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