A Cross-Sectional Serosurvey of Anti-Orthopoxvirus Antibodies in Central and Western Africa

Abstract

Since the eradication of smallpox and the subsequent discontinuation of the worldwide smallpox vaccination program, other Orthopoxviruses beside Variola virus have been increasingly representing a risk to human health. To investigate the extent of natural contact with Orthopoxviruses and possible demographic risk factors for such an exposure, we performed a cross-sectional serosurvey of anti-Orthopoxvirus IgG antibodies in West and Central Africa. To this end, people living in forest regions in Côte d'Ivoire (CIV, n = 737) and the Democratic Republic of the Congo (COD, n = 267) were assigned into groups according to their likely smallpox vaccination status. The overall prevalence of anti-Orthopoxvirus antibodies was 51% in CIV and 60% in COD. High rates of seropositivity among the vaccinated part of the population (80% in CIV; 96% COD) indicated a long-lasting post vaccination immune response. In non-vaccinated participants, seroprevalences of 19% (CIV) and 26% (COD) indicated regular contact with Orthopoxviruses. Multivariate logistic regression revealed that the antibody level in the vaccinated part of the population was higher in COD than in CIV, increased with age and was slightly higher in females than males. In the unvaccinated part of the population none of these factors influenced antibody level significantly. In conclusion, our results confirm expectedly high anti-Orthopoxvirus seroprevalences in previously smallpox-vaccinated people living in CIV and the COD but more unexpectedly imply regular contact with Orthopoxviruses both in Western and Central Africa, even in the absence of recognized outbreaks.

Keywords: ELISA (enzyme linked immunosorbent assay); orthopoxvirus; seroprevalence; zoonoses.

Figure 1

Rural sampling locations near Taï National Park, Côte d’Ivoire (left panel) and Salonga National Park, Democratic Republic of the Congo (right panel). National Parks in dark green. 1, Zagne (Zag). 2, Tienkoula (Tie). 3, Goulegui Beoue (GouB). 4, Djiboubaye (Dji). 5, Keibly (Kei). 6, Zaipobly (Zai). 7, Gahably (Gah). 8, Daobly (Dao). 9, Ponan (Pon). 10, Taï (Tai). 11, Gouleako (Gou). 12, Pauleoula (Pau). 13, Portgentil (Por). 14, Djereoula (Dje). 15, Tienkoula (Tien). 16, Tieleoula (Tiel). 17, Ziriglo (Zir). 18, Sakre (Sak). 19, Bekombo (Bek). 20, Lompole (Lom). 21, Ipope/Nganda (Ipo/Nga).

Figure 2

Comparison of ELISA (enzyme linked immunosorbent assay results) (antibody level) and IFA (immunofluorescence assay) titer (A) or neutralization assay ((B) XCelligence Cell Index) for a panel of sera ((A) n = 100; (B) n = 50) collected from German blood donors.

Figure 3

Antibody levels in human participants in CIV and COD. The red horizontal line indicates cut-off value for positive samples. The blue vertical line represents time of vaccination cessation; the green vertical lines indicate the 5-year margins on either side.

Figure 4

Mean antibody levels in the villages where specimens were taken. The names of the villages are abbreviated to the first three or four letters of the name. The first 18 villages on the left are in CIV, the 4 on the right hand side represents villages in COD.