Complex Circulation of Foot-and-Mouth Disease Virus in Cattle in Nigeria

Abstract

Nigeria is a large densely populated country in West Africa. Most of its livestock is raised in a pastoralist production system with typical long distance migration in search of water and feed. As the demand for animal products largely exceeds the domestic production, large numbers of livestock are imported from neighboring countries without sanitary restrictions. In Nigeria, foot-and-mouth disease virus (FMDV) serotypes O, A, and Southern African Territories (SAT)2 are endemic for a long time. Clinical outbreaks of FMD due to serotype SAT1 are described again since 2015, after an absence of more than 30 years. Historically, outbreaks of FMD due to serotypes O, A, SAT1, and SAT2 were each time associated with trade of cattle entering Nigeria from neighboring countries. In the present study, tissue samples from 27 outbreaks of FMD were collected in Nigerian cattle from 2012 until 2017 in six different States and in the Federal Capital Territory. FMDV was isolated and serotyped and further characterized by VP1 sequencing and phylogenetic analysis to gain more knowledge on FMDV circulation in Nigeria. Half of the outbreaks were characterized as FMDV topotype O/EA-3, while outbreaks with other serotypes and topotypes were-in descending order-less prevalent: A/Africa/G-IV, SAT1/X, SAT2/VII, and O/WA. The high dynamics and omnipresence of FMD in Nigeria were illustrated in Plateau State where FMDV serotypes O, SAT1, and SAT2 were isolated during the course of the study, while at some point in the study, outbreaks due to FMDV serotype A were observed in three remote States. The genetic and phylogenetic analysis suggests a mixed origin of FMD outbreaks. Some outbreaks seem to be caused by sustained local transmission of FMDV strains present in Nigeria since a number of years, while other outbreaks seem to be related to recent incursions with new FMDV strains. The role of African buffaloes in the etiology of FMD in Nigeria is unclear, and sampling of wildlife is needed. The results of the present study suggest that systematic sample collection is essential to understand the complex concomitance of FMDV strains in Nigeria and essential to support the implementation of a vaccination-based control plan.

Keywords: Nigeria; VP1; foot-and-mouth disease (FMD); foot-and-mouth disease virus; phylogeny; topotypes.

Figure 1

Geographical distribution and serotypes of foot-and-mouth disease virus (FMDV) isolates collected in Nigeria between 2012 and 2017. The geopolitical zones and the Federal Capital Territory (FCT) are indicated.

Figure 2

VP1 phylogenetic tree for foot-and-mouth disease virus (FMDV) serotype O inferred using the maximum likelihood method based on the Tamura-Nei model. Branch lengths indicate the number of substitutions per site. Bootstrap values ≥60% are indicated at the nodes. Novel Nigerian FMDV from this study from Plateau is indicated with ▼, from Kaduna with • and from Bauchi with ■.

Figure 3

VP1 phylogenetic tree for foot-and-mouth disease virus (FMDV) serotype A inferred using the maximum likelihood method based on the Tamura-Nei model. Branch lengths indicate the number of substitutions per site. Bootstrap values ≥60% are indicated at the nodes. Novel Nigerian FMDV from this study from Kaduna is indicated with •, from Bauchi with ■, from Oyo with ▴ and from Benue with ♦.

Figure 4

VP1 phylogenetic tree for foot-and-mouth disease virus (FMDV) serotype Southern African Territories (SAT)1 inferred using the maximum likelihood method based on the Tamura-Nei model. Branch lengths indicate the number of substitutions per site. Bootstrap values ≥60% are indicated at the nodes. Novel Nigerian FMDV from this study from Plateau is indicated with ▼.

Figure 5

VP1 phylogenetic tree for foot-and-mouth disease virus (FMDV) serotype Southern African Territories (SAT)2 inferred using the maximum likelihood method based on the Tamura-Nei model. Branch lengths indicate the number of substitutions per site. Bootstrap values ≥60% are indicated at the nodes. Novel Nigerian FMDV from this study from Plateau is indicated with ▼ and from Abuja FCT with ⚬.