Evaluation of antigen and antibody assays for surveillance of Lassa virus in peri-domestic rodents in southeastern Sierra Leone: a cross-sectional study

<h2>Summary</h2><h3>Background</h3> Lassa fever, caused by Lassa mammarenavirus (LASV), is a rodent-borne disease endemic to west Africa. Zoonotic surveillance of LASV provides epidemiological insights into its potential presence. We aimed to assess LASV antigen and antibody prevalence in peri-domestic rodents in southeastern Sierra Leone. <h3>Methods</h3> In this cross-sectional study, small mammal trapping was conducted in Kenema District, Sierra Leone, from Nov 8, 2018 to July 10, 2019. LASV antigen was detected with a nucleoprotein antigen rapid diagnostic test at necropsy, then compared with gold-standard quantitative RT-PCR in a subset of specimens to assess specificity and sensitivity. LASV IgG antibodies against nucleoprotein and glycoprotein were tested using a semi-quantitative ELISA in <i>Mastomys</i> and <i>Rattus</i> species. <h3>Findings</h3> Of the 373 specimens tested, 74 (20%) were positive for LASV antigen. Compared with qRT-PCR, antigen testing showed a specificity of 61·9% (95% CI 52·5–70·6) and sensitivity of 100·0% (95% CI 2·5–100·0%). 40 (11%) specimens tested positive for LASV nucleoprotein-specific IgG, whereas an additional 12 (3%) were only positive for LASV glycoprotein-specific IgG, respectively. Simultaneous antigen and IgG antibody presence was observed in some <i>Mastomys</i> sp specimens (odds ratio 0·43 [95% CI 0·24–0·73], p=0·0011). However, the relative strength of antigen response did not explain the variability in the IgG response to either glycoprotein (ρ 0·04 [95% CI –0·34 to 0·41], p=0·85) or nucleoprotein (ρ –0·23 [95% CI –0·52 to 0·11], p=0·17). <h3>Interpretation</h3> Although further evaluation is needed, the tools used in this study can aid in generating valuable public health data for LASV surveillance and in prioritising specimens for further downstream analyses. <h3>Funding</h3> National Institute of Allergy and Infectious Diseases of the National Institutes of Health.