An Outbreak of Arboviral Infection in a Region with Background Malaria Endemicity from Northwestern Nigeria: An Investigation Report.

INTRODUCTION

Arboviruses are a group of infectious agents transmitted by blood-sucking arthropods from one vertebrate host to another. The agents include Dengue fever and West Nile Virus, amongst others. However, Dengue fever is now the world's fastest-spreading tropical disease, with the annual number of cases increasing 30-fold in the last 50 years. Cases of an unknown febrile illness were reported in Sokoto, northwestern Nigeria, in the last quarter of 2016. We investigated to verify the existence of the outbreak and described the socio-demographic characteristics and management outcome of the cases seen.

METHODS

We conducted a descriptive, cross-sectional study and an analytical case control study. For the descriptive study, we defined suspected and confirmed cases of outbreak using established protocol. Cases were identified using stimulated passive and active surveillance. For each suspected case, we collected information on age, sex, residence and time of onset. We described the outbreak by time, place and person. Blood specimens were collected and submitted to the reference laboratory for detection of viral agents. We conducted a case-control study with 185 cases and 370 controls. Information on the socio-demographics and risk factors for arboviral infection and malaria among the cases and controls was collected.

RESULTS

The outbreak of febrile illness in Sokoto started on the 3rd of October, 2016. A total 1477 cases were line listed (3rd Oct-11th November 2016) and 16 deaths (case fatality rate: 1.1% reported). The most affected areas were urban slums in two urban Local Government Areas (LGA) - Sokoto North and Sokoto South. Laboratory analysis revealed Dengue, West Nile and Malaria in increasing order from the representative samples. There were 57 (43.2%) respondents in the age-group 21-30 among the cases, while 99 (53.5%) of them were males. Cases living in a bushy neighborhood (OR=1.6, 95% CI=1.1-2.4), keeping waste bins in their houses (OR=1.5, 95% CI=1.0-2.1), having uncovered well or uncovered water containers (OR=3.6, 95% CI=2.1- 6.0) were more likely to develop arboviral infection or malaria compared to controls. Having window nets (OR=0.3, 95% CI=0.2-0.5) was found to be a protective factor against arboviral infection or malaria among the cases.

CONCLUSIONS

The outbreak of febrile illness in Sokoto was linked to arboviral agents (Dengue virus and West Nile virus) in a malaria-endemic zone. We draw attention to the fact that arboviral infections can coexist with malaria in our region especially in an outbreak setting.