Introduction of chikungunya virus in coastal northeast Brazil

We read the article by William M de Souza and colleagues with great interest.1de Souza WM de Lima STS Simões Mello LM et al.Spatiotemporal dynamics and recurrence of chikungunya virus in Brazil: an epidemiological study.Lancet Microbe. 2023; 4: e319-e329Summary Full Text Full Text PDF Scopus (0) Google Scholar Their study traces chikungunya virus (CHIKV) since its introduction in Brazil around 2013, and highlights spatial variability in viral spread. Among other laboratory tests, they consider people with CHIKV IgG or IgM antibodies as having confirmed infections. However, alphaviral antigenic relatedness2Fischer C Jo WK Haage V Moreira-Soto A de Oliveira Filho EF Drexler JF Challenges towards serologic diagnostics of emerging arboviruses.Clin Microbiol Infect. 2021; 27: 1221-1229Summary Full Text Full Text PDF Scopus (0) Google Scholar can compromise serological diagnosis of past CHIKV infections. In northeast Brazil, the 600 000-inhabitant city of Feira de Santana, located in the hinterland of the Brazilian state Bahia, is a CHIKV hot spot.3Nunes MRT Faria NR de Vasconcelos JM et al.Emergence and potential for spread of Chikungunya virus in Brazil.BMC Med. 2015; 13: 102Crossref PubMed Scopus (295) Google Scholar To probe CHIKV introduction into coastal northeast Brazil, we analysed CHIKV-specific antibodies in 2074 serum samples from asymptomatic patients attending the HIV outpatient clinic at Hospital Universitário Professor Edgard Santos, Salvador, for antiretroviral therapy and CD4 cell count monitoring from 2007 to 2021. Salvador is about 100 km from Feira de Santana and the biggest city in northeast Brazil with about 3 million inhabitants, ecologically highly suitable for Aedes-borne infections as illustrated by the explosive spread of Zika virus.4Netto EM Moreira-Soto A Pedroso C et al.High Zika virus seroprevalence in Salvador, northeastern Brazil limits the potential for further outbreaks.MBio. 2017; 8: e01390-e01417Crossref PubMed Scopus (137) Google Scholar Our results showed that CHIKV IgG ELISA detection rates increased during 2014 onwards compared with 2007–13; from 2·0% (n=12; 95% CI 2·0–3·4) to 18·0 % (n=262; 17·9–20·0; χ2, p<0·0001). The increase in IgG seroprevalence and the detection of two epidemic CHIKV waves paralleled notified cases from Bahia, suggesting robustness of our data (appendix p 1). Using a custom-made pan-alphavirus immunofluorescence IgG assay (IFA) for ELISA-positive sera, we found cross-reactivity with Mayaro virus (MAYV), Ross River virus (RRV), and O’nyong’nyong virus (ONNV) at lower dilution steps (1:10) in serum samples from both periods (appendix p 2). Endpoint titration improved specificity but was not enough to diagnose CHIKV confidently, as cross-reactivity with ONNV or MAYV was still present at higher dilutions (1:100) and no reactivity overall was detectable at 1:1000 serum dilution (appendix p 2). All ELISA-positive samples before 2014 were negative by CHIKV-specific plaque reduction neutralisation tests (PRNT)50; in contrast, 30 (78·9%, 95% CI 63·6–88·9; Fisher's exact test p<0·0001) of a randomly selected subset of 38 post-2014 ELISA-positive samples were positive by CHIKV PRNT50 at a median endpoint titre of 1:102 (range 1:23–540). Likewise, post-2013 samples yielded significantly higher CHIKV IgG ELISA ratios (Welch's t-test p=0·029), which is consistent with the onset of CHIKV circulation and false-positive ELISA results pre-2014. One IgG ELISA-reactive sample from 2016 yielding equal IFA reactivity patterns for CHIKV, ONNV, and MAYV at 1:10 serum dilution showed a MAYV-specific PRNT titre of 1:180, whereas no neutralisation of CHIKV was detected (appendix p 3). Comparing all ELISA results validated by PRNT (appendix p 3), we found a low positive predictive value (60·0%, 95% CI 45·2–73·6) and a high negative predictive value (96·0%, 78·9–99·9) for IgG ELISA. Those data were consistent with high false-positive ELISA rates in febrile patients from Salvador during low CHIKV circulation.5Kikuti M Tauro LB Moreira PSS et al.Evaluation of two commercially available chikungunya virus IgM enzyme-linked immunoassays (ELISA) in a setting of concomitant transmission of chikungunya, dengue and Zika viruses.Int J Infect Dis. 2020; 91: 38-43Summary Full Text Full Text PDF PubMed Scopus (13) Google Scholar In addition to cross-reactivity of alphaviral immune responses, false-positive ELISA results in our cohort could be due to HIV-induced polyclonal B-cell activation.6Shirai A Cosentino M Leitman-Klinman S Klinman D Human immunodeficiency virus infection induces both polyclonal and virus-specific B cell activation.J Clin Investig. 1992; 89: 561-566Crossref PubMed Google Scholar Altogether, our data emphasise the necessity of confirmation of results from less specific tests such as ELISA by PRNT—while acknowledging lower sensitivity of the latter—particularly beyond epidemics, since IFA testing also did not yield unambiguous results. Our results suggest CHIKV introduction into Salvador during late 2013 to 2014 followed by gradually increased circulation, which is consistent with the first notified chikungunya case from Bahia during September, 2014 (appendix p 1). Our data align with the authors’ data on spatial spread variance, and underline the necessity of addressing serological cross-reactivity for precise alphavirus infection diagnostics, particularly in areas of co-endemicity of different alphaviruses, such as MAYV and CHIKV in Latin America.2Fischer C Jo WK Haage V Moreira-Soto A de Oliveira Filho EF Drexler JF Challenges towards serologic diagnostics of emerging arboviruses.Clin Microbiol Infect. 2021; 27: 1221-1229Summary Full Text Full Text PDF Scopus (0) Google Scholar We declare no competing interests. This study was supported by the DFG project COALITION (project number DR 810/6-1), the European Union's Horizon 2020 Research and Innovation Program through the ZIKAlliance project (grant number 734548), and the Host Switching Pathogens, Infectious Outbreaks and Zoonosis (HONOURS) innovative training network (grant number 721367). All samples were collected and tested under permit number 1.408.499 issued by the Federal University of Bahia research ethics board Climério de Oliveira. Download .pdf (.5 MB) Help with pdf files Supplementary appendix Spatiotemporal dynamics and recurrence of chikungunya virus in Brazil: an epidemiological studySpatial heterogeneity of CHIKV spread and population immunity might explain the recurrence pattern of chikungunya in Brazil. These results can be used to inform public health interventions to prevent future chikungunya epidemic waves in urban settings. Full-Text PDF Open Access