Seroepidemiology of Lassa virus in pregnant women in Southern Nigeria: A prospective hospital-based cohort study

Abstract

There is limited epidemiological evidence on Lassa fever in pregnant women with acute gaps on prevalence, infection incidence, and risk factors. Such evidence would facilitate the design of therapeutic and vaccine trials and the design of control programs. Our study sought to address some of these gaps by estimating the seroprevalence and seroconversion risk of Lassa fever in pregnant women. We conducted a prospective hospital-based cohort between February and December 2019 in Edo State, Southern Nigeria, enrolling pregnant women at antenatal clinic and following them up at delivery. Samples were evaluated for IgG antibodies against Lassa virus. The study demonstrates a seroprevalence of Lassa IgG antibodies of 49.6% and a seroconversion risk of 20.8%. Seropositivity was strongly correlated with rodent exposure around homes with an attributable risk proportion of 35%. Seroreversion was also seen with a seroreversion risk of 13.4%. Our study suggests that 50% of pregnant women were at risk of Lassa infection and that 35.0% of infections might be preventable by avoiding rodent exposure and conditions which facilitate infestation and the risk of human-rodent contact. While the evidence on rodent exposure is subjective and further studies are needed to provide a better understanding of the avenues of human-rodent interaction; public health measures to decrease the risk of rodent infestation and the risk of spill over events may be beneficial. With an estimated seroconversion risk of 20.8%, our study suggests an appreciable risk of contracting Lassa fever during pregnancy and while most of these seroconversions may not be new infections, given the high risk of adverse outcomes in pregnancy, it supports the need for preventative and therapeutic options against Lassa fever in pregnancy. The occurrence of seroreversion in our study suggests that the prevalence obtained in this, and other cohorts may be an underestimate of the actual proportion of women of childbearing age who present at pregnancy with prior LASV exposure. Additionally, the occurrence of both seroconversion and seroreversion in this cohort suggests that these parameters would need to be considered for the development of Lassa vaccine efficacy, effectiveness, and utility models. Lassa virus is a viral haemorrhagic fever endemic to West Africa and yet to date there is limited information on its epidemiology in pregnancy. Information obtained from epidemiology studies is important because such information facilitates the design and costing of disease control programs and the design of clinical trials. Our study evaluated the epidemiology of Lassa fever in pregnant women specifically we looked at the prevalence, incidence, and risk factors for infection in pregnant women in South Nigeria. We found that 49.6% of pregnant women had antibodies to Lassa virus suggesting about 50% of pregnant women were at risk of Lassa infection. Additionally, while, the evidence was not conclusive, we found an appreciable risk of contracting Lassa fever during pregnancy. Given that, Lassa fever has high case fatality in pregnancy, our data supports the need for vaccines and drugs against Lassa fever. Our study also suggests that 35.0% of infections might be preventable by avoiding rodent exposure and conditions which facilitate rodent infestation and the risk of human-rodent contact. This suggests that public health measures such as proper sanitation and hygiene, improved housing and health education may be beneficial in reducing the risk of infection.