Dengue and Coronavirus disease 2019 (COVID-19) are difficult to distinguish because they have shared clinical and laboratory features1.
Dengue is endemic in many Asian countries2 and populations have antibodies to dengue virus due to previous clinical or subclinical infections. Covid 19 virus and dengue virus have structural and antigenic similarities. Both are single stranded RNA viruses3. Dengue rapid IGM and IGG test have been positive in Covid 19 PCR positive patients in Singapore4 and also reported in Sri Lanka5.
This antigenic similarity can result in some protection against Covid 19 infections. This could be the reason why the people in dengue endemic countries like Sri Lanka have Asymptomatic and less severe infections.
It is important to study the previous history of Dengue infections and dengue antibodies in Covid 19 patients with relation to disease outcomes.
Another important factor could be the protective effects of TB vaccination, which is given at birth in many Asian countries6.
Strong sunlight with increased UV radiation high humidity and high ambient temperature will make the virus less viable in the environment. This could be the reason for reduced rate of infection in Asian countries compared to temperate countries.
Food habits and herbal remedies could be another important factor determining the severity of the disease because there is clear difference in type of food consumed by countries with severe disease and mild disease. Gluten containing food is consumed more in countries like Italy Spain England and America where the disease is severe when compared to Asian countries, which consume less gluten containing food. People in Asian countries consume more spices in food like turmeric, coriander, cinnamon and consume tea7 fervently all theses could have protective effects ageist Covid 19 infection.
Genetic factors, efficient contact tracing, early case detection and early treatment with Hydroxychloroquine are other factors that may be contributing to less sever infections.
All above deductions are on observations and proper design research is necessary to confirm the above conclusion.
References
- Chen N., Zhou M., Dong X. et al., (2020). Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study. 2020; vol395: Pg507-513. doi:10.1016/S0140-6736(20)30211-7. [Online] available at; <https://pubmed.ncbi.nlm.nih.gov/32007143/> [Accessed on 9 May 2020].
- World Health Organization., (2015). Dengue and Severe Dengue. int. [Online] available at; <http://www.who.int/mediacentre/factsheets/fs117/en/> [Accessed on 9 May 2020].
- Mousavizadeh L., Ghasemi S., (2020). Genotype and phenotype of COVID-19: Their roles in Pathogenesis., Journal of Microbiology, Immunology and Infection. doi:10.1016/j.jmii.2020.03.022. [Online] available at; <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7138183/> [Accessed on 9 May 2020].
- Yan G., Lee C.K., Lam L.T.M. et al., (2020). Covert COVID-19 and false-positive dengue serology in Singapore., The Lancet Infectious Diseases., 2020;vol20(5):Pg536. doi:10.1016/S1473-3099(20)30158-4. [Online] available at; <https://pubmed.ncbi.nlm.nih.gov/32145189/> [Accessed on 9 May 2020].
- Ada Derena 24 Big Focus | Sri Lanka's News Channel., (2020). කොරෝනා හැදුනු වෛද්යවරයාගේ කතාව මුල් වරට මාධ්ය හමුවට., [Online] available at; <https://m.youtube.com/watch?v=f72ZUA3QcII> [Accessed on 9 May 2020].
- Kylie Q., Joanna K., Katie L. et al., (2020). Could BCG, a 100-year-old vaccine for tuberculosis, protect against coronavirus? [Online] available at; <https://theconversation.com/could-bcg-a-100-year-old-vaccine-for-tuberculosis-protect-against-coronavirus-138006> [Accessed on 9 May 2020].
- IS BLACK TEA AN IMMUNITY BOOSTER FOR COVID- 19? | Sri Lanka (2020). [Online] Available at; <https://www.un.int/srilanka/news/black-tea-immunity-booster-covid-19> [Accessed on 9 May 2020].
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