What is the prevalence of orthopoxviruses across different populations?

In a recent study posted to the medRxiv* preprint server, researchers assessed the prevalence of orthopoxviruses among the general populations of Bolivia, France, Laos, and Mali.

The recent emergence of the monkeypox virus (MPVX) infections has raised concerns regarding the limited knowledge about the immunities of the general populations to orthopoxviruses. To prevent the further spread of MPVX infections, research is needed to understand the magnitude of immunity displayed by different populations.

About the study

In the present study, researchers presented large-scale epidemiological research performed based on the presence of neutralizing antibodies elicited against the cowpox virus and the vaccinia virus.

The team assessed four distinct populations belonging to Bolivia, France, Laos, and Mali by testing the populations for the presence of neutralizing antibodies against the vaccinia virus. Additionally, a majority of the French population was analyzed for the presence of neutralizing antibodies against the cowpox virus.

The French population comprised 4876 voluntary blood donors who provided serological samples in 2012, 2013, and 2019. These participants resided in four different areas of metropolitan France namely Auvergne-Loire, Corsica, Midi-Pyrénées, and Provence-Alpes Côte d'Azur (PACA). The donors were asked to answer a questionnaire that queried them about their birth year, gender, as well as information regarding their lifestyle, general environment, and exposure to any zoonotic diseases.

The Bolivian population comprised 601 voluntary blood donors who provided serum samples in 2017 and resided in major cities such as Santa Cruz de la Sierra, Beni, Cochabamba, Tarija, and La Paz. Furthermore, the Laos population included 657 donors who donated serum in 2003, 2004, 2015, and 2018 in Vientiane. Lastly, the Mali population included 257 donors who provided serum samples in 2019 and resided in the villages of Bougoudale, Komana, Leba, Tliemba, and Soloba.   

Additionally, the team employed the Western Reserve vaccinia strain and the Compiègne strain of the cowpox virus. Subsequently, viral productions utilized for the sero-neutralization assay were adjusted to estimate low and comparable ratios corresponding to the non-infectious to infectious particles.

Results

The study results showed that the 4448 samples collected from the French populations displayed 98.8% similarity in the antibody titers for the cowpox and vaccinia viruses. Among these samples, the sex ratio was 1.17 while the average year of birth reported was 1966 ± 13 years. Furthermore, the difference estimated between the seroprevalence values corresponding to the vaccinia neutralization test was used to estimate the orthopoxvirus neutralization titer (ONT). The ONT was the geometric mean of smallpox and vaccinia neutralization titers while samples having ONT of 20 or more were deemed positive for that virus.

The team noted that the global seroprevalence of the orthopoxviruses was 8.18% while the same among persons born before 1970 was 10%, persons born during the 1970s was 5%, and after 1980 was 1%. The geometric mean of ONT for the entire study sample was 12.8. The team also observed considerable variations based on the age groups while an overall proportional increase was observed in the number of positive samples with respect to age.

Furthermore, the correlation between the presence of neutralizing antibodies against orthopoxviruses and gender varied based on the decade of birth of the person. Until the 1950s, seroprevalence was found to be higher among males which reduced to levels comparable to those in females in the 1960s which reduced to levels lower than those observed in women in the 1970s. From the 1980s onwards, no significant differences were noted between the participants with respect to seroprevalence.

The team also found few differences between the four French regions based on the percentage of positive samples and titers of neutralizing antibodies. Notably, the seroprevalence was higher in  Midi-Pyrénées and Corsica as compared to that in the PACA region. The Auvergne-Loire region displayed the lowest seroprevalence among the French regions assessed for each decade of birth. Overall, the study showed that the only parameter that showed a direct association with the neutralizing titers against orthopoxviruses was age.

Conclusion

The study findings showed that the different populations residing in Africa, South America, Asia, and Europe were significantly vulnerable to orthopoxvirus infections. This indicates that there exists no population immunity that could serve as a barrier against the spread of orthopoxviruses. Furthermore, the study indicated that the cessation of smallpox vaccination could potentially facilitate orthopoxvirus transmission as is evident in the increasing number of monkeypox infections observed in Europe.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.