Dengue is a major arthropod-borne viral disease of humans, and its control and management remain the primary priority of public health for many endemic countries. Unlike the situation in the Asia-Pacific and Latin American regions, where dengue burden and epidemiology is well documented, the burden and epidemiology of dengue virus infection in Africa including Nigeria is not clear, even though there are reported cases.
In an attempt to improve surveillance and to track the viral burden and epidemiology in Nigeria, this population-based survey was conducted in secondary and primary healthcare facilities to determine the occurrence of dengue virus infection and serotypes in Mubi, Yola North (Jimeta) and Numan LGAs in Adamawa state, Nigeria. Febrile patients with clinical signs and symptoms compatible with dengue virus infection, which were referred to a laboratory to conduct malaria parasitaemia diagnosis and who consented to participate before sample collection, were recruited into this study. Despite being undetected prior to this study active transmission of dengue virus, dengue and malaria co-infection were detected across the three study locations. A sero-prevalence of 19.4% for dengue virus infection was established.
In Mubi, out of the 146 patients, 97 (66.4%) tested positive for malaria parasites and 49 (33.6%) were negative. Twenty-nine (19.9%) of the participants were positive for dengue antibody. The age-specific range of dengue sero-prevalence was observed to be significant in the younger participants aged 6–30 years with a p-value of 0.003. This could be plausible, since these age groups are known to be actively involved in outdoor activities where possible contact with vector is very likely. A sero-prevalence of 19.9% for dengue virus IgM was obtained in Mubi. This, therefore, means that younger people within the age range of 5–30 years should be the target age for the dengue vaccination programme, if the need becomes imperative. Out of the 146 patients, 16 (11%) were found to be co-infected with dengue and malaria. This observation has brought to light the fact that examination of febrile illnesses should not be limited to parasites and bacteria, but that flaviviruses can equally cause febrile illnesses.
In Jimeta, out of the 124 patients, 83 (66.9%) tested positive for malaria parasites and 41 (33.1%) were negative. Twenty-four (19.4%) of the participants were positive for dengue antibody. The age-specific range of dengue sero-prevalence was observed not to be statistically significant in the younger participants aged 0–35 years with a p-value of 0.238. This suggests that the infection was not limited to the younger age group.
Out of the 124 patients, 18 (14.5%) were found to be co-infected with dengue and malaria. This again suggests that febrile illnesses should not be limited to malaria and typhoid but that flaviviruses infection can result in febrile illness; hence, proper laboratory diagnosis for febrile illnesses should be readily available and recommended before drugs prescription.
In Numan, out of the 154 patients, 97 (63.0%) tested positive for malaria parasites and 57 (37.0%) were negative. Twenty-nine (18.8%) of the participants were positive for dengue antibody. The age-specific range of dengue sero-prevalence was predominant in the age group of 6–25 years. This observation, however, was not statistically significant with a p-value of 0.417. Like Jimeta, dengue sero-prevalence was found across all the age groups but more pronounced in the younger age groups. Out of 154 patients, 19 (12.3%) were found to be co-infected with dengue and malaria. This further confirms that flaviviruses are capable of causing febrile illness as it was found to be present across all the study locations.
From the findings, malaria may not be the only mosquito-borne disease-causing febrile illness across the study locations. With dengue sero-prevalence rates of 19.9%, 19.4% and 18.8% in the three study locations respectively, there may be an active transmission of dengue across the entire state and possibly beyond, due to the fact that dengue is frequently being transported from one place to another by infected travelers coupled with inherent behavior pattern of the population that encourages vector breeding. The development implies that dengue may be endemic in these areas, but undetected or possibly misdiagnosed as malaria.
The co-infection of febrile patients with dengue and malaria in the study could suggest the possibility of mosquitoes carrying more than one pathogen or the presence of Aedes spp as a suitable vector across these locations. A similar scenario of dengue and malaria co-infection was reported by Ayukekbong [15] in Ibadan where 10% of malaria patients had active dengue infection. As it can be observed from the results of this study, dengue rate of occurrence was higher in Mubi (19.9%) and Jimeta (19.4%) than Numan (18.8%), even though more samples were collected from Numan than in each of these two locations. This may be so since Mubi and Jimeta are the economic hubs of the state with greater population density than Numan. The difference is not statistically significant and is only marginal.
In a recent serological survey of dengue IgM, Oladipo et al. [18] reported a 17.2% prevalence in seemingly healthy individuals in Ogbomosho, while Adesina and Adeniji [19] reported a sero-prevalence of dengue IgM of 25.7% among febrile volunteer subjects in Ile-Ife, western Nigeria.
In Jos and Ibadan, 2.2% and 35% of febrile subjects were reported to be positive for dengue nonstructural protein one (NS1) antigen among febrile subjects respectively [11]. In another separate study, Hamisu et al. [20] reported 37.4% positive for dengue IgM in Maiduguri and Bello et al. [21] in a study conducted in Kaduna reported 51.1% and 48.9% positive for dengue IgM in females and males respectively.
Only dengue virus serotype 1 was identified in the three study locations and this may highlight the active occurrence of dengue virus in the study areas. In a similar study in Ibadan, DENV serotypes 1 and 2 were detected while DENV serotype 1 was reported in Abeakuta [22]. In Lagos, Ayolabi et al. [23] reported the circulation of DENV serotypes 1 and 3 in febrile patients. In a study conducted by Yousseu et al. [24] in Douala, Cameroon, active circulation of DENV serotype 1 was reported. Parreira et al. [25] reported DENV serotype 1 to be responsible for the outbreak in Angola. However, other reports indicated that DENV serotypes 2 and 3 may cause more severe forms of dengue infection than the other serotypes [26].
The detection of DENV serotype 1 in this study could explain why severe cases of dengue virus infection due to secondary infection and cross-reactivity with other serotypes have not been reported in the three study areas. However, this does not rule out potential outbreaks and may not be the current situation as possible cases of importation of other serotypes cannot be overruled.
Currently, dengue prevention and control depends heavily on effective vector measures, hence, sustained local involvement can improve vector control efforts substantially as local risk to dengue outbreaks is linked to the population’s knowledge, attitude as well as behavioural practices that encourage vector breeding. Communities are encouraged to avoid exposure to mosquito bites especially during the day time, rid their environment of possible mosquito breeding sites as proximity of breeding sites is a significant risk factor to dengue transmission, and active community engagement through sensitization and mobilization against mosquito-borne diseases.