Long-term persistence of serum IgM antibodies against chikungunya virus in patients with chronic arthralgia

BACKGROUND: Anti-Chikungunya virus (CHIKV) IgM antibodies may persist for months after infection in some individuals, but the evidence is limited, and their exact duration remains unknown. OBJECTIVE: This study aimed to determine the duration for which anti-CHIKV IgM antibodies remain detectable following acute infection. METHODS: A commercial ELISA was used to assess the frequency of anti-CHIKV IgM antibody detection over time in 145 longitudinal serum samples obtained from 45 laboratory-confirmed chikungunya patients in Brazil (two to six samples per patient). RESULTS: Among samples obtained within seven days post-symptom onset (DPSO), 13% (6/45) were IgM-positive. Between 10 and 120 DPSO, 100% (62/62) of samples were positive. Positivity rates for samples collected between 121 - 720, 721-900, 901-1,080, 1,081-1,260, and > 1,260 DPSO were 62% (5/8), 35% (6/17), 12% (1/8), 33% (1/3) and 50% (1/2), respectively. Notably, among 21 patients who developed chronic arthralgia and had at least one sample collected > 720 DPSO, 7 (33%) still had detectable anti-CHIKV IgM. This suggests that approximately one-third of chikungunya patients with chronic arthralgia may maintain anti-CHIKV IgM for over two years following acute disease. CONCLUSIONS: Our findings indicate that anti-CHIKV IgM antibodies can persist substantially longer than typically observed for acute RNA virus infections. This has significant implications for chikungunya diagnosis and surveillance. Further research is needed to determine whether long-term IgM persistence also occurs in patients without chronic chikungunya symptoms.