Abstract
Peste des petits ruminants virus, which causes a severe disease in sheep and goats, has only recently been officially declared to be present in Tanzania. An epidemiological study was carried out between September 2008 and October 2010 to investigate the incursion, persistence and spread of the virus in Tanzania. The investigation involved serosurveillance, outbreak investigation and computation of epidemiological indices such as the effective reproductive number, persistence and the threshold level for vaccination. Field and molecular epidemiological techniques were applied to isolate, characterise and trace the origin of the virus in Tanzania. A total of 2182 serum samples from goats and 1296 from sheep from 79 villages across 12 districts were investigated. Village-level prevalence of infection was variable (0.00% – 88.00%) and was higher in pastoral than in agro-pastoral villages. The overall antibody response to the virus was 22.10% (CI95% = 20.72% – 23.48%). About 68.00% and 73.00% of seropositive goats and sheep, respectively, did not show clinical signs. The proportion of seropositive animals differed significantly (p ≤ 0.001) between age groups, sex and farming practices. Real-time polymerase chain reaction results showed that the isolated strains belong to lineage III, whose origin is in East Africa and the Middle East. This indicates that one of the northern neighbouring countries is most likely the source of infection. The computed overall effective reproductive number, the threshold level of vaccination necessary to eradicate the disease and persistence were 4.75% and 98.00%, respectively. These estimates indicate that achieving elimination of the peste des petits ruminants virus from pastoral flocks will require significant effort and development of highly effective intervention tools.
Highlights
In Tanzania, sheep and goats are important livestock species as they are able to survive unfavourable climatic conditions of arid and semiarid environments; they are species of choice of pastoralists
The contribution of sheep and goats to food security in Tanzania has recently been threatened by outbreaks of peste des petits ruminants (PPR)
Incursion refers to the first confirmed arrival of PPR virus (PPRV) in the country, persistence refers to the obstinate survival of PPRV in sheep and goat populations in spite of vaccination and other biosecurity measures undertaken to eliminate the virus, and spread refers to the movement of PPRV between different geographical localities
Summary
In Tanzania, sheep and goats are important livestock species as they are able to survive unfavourable climatic conditions of arid and semiarid environments; they are species of choice of pastoralists. These animals are widely distributed across different agro-ecological zones and production systems and form an integral part of the livelihood of rural households. Incursion refers to the first confirmed arrival of PPR virus (PPRV) in the country, persistence refers to the obstinate survival of PPRV in sheep and goat populations in spite of vaccination and other biosecurity measures undertaken to eliminate the virus, and spread refers to the movement of PPRV between different geographical localities. The epidemiological data, clinical and pathological features of this outbreak and recovery and identification of PPRV are reported
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