Chikungunya is an important re-emerging mosquito-borne disease caused by Chikungunya virus (CHIKV), an alphavirus belonging to virus family Togaviridae.1 It is vectored by Aedes species and transmitted through mosquito-to-man or man-to-mosquito interaction in urban centers. In Africa, sylvatic transmission is between these mosquitoes and non-human primates. Virus circulation is sustained in inter-epidemic periods.2 Chikungunya is an acute illness characterized by high fever, joint pain, muscle pain, and skin rash.3 It may progress to a chronic condition with debilitating arthritis, if primary infection does not resolve.4 Mothers infected during pregnancy can transmit CHIKV to their newborns5 resulting in neonatal encephalopathy, thrombocytopenia, hypotension, pericarditis, and neurologic manifestations.6 CHIKV has been identified in almost 40 countries around the world. In 2016, a total of 146,914 confirmed cases from the Americas were reported to the Pan-American Health Organization. Although the burden in many African countries is unknown, that same year 1700 suspected cases were reported from Kenya.7 Reports of CHIKV was first made in Nigeria in 1964,8 and it continues to cause significant health problems with reports of overseas importation from Nigeria.9 It is now emerging in parts of the world where it had never been reported.10 It was recently reported in Europe and USA, raising concerns of associated risk following increased international travel to endemic areas of the world.11 Other factors that facilitate spread includes trade in products with vector larvae, climate change which supports vector survival, and lack of herd immunity.12 In developing countries such as Nigeria, malaria or typhoid is the tentative diagnosis for most febrile illnesses. Clinicians seldom consider arboviral infections, despite the fact that they produce clinically similar symptoms.13 Consequently, there is underreporting, increased morbidity and mortality from arboviral infections.14 There is currently no information on CHIKV infection in Kogi State. Nigeria is the most populous country in Africa, and Kogi State is the gateway to Northern and Southern parts of the country with usually heavy vehicular traffic as people transit the nooks and crannies of the nation, including international visitors. This study determined seroprevalence of antibodies against previous and current CHIV infection to provide preliminary data and inform policy decisions for environmental vector control and health promotion. It also provides socio-demographic and clinical tools to guide differential diagnosis of these arbovirosis.

There were 110 (45.3%) males and 133 (54.7%) females between five and 80 years of age. Participants were mostly in the age-range of 30–44 years (34.2%) while 2.5% were in age group 75–80 years (Table 1). Out of 243 febrile participants screened, 14 (5.8%) had anti-CHIKV IgM, 61 (25.1%) had anti-IgG and 8 (3.3%) had both IgG and IgM. Overall prevalence of 34.2% (83/243) was observed (Table 1). IgM and IgG seropositivity was significantly associated with male sex (p=0.044, X2=4.075). Males had almost two-fold greater chance of contracting CHIKV compared to females (OR=1.7, CI=1.014–2.955). CHIKV seropositivity increased with age,a s shown in Fig. 1 (p<0.001). Active CHIKV infection was found in all age groups, but more common in people older than 75 years. Active infection was lowest in age group 5–14 years. Dual seropositivity was more observed in married people compared to divorced, widowed and single individuals (p=0.002; Table 2). With exception of those with primary level of education, there was increasing trend in seropositivity as educational level increased. Farmers had higher prevalence of current infection (48.1%), followed by people who engaged in business activities. Significant association was observed between participant’s occupation and active infection (p<0.001). Insecticide users had higher seropositivity (41.6%) compared to non-users (29.2%). Fever (10.8%), abdominal pain (10.8%), and diarrhea (9.5%) were associated with high IgM levels and dual (IgG and IgM) seropositivity. However, this was not statistically significant (Table 3). Significant association was observed between joint pain and IgG seropositivity (p=0.042). Participants who were confirmed with malaria were twice more likely to have been previously exposed to Chikungunya (p=0.033, OR=2.0, CI: 1.051–3.997).

Fig. 1.

Prevalence of CHIKV antibodies in febrile patients in Anyigba according to age group.

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High IgG seropositivity obtained in this study indicates Chikungunya is endemic in Kogi State. Together with few reports from other parts of Nigeria, findings from our study underscore the fact that mosquitoes spread easily across parts of Nigeria. The derived Savannah where Kogi State is located serves as a buffer zone. It is possible that this area sustains CHIKV for onward transmission to the arid northern part, as visitors on transit are bitten by the vectors. Dual IgG and IgM positivity observed among participants in this study indicates ongoing infection despite previous exposure. Both immunological markers translate past and ongoing or acute infections,17,18 suggesting CHIKV is maintained at an endemic threshold within the area. Age was found to be an important factor for active CHIKV infection, as shown in Fig. 1. Higher rates observed in age group 60–74 years is in agreement with previous reports among older patients in Chandrapur and Singapore.19,20 In those reports, direct relationship was found between increasing age and susceptibility to CHIKV. This is a result of anatomical and functional changes, degree of exposure, and impaired immune functions especially among the geriatric population.19 Furthermore, elderly people maintain sedentary lifestyles as they sit for long periods in unscreened places, thereby being exposed to Aedes species. Males were more exposed to CHIKV in the present study, despite having more febrile females visiting the health facilities (Table 1). This sex bias has been previously reported20–22 and may be attributed to cultural habits and behaviours which predispose males to more bites by Aedes species. Men are more adventurous; they hunt and fend for the family, irrespective of the place and time. They enter forested areas, swamps, and may not protect themselves from mosquito bites. Higher seroprevalence observed among patients with tertiary education may be due to increased outdoor physical activity or sedentary lifestyle in places infested by Aedes species without protection against vectors. Active infection was observed to occur more in married participants (Table 2). This has been corroborated by studies in two south-western states in Nigeria.16 Couples are usually in close proximity compared to widows or widowers, if one partner acquires infection the other partner can be horizontally infected following blood meal by vector. Indeed, transmission can affect their children which by implication is the single or unmarried person living in the household. Incidentally, infected mosquito can easily spread CHIKV to family members. Working on farms and agricultural fields was associated with higher CHIKV seropositivity (Table 2). This was also observed in Chandrapur, India23 and may be the result of frequent exposures while on their farmlands. As water collects in poodles or from watering crops, there is increased mosquito activity which predisposes farmers to bites by Aedes species.

Fever, abdominal pain and dysentery are predominant acute symptoms associated with CHIKV in this study. Similarly, same symptoms were previously observed among people in India.24 Joint pain was significantly associated with past CHIKV infection. This agrees with reports in Tanzania and Ethiopia where joint pain was a common finding among people with CHIKV.25,26 Some participants were co-infected with malaria and CHIKV in this study. Both are mosquito-blood-borne infections and not mutually exclusive. This is why it is very difficult to distinguish clinically between malaria and arboviral infections, leading to misdiagnoses. Immunosuppressive nature of malaria27 may lead to increased risk of acquiring active CHIKV infection. A limitation in our present study is that only symptomatic patients were considered, whereas Chikungunya infection may be asymptomatic. Thus, it is possible to detect both antibodies in apparently healthy population.

In conclusion, this study shows CHIKV is actively circulating in Anyigba. It highlights the need to rule out differential causes of arboviral infections. This is the first CHIKV serosurveillance in Kogi State. If control measures are not instituted, it portends major health threat because it is located in the middle belt which serves as transit point for travellers from north and south. It reinforces inclusion of CHIKV surveillance and routine screening for other arboviruses in febrile patients. CHIKV infection requires prompt attention because there is currently no vaccine. There is need for vector control strategies, intensive awareness creation through media, evacuation of gutters and clearing of bushes.

The authors declare no conflicts of interest.

No specific funding was received for this project.