Peste-des-petits-ruminants virus (PPRV) is a highly contagious, fatal and economically important viral disease of small ruminants that is still endemic and militates against the production of sheep and goats in endemic areas of the world. The aim of this study was to describe the viral strains within the country. This was carried out by collecting tissue and swab samples from sheep and goats in various agro-ecological zones of Nigeria. The phylogeny of archived PPRV strains or isolates and those circulating and causing recent outbreaks was determined by sequencing of the nucleoprotein (N)-gene. Twenty tissue and swab samples from apparently healthy and sick sheep and goats were collected randomly from 18 states, namely 3 states in each of the 6 agro-ecological zones visited. A total of 360 samples were collected. A total of 35 samples of 360 (9.7%) tested positive by reverse transcriptase–polymerase chain reaction, of which 25 were from oculo-nasal swabs and 10 were from tissue samples. Neighbour-joining phylogenetic analysis using Phylogenetic Analysis Using Parsimony (PAUP) identified four different lineages, that is, lineages I, II, III and IV. Interestingly, the Nigerian strains described in this study grouped in two separate major lineages, that is, lineages II and IV. Strains from Sokoto, Oyo, Plateau and Ondo states grouped according to the historical distribution of PPRV together with the Nigerian 75/1 strain of lineage II, while other strains from Sokoto, Oyo, Plateau, Akwa-Ibom, Adamawa, Kaduna, Lagos, Bauchi, Niger and Kano states grouped together with the East African and Asian strains of lineage IV. This finding confirms that both lineage II and IV strains of PPRV are circulating in Nigeria. Previously, only strains of lineage II were found to be present in the country.
Peste-des-petits-ruminants virus (PPRV) belongs to the family
Peste-des-petits ruminants (PPR) has been mistaken for rinderpest since the fourth century AD (Curasson
PPRV is distributed widely across West, Central, East and some parts of North Africa, the Arabic Peninsula, the Middle East and Asia (Nanda
PPRV is sometimes referred to as a more serious disease of goats than sheep; however, outbreaks affecting both sheep and goat populations have been reported (Chauhan
The current molecular characterisation of PPRV strains based on the N-gene divides them into four genetically distinct lineages (Banyard
Because of the adverse consequences posed by PPRV in the production of sheep and goats in Nigeria, there is a need to undertake a study of PPRV in sheep and goats from recent outbreaks across the different regions of the country. It is important to understand the spread of the pathogen within the country in comparison with other endemic areas of the world. The sequences derived from this study will provide the basis for better understanding of the epidemiology of PPRV.
The aim of this research project is to compare the sequences of recently occurring PPRV strains with previously sequenced PPRV isolates in GenBank.
Eighteen states were selected to represent the different agro-ecological zones of the country. These agro-ecological zones were aligned within the six geopolitical zones of the country for ease of reference. At present, there is no comprehensive figure for the population of sheep and goats in Nigeria, but in 1983, a population of 22 million goats and 8 million sheep was estimated (Federal Livestock Department, Lagos, Nigeria). Locations where samples were collected were marked and recorded by the use of a GPS apparatus (GARMIN) GPSMAP 76CSX with sensor.
Three states were identified randomly from each of the six agro-ecological zones and 20 samples of either oculo-nasal swabs or tissues (lung, spleen and lymph node) were collected with consent of the animals’ owners from each of the 18 states. Swabs were collected from live animals, while tissues were collected from dead animals. The locations for sampling included major towns, their surrounding villages and suburbs. Stratified sampling was used in herd or farm sites, grazing sites, market places and house backyard range. Sampling was carried out during necropsy on dead animals and from sick animals with clinical signs that resembled PPR. The total number of samples collected was 360, which comprised 169 tissue samples and 191 oculo-nasal swabs. To ensure that the quality of the samples was maintained from the field to the laboratory, samples were always kept on iceblocks in a sample collection flask.
Necropsy tissues were processed based on the standard operating procedure of the PPR Laboratory, Viral Research Division, National Veterinary Research Institute (NVRI), Nigeria. Briefly, 0.5 g of lung, spleen and lymph node from the same animal were pooled together and ground with a mortar and pestle to which sterile sand and phosphate-buffered saline had been added. The 10% suspension was centrifuged at 1800 g for 5 min and the supernatant filtered through a 0.22-µm filter to remove bacterial and fungal contaminants. Nucleic acid was extracted from the filtrate. The remaining unprocessed tissues were stored at -80 °C for future use.
A QIAamp Viral RNA Mini extraction kit® Qiagen (Hilden, Germany) was used to extract total RNA from the field samples and from the positive control, according to the manufacturer’s instructions. The positive control was a live attenuated PPRV Nigeria 75/1 vaccine strain produced at the NVRI, Nigeria (Diallo
The samples were screened by a one-step reverse transcriptase–polymerase chain reaction (RT-PCR) assay for the detection of PPRV nucleic acid using a GeneAmp® PCR System (LifeTech) and the following Verso (Thermo-Scientific®) protocol: 3.5 µL of ultra-pure sterile water, 1.0 µL RT-Enhancer, 1.0 µL (10 pmole) of each forward primer PPR-NP3 (5’-TCTCGGAAATCGCCTCACAGACTG) and reverse primer PPR-NP4 (5’-CCT CCT CCT GGT CCT GGT CCT CCA GAA TCT), 12.5 µL one-step PCR Hot-Start Master Mix (2×), 1.0 µL of enzyme-mix and 5.0 µL of RNA template in a final volume of 25 µL. The PCR cycling conditions consisted of an initial cycle of 50 °C for 15 min, 95 °C for 15 min, 45 cycles of 95 °C for 30 sec, 55 °C for 30 sec, 72 °C for 30 sec and a final extension at 72 °C for 10 min.
The amplified PCR products were analysed by electrophoresis in a 1% Tris acetate–EDTA agarose gel stained with ethidium bromide at a concentration of 1 µg/mL, and run at 120 V for 45 min. The bands were visualised under ultraviolet light and photographed. A 350-basepair (bp) fragment of the N-gene between nucleotides 1232 and 1583 of the N-gene (Couacy-Hyman
The amplicons were purified using a QIAquick® PCR purification kit (Qiagen®, Southern Cross Biotechnology) according to the manufacturer’s instructions, packaged in dry-ice and sent by air from NVRI (Vom, Nigeria) to Inqaba Biotec (South Africa) for sequencing. Amplicons were sequenced directly with a BigDye® Terminator v.3.1 cycle sequencing kit (LifeTech) according to the manufacturer’s instructions. Precipitation of extension products was by the ethanol precipitation protocol of Lifetech®. Samples were electrophoresed using the spectruMedix Genetics analysis system SCE 240.
Sequences were assembled using the Staden package (Staden, Beal & Bonfield
A 243-nucleotide fragment of the PPRV N-gene (between nucleotides 1307–1549 of sequence GenBank accession number L39878) was used for phylogenetic analysis. A general time-reversible model with a gamma-shaped distribution of rate variation across sites (GTR + G) was selected by Akaike Information Criterion in Modeltest v3.7 (Posada & Crandall
Amplicons of the expected 350 bp were obtained by RT-PCR (
Positive reverse transcriptase–polymerase chain reaction of the peste-des-petits-ruminants virus N-gene of swab/homogenate samples is indicated by a 350-bp band.
Description of the animals and samples that tested positive for peste-des-petits-ruminants virus by Verso One-Step reverse transcriptase. Tissue samples were pooled.
Sample number | Location | Species | Sex | Age | Sample type | Clinical signs | RT-PCR |
---|---|---|---|---|---|---|---|
003 | Langtang-N | Ovine | F | Adult | NS | D, ND | - |
005 | Jos-North | Caprine | F | Adult | NS | D, ND | - |
006 | Jos-North | Ovine | M | Adult | NS | D, ND | - |
007 | Jos-North | Ovine | M | Adult | NS | ND | - |
012 | Langtang-N | Ovine | F | Adult | L, LN, S | ND | +’ve |
014 | Bassa | Caprine | F | Adult | L, LN, S | D, ND | +’ve |
017 | Barakin Ladi | Caprine | F | Adult | L, LN, S | D, ND | +’ve |
018 | Barakin Ladi | Caprine | F | Adult | L, LN, S | D, ND | +’ve |
052 | Minna | Caprine | M | Adult | L, LN, S | D, ND | - |
053 | Minna | Caprine | M | Adult | L, LN, S | ND | +’ve |
054 | Minna | Caprine | M | Adult | L, LN, S | ND | - |
055 | Minna | Caprine | M | Adult | L, LN, S | ND | - |
058 | Bosso | Caprine | F | Adult | L, LN, S | D, ND | +’ve |
059 | Bosso | Caprine | M | Adult | NS | ND | +’ve |
072 | Sokoto | Ovine | M | Adult | L, LN, S | ND | +’ve |
074 | Sokoto | Ovine | M | Adult | L, LN, S | ND | - |
079 | Sokoto | Caprine | M | Adult | L, LN, S | ND | +’ve |
082 | Kano | Caprine | M | Adult | NS | ND | +’ve |
096 | Kano | Caprine | M | Adult | L, LN, S | D, ND | +’ve |
114 | Kaduna | Caprine | F | Adult | L, LN, S | D, ND | +’ve |
117 | Tudun Wada | Ovine | F | Adult | L, LN, S | ND | - |
118 | Tudun Wada | Caprine | F | Adult | L, LN, S | ND | +’ve |
119 | Tudun Wada | Caprine | M | Adult | L, LN, S | ND | +’ve |
144 | Yola | Caprine | F | Adult | NS | ND | +’ve |
151 | Yola | Caprine | M | Adult | L, LN, S | D, ND | +’ve |
152 | Yola | Caprine | F | Adult | L, LN, S | D, ND | +’ve |
153 | Yola | Caprine | M | Adult | L, LN, S | ND | - |
155 | Yola | Caprine | M | Adult | L, LN, S | ND | - |
156 | Yola | Caprine | M | Adult | L, LN, S | D, ND | - |
162 | Bauchi | Caprine | F | Adult | NS | ND | - |
163 | Bauchi | Caprine | M | Adult | NS | ND | +’ve |
170 | Bauchi | Caprine | M | Adult | NS | ND | +’ve |
175 | Bauchi | Ovine | F | Adult | L, LN, S | D, ND | - |
177 | Bauchi | Caprine | F | Adult | L, LN, S | D, ND | +’ve |
184 | Agege | Caprine | M | Adult | NS | ND | +’ve |
185 | Agege | Caprine | F | Adult | NS | ND | +’ve |
187 | Agege | Ovine | F | Adult | NS | ND | - |
188 | Agege | Ovine | F | Adult | NS | D, ND | - |
192 | Agege | Ovine | F | Adult | L, LN, S | D, ND | +’ve |
205 | Ibadan-N | Caprine | F | Adult | NS | ND | +’ve |
207 | Ibadan-N | Ovine | M | Adult | NS | D, ND | +’ve |
211 | Ibadan-N | Caprine | M | Adult | L, LN, S | D, ND | +’ve |
213 | Ibadan-N | Caprine | M | Adult | L, LN, S | D, ND | +’ve |
218 | Ibadan-N | Ovine | M | Adult | L, LN, S | D, ND | +’ve |
219 | Ibadan-N | Ovine | M | Adult | L, LN, S | D, ND | +’ve |
220 | Ibadan-N | Caprine | M | Adult | L, LN, S | D, ND | - |
230 | Oje-Oba | Caprine | M | Adult | NS | ND | +’ve |
238 | Akure-South | Caprine | F | Adult | L, LN, S | ND | +’ve |
239 | Akure-South | Caprine | M | Adult | L, LN, S | ND | - |
305 | Ikot-Ebom | Caprine | F | Adult | NS | ND | +’ve |
310 | Etaha-Itan | Caprine | F | Adult | NS | D, ND | +’ve |
316 | Etaha-Itan | Caprine | F | Adult | L, LN, S | D, ND | +’ve |
320 | Etaha-Itan | Caprine | F | Adult | L, LN, S | ND | +’ve |
NS, nasal swab; L, lung; LN, lymph node; S, spleen; D, Clinical signs included diarrhoea; ND, nasal discharge; RT-PCR, peste-des-petits-ruminants virus by Verso One-Step reverse transcriptase.
Description of the regions, study areas and period of sample collection, location and numerical number of positives in percentage and total number of samples collected.
Region | State | Location | Tissue | Swab | Total | |||
---|---|---|---|---|---|---|---|---|
Number positive/number collected | % | Number positive/number collected | % | Number positive/number collected | % | |||
North-central (July 2010) | Plateau | Langtang-N | 1/11 | 9 | 0/3 | 0 | 1/14 | 7 |
Barakin Ladi | 2/4 | 50 | 0/1 | 0 | 2/5 | 40 | ||
Jos-North | - | - | 0/3 | 0 | 0/3 | 0 | ||
Bassa | 1/4 | 25 | 0/2 | 0 | 1/6 | 17 | ||
Benue | Makurdi | 0/8 | 0 | 0/11 | 0 | 0/19 | 0 | |
Gboko | 0/1 | 0 | 0/0 | 0 | 0/1 | 0 | ||
Niger | Minna | 1/1 | 100 | 0/10 | 0 | 1/11 | 9 | |
Bosso | 1/9 | 22 | 1/0 | 0 | 2/9 | 22 | ||
North-west (August 2010) | Sokoto | Sokoto | 2/10 | 20 | 0/10 | 0 | 2/20 | 10 |
Kano | Kano | 1/10 | 10 | 1/10 | 10 | 2/20 | 10 | |
Kaduna | Zango | 0/0 | 0 | 0/10 | 0 | 0/10 | 0 | |
Tudun Wada | 3/10 | 30 | 0/0 | 0 | 3/10 | 30 | ||
North-east (September 2010) | Borno | Maiduguri | 0/10 | 0 | 0/10 | 0 | 0/20 | 0 |
Adamawa | Yola | 2/12 | 17 | 1/8 | 13 | 3/20 | 15 | |
Bauchi | Bauchi | 1/10 | 10 | 2/10 | 20 | 3/20 | 15 | |
South-west (October 2010) | Lagos | Agege | 1/11 | 9 | 2/9 | 22 | 3/20 | 15 |
Oyo | Ibadan | 4/10 | 40 | 2/10 | 20 | 6/20 | 30 | |
Ondo | Oje-Oba | 1/3 | 33 | 0/11 | 0 | 1/14 | 7 | |
Akure-South | 1/6 | 17 | 0/0 | 0 | 1/6 | 17 | ||
South-east (November 2010) | Abia | Okwoyi | 0/0 | 0 | 0/6 | 0 | 0/6 | 0 |
Umuahia | 0/6 | 0 | 0/8 | 0 | 0/14 | 0 | ||
Imo | Mbaitoli | 0/0 | 0 | 0/11 | 0 | 0/11 | 0 | |
Afor-Nnobi | 0/4 | 0 | 0/0 | 0 | 0/4 | 0 | ||
Orodo | 0/5 | 0 | 0/0 | 0 | 0/5 | 0 | ||
Enugu | Emenne | 0/10 | 0 | 0/10 | 0 | 0/20 | 0 | |
South-south (January 2011) | Akwa-Ibom | Ikot-Ebom | 0/0 | 0 | 1/3 | 30 | 1/3 | 30 |
Etaha-Itan | 2/9 | 22 | 1/8 | 13 | 3/17 | 18 | ||
Cross-Rivers | Akamkpa | 0/0 | 0 | 0/7 | 0 | 0/7 | 0 | |
Calabar | 0/9 | 0 | 0/4 | 0 | 0/13 | 0 | ||
Bayelsa | Sagbama | 0/4 | 0 | 0/16 | 0 | 0/20 | 0 | |
National Center for Biotechnology Information
Number Sequence name | Accession number |
---|---|
1. NG 0Y 2013 00213 |
KF908036 |
2. NG PL 2010 00018 |
KF908037 |
3. NG SO 2010 00079 | KF908037 |
4. NG OY 2013 00205 | KF908037 |
5. NG ON 2010 00230 |
KF908038 |
6. NG VACNVRI75/1 | KF908038 |
7. NG SO 2010 00072 |
KF908039 |
8. NG PL 2010 00014 | KF908039 |
9. NG PL 2010 00017 | KF908039 |
10. NG BA 2013 00177 | KF908039 |
11. NG OY 2013 00207 | KF908039 |
12. NG KN 2010 00096 |
KF908040 |
13. NG AD 2010 00151 | KF908040 |
14. NG BA 2013 00170 |
KF908041 |
15. NG KD 2010 00119 | KF908041 |
16. NG LA 2010 00184 |
KF908042 |
17. NG KD 2010 00118 | KF908042 |
18. NG AD 2010 00152 | KF908042 |
19. NG BA 2010 00163 | KF908042 |
20. NG NI 2010 00058 |
KF908043 |
21. NG OY 2013 00211 |
KF908044 |
22. NG PL 2010 00012 |
KF908045 |
23. NG OY 2010 00218 |
KF908046 |
24. NG LA 2010 00185 | KF908046 |
25. NG LA 2010 00192 | KF908046 |
26. NG OY 2010 00219 | KF908046 |
27. NG AK 2010 00316 | KF908046 |
28. NG AK 2013 00320 | KF908046 |
29. NG AK 2013 00310 |
KF908047 |
Sequences without an asterisk (*) indicate those sequences that were identical to another sequence submitted to GenBank.
An unrooted bootstrapped 50% majority-rule consensus cladogram was produced. The sequences from Oman Ibri and Ethiopia of lineage III grouped together (bootstrap value 100%). Sequences from Côte d’Ivoire, Senegal and Burkina Faso grouped together in lineage I (bootstrap value 100%). The next clade consisted of Nigeria 75/1, Ghana 78 and Mali sequences in lineage II (bootstrap value 97%). The tree branched to lineage IV, which consisted of Indian and Israeli sequences (bootstrap value 88%) (
Fifty percent majority-rule consensus cladogram of partial unrooted peste-des-petits-ruminants virus N-gene sequences from this study and GenBank. The phylogeny was determined by distance analysis in Phylogenetic Analysis Using Parsimony.
The genetic distances, mean and standard deviation calculated between the Nigerian PPRV strains and the GenBank Nigerian strains are summarised in
Genetic distances between peste-des-petits-ruminants virus N GenBank Nigerian sequences and the recent Nigerian sequences, using a general time-reversible model with a gamma-shaped distribution of rate variation across sites (GTR + G).
Number | Nigerian sequences | NG VACNVRI751 | DQ840160 75 1Nigeria | DQ840161 75 2 Nigeria | DQ840162 75 3 Nigeria | DQ840164 76 1 Nigeria | Mean ± standard deviation |
---|---|---|---|---|---|---|---|
1 | NG OY 2013 00213 | 0.0745 | 0.069 | 0.0479 | 0.0523 | 0.0674 | 0.0062 ± 0.0115 |
2 | NG PL 2010 00018 | 0.0805 | 0.0748 | 0.0587 | 0.0633 | 0.0633 | 0.0068 ± 0.0091 |
3 | NG SO 2010 00079 | 0.0805 | 0.0748 | 0.0587 | 0.0633 | 0.0633 | 0.0068 ± 0.0091 |
4 | NG OY 2013 00205 | 0.0805 | 0.0748 | 0.0589 | 0.0633 | 0.0633 | 0.0068 ± 0.0091 |
5 | NG ON 2010 00230 | - | 0.0415 | 0.0398 | 0.0443 | 0.0004 | 0.0032 ± 0.0187 |
6 | NG VACNVRI751 | - | 0.0415 | 0.0398 | 0.0443 | 0.0004 | 0.0032 ± 0.0187 |
7 | NG PL 2010 00017 | 0.0198 | 0.0189 | 0.0164 | 0.0169 | 0.0185 | 0.0181 ± 0.0142 |
8 | NG SO 2010 00072 | 0.0198 | 0.0189 | 0.0164 | 0.0169 | 0.0185 | 0.0181 ± 0.0142 |
9 | NG PL 2010 00014 | 0.0198 | 0.0189 | 0.0164 | 0.0169 | 0.0185 | 0.0181 ± 0.0142 |
10 | NG BA 2013 00177 | 0.0198 | 0.0189 | 0.0164 | 0.0169 | 0.0185 | 0.0181 ± 0.0142 |
11 | NG OY 2013 00207 | 0.0198 | 0.0189 | 0.0164 | 0.0169 | 0.0185 | 0.0181 ± 0.0142 |
12 | NG KN 2010 00096 | 0.0183 | 0.0175 | 0.0015 | 0.0156 | 0.0172 | 0.0167 ± 0.0137 |
13 | NG AD 2010 00151 | 0.0183 | 0.0175 | 0.0015 | 0.0156 | 0.0172 | 0.0167 ± 0.0137 |
14 | NG KD 2010 00119 | 0.0196 | 0.0188 | 0.0174 | 0.0018 | 0.0196 | 0.0187 ± 0.0097 |
15 | NG BA 2013 00170 | 0.0196 | 0.0188 | 0.0174 | 0.0018 | 0.0196 | 0.0187 ± 0.0097 |
16 | NG LA 2010 00184 | 0.0018 | 0.0172 | 0.0147 | 0.0152 | 0.0168 | - |
17 | NG KD 2010 00118 | 0.0018 | 0.0172 | 0.0147 | 0.0152 | 0.0168 | 0.0164 ± 0.0137 |
18 | NG AD 2010 00152 | 0.0018 | 0.0172 | 0.0147 | 0.0152 | 0.0168 | 0.0164 ± 0.0137 |
19 | NG BA 2010 00163 | 0.0018 | 0.0172 | 0.0147 | 0.0152 | 0.0168 | 0.0164 ± 0.0137 |
20 | NG NI 2010 00058 | 0.0173 | 0.0165 | 0.0014 | 0.0146 | 0.0161 | 0.0157 ± 0.0135 |
21 | NG OY 2013 00211 | 0.0186 | 0.0178 | 0.0153 | 0.0158 | 0.0174 | 0.0170 ± 0.0140 |
22 | NG PL 2010 00012 | 0.0173 | 0.0165 | 0.0014 | 0.0146 | 0.0161 | 0.0157 ± 0.0135 |
23 | NG OY 2010 00218 | 0.0183 | 0.0175 | 0.0015 | 0.0156 | 0.0171 | 0.0167 ± 0.0137 |
24 | NG AK 2013 00320 | 0.0183 | 0.0175 | 0.0015 | 0.0156 | 0.0171 | 0.0167 ± 0.0137 |
25 | NG LA 2010 00185 | 0.0183 | 0.0175 | 0.0015 | 0.0156 | 0.0171 | 0.0167 ± 0.0137 |
26 | NG LA 2010 00192 | 0.0183 | 0.0175 | 0.0015 | 0.0156 | 0.0171 | 0.0167 ± 0.0137 |
27 | NG AK 2010 00316 | 0.0183 | 0.0175 | 0.0015 | 0.0156 | 0.0171 | 0.0167 ± 0.0137 |
28 | NG OY 2010 00219 | 0.0183 | 0.0175 | 0.0015 | 0.0156 | 0.0171 | 0.0167 ± 0.0137 |
29 | NG AK 2013 00310 | 0.0184 | 0.0176 | 0.0151 | 0.0157 | 0.0172 | 0.0168 ± 0.0138 |
30 | HQ131921 Soba Khartoum KHSUD08 | 0.0165 | 0.0157 | 0.0133 | 0.0139 | 0.0154 | 0.0150 ± 0.0131 |
31 | KC207871 Pakistan 2012 | 0.0202 | 0.0193 | 0.0167 | 0.0016 | 0.0189 | 0.0182 ± 0.0178 |
32 | DQ840170 88 Guinea | 0.0235 | 0.0226 | 0.0213 | 0.0206 | 0.0235 | 0.0223 ± 0.0131 |
33 | DQ840169 Dorcas86 UAE | 0.0308 | 0.0297 | 0.0281 | 0.0288 | 0.0306 | 0.0296 ± 0.0115 |
The aim of this study was to ascertain whether there were genetic variations between the present strains and previously isolated strains circulating in the country and to determine the geographical lineage(s) of the studied PPRV.
PPR was also known in the past in Nigeria as ‘Kata’ and goat plaque all over the world. In most developing countries including Nigeria, small-ruminant farming covers the basic necessities of the majority of peasants. Sheep and goats are essential sources of subsistence. They improve the survival of the poor people in these countries. Unfortunately, PPR is adversely threatening the production of sheep and goats in endemic areas. PPR is a trans-boundary disease and is part of the group of economically important animal diseases whose outbreaks should be notified to the World Organisation for Animal Health (OIE for International des Epizooties). In Nigeria, because of the high importance of sheep and goats for poor farmers, the control of diseases that have a negative impact on their production is a major goal for programmes aimed at poverty alleviation. Sheep and goats are reared in the same fashion in Nigeria with slight differences between the savannah north and tropical rain forest zone of the south.
The animals are rarely housed or tethered, except in areas such as eastern Nigeria where pressure on land is creating competition between crops and livestock, so the latter must be restrained (Carew
In Nigeria, it has been estimated that sheep and goats provide over 35% of the total animal protein consumed. Their hides support the leather industry and at a conservative off-take value of 600 naira for a small ruminant, the total financial value of the small-ruminant industry in Nigeria could be put at about 40 billion naira, based on an estimated population of 34.45 million goats and 22.09 million sheep (Shamaki 2002). However, disease remains a major limiting factor in their production. The diseases that cause significant deaths in sheep and goats include bacterial and viral pneumonia, parasitic and viral gastro-enteritis, ectoparasitism as well as nutritional and metabolic diseases. Among these, PPR is of paramount significance as a disease entity, as it causes both respiratory and gastro-intestinal tract disorders.
The expected number of 60 samples per zone and 1 PPRV amplicon sequence representation per state with location of sampling mapped by GPS coordinates was achieved across the country except for the riverine Niger Delta of Bayelsa state where movement to villages was difficult because of lack of access roads, and northern states because of the insurgence of the Boko Haram militia. However, sampling was stratified and targeted sheep and goats with classical or sub-clinical signs of fever and depression, ocular and nasal discharges, diarrhoea and emaciation. The sampling was more of a passive surveillance in locations within the study areas, which included the six agro-ecological zones of Nigeria, as indicated in
The 35 positive samples out of a total of 360 (9.7%) samples were from all the agro-ecological zones except the south-eastern zone for which no positive results were obtained by RT-PCR, although some farmers in the zone complained of losing all their goats to an epidemic that resembled PPR prior to sampling. Livestock are not allowed to roam freely in this region, thereby limiting the chances of cross-transmission of the disease from one flock to another during an outbreak. Other possible reasons for the negative results in this area could be because of very low viral load, which could not be detected by the assay, or it could be that the RNA was lost during processing. Previous findings by Wosu
Based on the results in
Fourteen samples collected from the study areas of the north-central region in the month of July, 9 samples from the north-west collected in August, 11 samples from the north-east collected in September, 15 samples from the south-west collected in October, 3 samples from the south-south collected in January tested positive by RT-PCR for PPRV, while none collected from south-east in November tested positive. These findings suggest that PPR was prevalent in Nigeria during the sampled period. However, a study conducted by Wosu
Cattaneo
The genetic similarity and divergence among the present PPRV sequence strains of Nigeria and their relatedness to some of the previously described isolates in GenBank were analysed. The NCBI BLAST search revealed that some Nigerian PPRVs obtained in this study had an identity of 100% for Nigeria 75/1 and 95% for Nigeria 76/1, and unexpectedly most of the strains recently obtained had 97% – 99% identity to strains from the Republic of Gabon (97%) and (96%) identity to strains from the Republic of Iran (96%) (
Nucleotide genetic diversity was examined (
Based on previous studies of geographical distribution of PPRV (Couacy-Hymann
This finding suggests that both lineage II and IV strains of PPRVs are circulating presently in all the studied agro-ecological zones of Nigeria as indicated in
Map of Nigeria describing the GPS location of sampling indicated in red ink and lineages isolated.
The data obtained from this study have provided important and additional information on the molecular epidemiology of PPR virus in Nigeria. However, the clustering of sequences in different areas indicates that the PPRV population in Nigeria is more diverse than previously thought and this study provides a better epidemiological picture of PPRV in endemic areas of the world, such as Nigeria.
The results obtained from this study suggest that PPR still remains endemic with sporadic epidemics in Nigeria and other sub-Saharan African countries. Regular outbreaks in areas where it was considered exotic in the past are conceivably because of an increase in trade and commerce. During this study, molecular characterisation of PPR viruses based on the amplification and sequencing of fragments of the N-gene showed that the PPRV from Nigeria belonged to two different lineages: II and IV, with two sub-clusters in lineage II and two sub-clusters in lineage IV. The new strains were related most closely to isolates from the East African countries of Gabon, Central Republic of Africa and Sudan via Cameroon and Chad. However, there was no clear demarcation that separated where these two different strains were found in Nigeria, but rather both appeared to be found in all the study areas. This suggests that both strains are endemic and circulating all over the country.
Considering the wide distribution of PPR in the world, it would be very helpful to institute an investigative and monitory measure to check the movement of animals from one location to another, especially for countries where PPR is still an exotic disease. PPR should be included in the list of differential diagnoses for pneumo-enteritis in small ruminants in non-endemic countries, and sero-surveillance for PPR in countries bordering endemic and affected countries especially in southern Africa, should be considered.
The authors thank Dr Mohammed S. Ahmed, Executive Director, NVRI Vom, for the financial support. The authors also thank the staff and postgraduate students of the Department of Veterinary Tropical Disease (DVTD), University of Pretoria, South Africa, for their friendship and technical support and the entire staff of NVRI Vom for their moral and technical support.
The authors declare that they have no financial or personal relationships which may have inappropriately influenced them in writing this article.
M.v.V. is the project leader, D.S., M.v.V. and S.M. were responsible for experimental and project design. S.M. performed most of the experiments. M.Q., D.S. and M.v.V. made conceptual contributions. M.Q. performed some of the experiments and calculations. S.M. prepared the samples and did some of the calculations.