Characterisation of Peste Des Petits Ruminants Disease in Pastoralist Flocks in Ngorongoro District of Northern Tanzania and Bluetongue Virus Co-Infection

Abstract

Peste des petits ruminants (PPR) disease was first confirmed in Tanzania in 2008 in sheep and goats in Ngorongoro District, northern Tanzania, and is now endemic in this area. This study aimed to characterise PPR disease in pastoralist small ruminant flocks in Ngorongoro District. During June 2015, 33 PPR-like disease reports were investigated in different parts of the district, using semi-structured interviews, clinical examinations, PPR virus rapid detection test (PPRV-RDT), and laboratory analysis. Ten flocks were confirmed as PPRV infected by PPRV-RDT and/or real-time reverse transcription-polymerase chain reaction (RT-qPCR), and two flocks were co-infected with bluetongue virus (BTV), confirmed by RT-qPCR. Phylogenetic analysis of six partial N gene sequences showed that the PPR viruses clustered with recent lineage III Tanzanian viruses, and grouped with Ugandan, Kenyan and Democratic Republic of Congo isolates. No PPR-like disease was reported in wildlife. There was considerable variation in clinical syndromes between flocks: some showed a full range of PPR signs, while others were predominantly respiratory, diarrhoea, or oro-nasal syndromes, which were associated with different local disease names (olodua-a term for rinderpest, olkipiei-lung disease, oloirobi-fever, enkorotik-diarrhoea). BTV co-infection was associated with severe oro-nasal lesions. This clinical variability makes the field diagnosis of PPR challenging, highlighting the importance of access to pen-side antigen tests and multiplex assays to support improved surveillance and targeting of control activities for PPR eradication.

Keywords: PPR; differential diagnosis; ethno-veterinary knowledge; goats; outbreak investigation; sheep; surveillance.

Figure 1

Map of Tanzania. Source: Map data © 2020 Google. The black rectangle indicates the study area in Ngorongoro District in Tanzania, which is shown in more detail in Figure 2.

Figure 2

Map of Ngorongoro District showing the location of the flocks where outbreak investigations were carried out. Outbreak locations are represented by coloured circles and the flock number; red = PPRV disease confirmed; pink = PPRV disease suspected due to proximity to confirmed outbreak and similar clinical signs; grey = other outbreaks investigated but not confirmed as PPR. NCAA = Ngorongoro Conservation Area Authority.

Figure 3

Clinical cases in Flock 1 (confirmed PPRV and bluetongue virus (BTV) infected) in Olorien-Magaiduru ward, showing a range of clinical signs: (a) 1–2-year-old goat with mucoid nasal discharge and (b) diarrhoea—peste des petits ruminants virus (PPRV) rapid diagnostic test (RDT) and PPRV real-time reverse transcription polymerase chain reaction (RT-qPCR) positive; (c) 2–3-month-old goat with lacrimation, nasal discharge, peri-oral skin lesions and (d) mouth lesions—not tested; (e) 8-month-old sheep with nasal discharge, swollen and ulcerated muzzle and ulceration inside lips and tongue—PPRV-RDT and PPRV RT-qPCR negative; (f) 1-year-old goat with peri-oral skin lesions—not tested.

Figure 4

Prevalence of clinical signs in Flocks 1 and 3. (a) Prevalence of type of clinical sign in each species in Flock 1 and (b) Flock 3; lacrim. = lacrimation, nasal disch. = nasal discharge, oral les. = oral lesions, and peri-oral les. = peri-oral lesions. (c) Number of clinical signs per animal by species in Flock 1 and (d) Flock 3. (e) Prevalence of clinical disease in each age group by species in Flock 1 and (f) Flock 3.

Figure 5

PPR cases in Flock 3 (confirmed PPRV infected) in Olorien-Magaiduru showing a range of clinical signs. (a) A 2-year-old goat (G10) with pyrexia, ocular discharge, mucoid nasal discharge blocking nostrils, and (b) diarrhoea and straining—peste des petits ruminants virus (PPRV) rapid diagnostic test (RDT) and PPRV real-time reverse transcription polymerase chain reaction (RT-qPCR) positive; (c) 3-month-old goat with ocular discharge (eyelids stuck together), nasal discharge, and (d) mouth lesions—not tested; (e) 6-month-old goat (G11) with pyrexia, sub-mandibular oedema, lacrimation, nasal discharge and (f) ulcers on lip margin and necrotic lesion upper gum—PPRV-RDT and PPRV RT-qPCR positive.

Figure 6

(a) A 4-year-old sheep with nasal discharge, frothy salivation, swollen and ulcerated muzzle; (b) extensive ulceration of lips and buccal cavity, and diarrhoea. This sheep was peste des petits ruminants virus (PPRV) real-time reverse transcription polymerase chain reaction (RT-qPCR) negative and bluetongue virus (BTV) RT-qPCR positive. It was in Flock 9 (confirmed PPRV and BTV infected) in Olorien-Magaiduru, in which two other sheep were PPRV RT-qPCR positive.

Figure 7

Neighbour-joining tree constructed on the basis of partial N gene sequences of the peste des petits ruminants virus (PPRV). The tree shows the relationships among the African PPRV isolates. The scale bar indicates nucleotide substitutions per site. The Kimura 2-parameter model with percentage of replicate trees in which the associated taxa clustered together in the 1000 bootstrap replicates is shown next to the branches. The six sequences generated in this study (accession numbers: MT181842-47) are indicated by an asterisk at the end of the taxon name. The taxon name of the sequences retrieved from GenBank contains the accession number followed by the name of the country and the year of isolation.