Chikungunya fever is a mosquito-borne viral disease caused by Chikungunya virus (CHIKV). Its name derives from a Makonde word translated as ‘disease that bends up the joints’, which describes the posture of afflicted individuals feeling severe joint pain or arthralgia [1]. Other symptoms include abrupt fever, muscle pain, headache, nausea, fatigue, and rash. These symptoms are often mild, and the infection may go unrecognized or not accurately diagnosed, in particular in regions where other infections caused by Dengue virus (DENV) and Zika virus (ZIKV) occur.
CHIKV was first isolated in 1952 in Tanzania [1] and has reemerged within a span of several years in South East Africa and Asia [2]. In December 2013, CHIKV reached the Americas [3]. It was first reported on St. Martin in the Caribbean and within weeks in other neighboring islands. The first CHIKV report in Mexico was in May 2014 from a patient in Jalisco, who showed CHIKV infection symptoms after a trip to the Caribbean region [4]. Other reports followed in October 2014 in Chiapas. [5, 6]. By 2015, more than one thousand cases occurred mostly in the southern region of the country, where warm and humid zones are amenable to mosquito growth. Overall, more than three million CHIKV infections have been reported in Mexico, Central and South America, with over 500 deaths directly or indirectly related to this viral disease [7].
While CHIKV infection is not currently considered a public health concern with only three cases reported by mid-2019 (www.gob.mx/salud/acciones-y-programas/chikungunya-informacion-relevante), Chikungunya fever outbreaks are recurrent [2, 8]. Some of the factors contributing to such a recurrence are an inadequate disease surveillance and underdiagnosis, virus evolution and mutation rate, new generations of individuals with no immunity to the virus, supply chains globalization, travelling, and climate change. Since no approved vaccine nor antiviral CHIKV therapeutics exist, early detection and appropriate disease management are the only tools at the disposal of the scientists, health care community and governments to control future CHIKV outbreaks and reduce their devastating social and economic impacts.
Some of the detection methods of CHIKV infection are based on virus isolation, reverse transcriptase polymerase chain reaction (RT-PCR) [9] and IgM ELISA [10]. Since virus isolation requires highly secure (BSL-3) facilities, PCR-based methods are mostly used for early and accurate diagnosis. Nonetheless, relatively high cost of the assay and the requirement of a thermal cycler to conduct the test limit its application in the field and rural regions where outbreaks often occur. Immunochemical methods such as IgM ELISA can be applied everywhere and are cost-effective, but it takes around a week for the patient to develop an antibody response. Hence, this diagnosis method is not effective in early stages of the infection.
Alternatively, direct CHIKV detection in serum has been reported as an early and reliable clinical diagnosis as well as an effective surveillance of CHIKV [11–13]. Some of the assays relies on anti-CHIKV monoclonal antibodies generated by hybridoma technology after immunization with inactivated CHKV particles or recombinant proteins [13, 14]. Virus-like particles (VLPs) have also been used as selectors combined with immune libraries or B-cell sorting as source of human anti-CHIKV antibodies [15, 16]. In addition to diagnosis, such antibodies, being of human origin, if proven to neutralize the CHIKV infection, could be used as prophylactic or therapeutic drugs.
Three CHIKV major lineages known as West African (WA); East, Central, and South African (ECSA); and Asian have been described thus far [18, 19]. In addition, an Indian Ocean (IOL) sublineage emerged within the ECSA and the Asian/American sublineage emerged within the Asian lineages. The envelope of CHIKV particles contains two main structural glycoproteins, E1 and E2, which have been considered the targets in the development of diagnosis tools [13], therapeutic antibodies [15], and vaccines [17]. E2 protein shows the highest percentage of amino acid variation among the lineages and strains, impacting in some cases the interaction with the host receptor and hence modifying CHIKV clinical manifestations, virulence and even its epidemiology [20]. These changes could also modify the interaction with specific antibodies, limiting the use of such antibodies as diagnostic, therapeutic or prophylactic tools.
Here, with the goal of generating anti-CHIKV antibodies with potential application in the early diagnostic and CHIKV disease management in Mexico, we purified virions from a serum sample obtained from a patient from Veracruz, México, during the 2015 CHIKV outbreak. The integrity of the CHIKV virions was assessed by structural methods such as electron microscopy as well as functional methods such as binding to diverse well-characterized anti-CHIKV monoclonal antibodies [15, 16]. We also determined the whole genome sequence of this CHIKV isolate and compare it to genome sequences of different lineages described for CHIKV, e.g, WA, ECSA and IOL lineages.
Once qualified, UV-inactivated CHIKV particles were used as selectors to discover high affinity and highly stable antibodies from ALTHEA Gold Libraries™ [21, 22]. The specificity of the antibodies was assessed by ELISA using viral particles of Venezuelan equine encephalitis virus (VEEV), which is similar to CHIKV, both belonging to the Alphavirus genus. We also determined the cross-reactivity with DENV-1 and DENV-2, and ZIKV. These viruses co-exists with CHIKV and generate similar symptoms thus making difficult the differential diagnostic of CHIKV infection. Finally, a sandwich ELISA with the best antibody, combined with a potent neutralizing antibody reported elsewhere [15], was implemented. The results indicate that the newly discovered antibodies and the prototype ELISA developed herein could be valuable and effective tools for CHIKV disease surveillance.