INTRODUCTION
Peste des petits ruminants (PPR) is a virus that infects mainly goats and sheep. The disease was first described in 1942 in Côte d’Ivoire (Gargadennec, 1942). Small ruminant plague virus (PPRV) was isolated for the first time in 1967 (Bourdin and Laurent-Vautier, 1968). The PPRV is a virus of the family Paramyxoviridae and genusMorbillivirus (Gibbs, et al., 1979). As a disease with economic impact, PPR is on the list of diseases to notify the International Office of Epizootics (OIE, World Animal Health Organization) in the event of emergence. It is now the subject of a global eradication program launched by OIE (International Organization Epizootics) and FAO (Food and Agriculture Organization of the United Nations) (FAO and OIE., 2015). PPRV infection is mostly by contact. The PPRV-related morbidity in a flock can reach 100% and mortality is estimated at 90% (Singh, et al., 2009). PPRV genome, composed of a single strand negative RNA with a length of 15, 948 nucleotides that encodes six structural proteins: the nucleoprotein (N), the phosphoprotein (P), the template or matrix protein (M), the fusion protein (F), the hemagglutinin protein (H) and the RNA-dependent viral polymerase (L), as well as two non-structural proteins C and V (has no meaning). Apart from the endemic presence of PPR in sub-Saharan Africa from the past decades, in recent years, field data and laboratory findings have confirmed the dramatic spread of PPR towards the south of Africa, affecting Gabon, the Democratic Republic of Congo, Somalia, Kenya and Tanzania. An outbreak of PPR was reported for the first time in October 2012 in Angola and in July 2015 in Zambia (Baron et al. 2016). The risk of PPR introduction is now high for neighbouring countries with major sheep/goat populations, such as the Republic of South Africa and Mozambique. In addition to the spread in Africa, many Asian countries are now infected, including China. After an initial identification in Tibet in 2007 (Wang et al. 2009), this country experienced a major PPR epizootic in 2013–2014 (Wang et al. 2009). PPRV is classified into 4 genetically distinct lines namely ”lineage I” to ”lineage IV”. The current molecular characterization of PPRV is typically based on the analysis of the partial sequence of the nucleoprotein gene (N, 255 nucleotides, Couacy-Hymann, E. et al., 2002). Lineage I is represented mainly by strains that circulated in West Africa in the 1970s-90s (Figure 1). It was presumed extinct, but a recent article has shown that it circulated in Niger until at least 2001 (Tounkara, K. et al., 2018). Nevertheless, it seems that lineage I has been mostly replaced by lineage II, which has spread throughout West Africa (Ashley C. Banyard et al., 2010). Lineage III is found in East Africa, Sudan, Yemen and Oman. Lineage IV was first identified in India in 1987 (Senthil Kumar, et al., 2014; Parida, et al., 2016), before spreading rapidly in the peninsula in the Middle East and on the African continent (Kwiatek, et al., 2011; Tounkara, et al., 2018; Mantip, et al., 2016). This lineage is currently rapidly spreading in West Africa, notably through extensive and poorly controlled transboundary animal movements (Tounkara et al, 2019; Souley et al 2019).
In Nigeria, sheep and goats are widespread, across different ecological and climatic zones of the country (Figure 2). It is estimated that these animals provide more than 35% of total animal protein consumption in the country (Mantip, et al., 2016). The total industrial value of small ruminants in Nigeria is around 40 billion naira (~ 100 million euros, (Shamaki, 2002). The results obtained in previous studies suggest that PPR remains an endemic disease in the country, accompanied by sporadic epidemics (Shamaki, 2002; Woma, et al., 2016; Mantip, et al., 2016a). In addition, areas where the disease was considered as being exotic in the past are the places today of regular epidemics due to an increase in trade and commerce. Molecular characterization of PPRV based on amplification and sequencing of N gene fragments in these studies showed the presence of two distinct PPRV lineages: lineage II and IV (Mantip, et al., 2016; Woma, et al., 2016). Due to the consequences of PPRV on production of animals that are of paramount importance to the economy and food security in Nigeria, it is necessary to understand its spread in the country (Mantip, et al., 2016b). In the classification of PPRV strains, there are four genetic lineages based on the sequence of the fusion (F) or nucleoprotein (N) gene (lineages I-IV). Recently, lineage IV was found to circulate alongside lineage II in Nigeria, indicating that at least two different PPRV lineages are currently circulating in Nigeria (Mantip, et al., 2016; Woma, et al., 2016). Lineage IV has historically been found in the Middle East and Asia, but has entered Africa around or before 2000, spreading into several neighbouring countries (Kwiatek, et al., 2011 ; Mantip, et al., 2016). In this study, samples were analysed from 268 small ruminants with PPR symptoms across Nigeria in 2017-2018 to provide an update on the distribution and genetic diversity of the lineage II and IV in the country.
MATERIALS AND METHODS