Epidemiology of peste des petits ruminants in relation to small ruminants movements and interactions with wildlife in Tanzania
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Date
2021
Authors
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Journal ISSN
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Publisher
Sokoine University of Agriculture
Abstract
Peste des petits ruminants (PPR) is a highly contagious transboundary animal disease of
domestic small ruminants, camels and some wild artiodactyls. It is caused by Small
ruminant morbillivirus (PPRV) of the family Paramyxoviridae classified into four
genetically distinct lineages I, II, III and IV; and shares genetic and antigenic
characteristics with rinderpest (RP) virus. The disease has significant socio-economic
impact on communities which largely depend on livestock for livelihood, and is a threat to
endangered susceptible wild species. This study aimed at investigating the spread and
maintenance of PPR in the pastoral and agropastoral communities characterized by
extensive mobility, in some areas interacting with wildlife, in order to generate necessary
information for proper planning of control and eradication strategies for PPR. A Cross
sectional studies, complimented with review of previous studies were carried out during
the present study. Data collected from livestock and wildlife populations, samples
collected from different agro ecological zones and wildlife from different habitats were
involved in the study. In ecological studies, purposive sampling was performed in sheep
and goats from 32 districts where PPR surveillance had never been carried out after the
confirmation of PPR in Tanzania. The 32 districts involved in the study, included 3
(9.4%), 12 (37.5%) and 17 (53.1%) districts from the coast, semi-arid and plateau
ecological zones, respectively. For epidemiological characterization of PPR, a total of 78
flocks of sheep and goats were investigated from Karatu (n=10), Longido (n=9), Meatu
(n=7), Monduli (n=11), Ngorongoro Conservation Area Authority (NCAA) (n=13),
Ngorongoro (n=18) and Serengeti (n=10).iii
For the investigation of PPR seroprevalence in wildlife from different habitats, four
species of wildlife; buffalos (Syncerus caffer), impalas (Aepyceros melampus), Grant’s
gazelles (Nanger granti) and Thomson’s gazelles (Eudorcas thomsonii) were sampled.
Sample sizes were calculated based on wildlife population obtained from TAWIRI aerial
census
of
2009
and
2010.
PROMESA
software
(http://www.promesa.co
.nz/ProMESA.htm) was used to estimate sample size per location in three types of wildlife
habitats. Habitats were selected based on the level of contacts with wildlife. The habitats
included Serengeti National Park (SNP) - designated only for wildlife, Loliondo Game
Controlled Area (LGCA) - designated for wildlife livestock and other human activities
and Ngorongoro Conservation Area Authority (NCAA) - designated for wildlife and
livestock only. Chemical immobilization technique was used to capture buffalos and
impalas, whereas gazelles were captured by using a modified netting technique, with trap
made using locally available materials. With this technique three vehicles were used to
head the animals towards the trap. All collected samples from livestock and wildlife were
analysed at the SACIDS laboratory of Sokoine University of Agriculture.
On ecological studies, the overall seropositivity across all agro ecological zones based on
c-ELISA was 20.1%, of which 18.8%, 9.4%, 37.5% and 34.4% districts had very high,
high, low and zero PPR seroprevalence respectively. Very high and high seroprevalence
were frequently recorded in the semi-arid districts. Zero and low seroprevalence were
mostly observed in districts from plateaux ecological zone. Statistically there were
significant differences in PPR seroprevalences among districts of different ecological
zones. On PPR outbreak characterization in the Serengeti ecosystem, a total of 160
samples were collected from clinically diagnosed cases, out of which 12 and 11 cases
were confirmed using a lateral flow device (LFD) and real time reverse transcription
polymerase chain reaction (qRT-PCR) tests, respectively. Of the confirmed cases aboutiv
60% of the animals were aged below six months of age with body temperature ranging
from 38.5 to 41.3 o C, about 70% had lacrimation and only 45.5% had diarrhoea. Lineage
III of PPRV was found to be circulating in the area. Semi structured interviews indicated
pastoral communities were aware of PPR syndromes and had traditional names and
remedies unlike in the agropastoral communities who mostly used Swahili terminologies.
There was no clinical case of PPR observed in the 3 different wildlife habitats. However, a
cross sectional survey was conducted to determine the seroprevalence of PPR in wildlife
species. A total of 270 wildlife were captured, 26 (9.6%) from LGCA, 75 (27.8%) from
NCAA and 169 (62.6%) from SNP, out of which two (7.7%), seven (9.3%) and 30
(17.8%) were seropositive, respectively. Results for one (3.8%), six (8%) and 42 (24.8%)
animals from LGCA, NCAA and SNP, respectively, were doubtful. There were no
statistically significant differences in seropositivity between habitats, species, age and sex.
A modified netting technique developed and used during the present study, showed high
animal and operator safety levels with minimal injuries compared to previous techniques.
With this technique it was possible to capture even flighty animals that behave nervously
because of hunting and other human activities, including Thomson’s gazelles (Eudorcas
thomsonii), a species previously found to be difficult to capture by netting. Peste des petits
ruminants was introduced in Tanzania before its confirmation in 2008 in northern
Tanzania and has been spreading into different areas of the country through live animal
trade and pastoralist migration. Seroprevalence of the disease in sheep and goats has been
found to be higher in semi-arid agro-ecological zone. Peste des petits ruminants outbreak
characterization in areas where livestock coexist with wildlife indicated age, temperature
and lacrimation to be important components of the case definition for PPR syndromic
diagnosis. Lineage III was found to be the lineage circulating at the moment in the area.v
Although no clinical cases of PPR were observed in wildlife, PPR antibodies have been
recovered in wildlife coexisting with livestock confirmed to have PPR cases which
indicates that at one point wild animals contracted the virus. There was no statistically
significant difference in the PPR seroprevalence between wildlife coexisting with
livestock and those with no contact with livestock. Therefore, surveillance, prevention,
control and eradication strategies for PPR should consider the agroecological zones
favouring survival and perpetuation of the virus among reservoir hosts and the susceptible
populations in these areas. Pastoral and live animal traders’ movements need to be
considered in planning and implementation of PPR control strategies. Veterinary services
and conservation authorities are encouraged to work together on planning PPR
surveillance and control at different levels. On syndromic diagnosis of PPR in endemic
settings need to consider age, body temperature and lacrimation on case definition. For
species other than sheep and goats the c-ELISA test kits need to be validated as there were
higher levels of doubtful results on laboratory analysis in wildlife samples.
Description
PhD-Thesis
Keywords
Epidemiology, Ruminants, Peste des petits ruminant, Wildlife