Viral genetic diversity, risk factors and socio-economic impact of African swine fever from selected parts of Tanzania, 2019 and 2022
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Date
2022
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Sokoine University of Agriculture
Abstract
African swine fever virus (ASFV) is a double stranded DNA virus of the family Asfaviridae and
genus Asfivirus that causes African swine fever (ASF). The disease can lead up to 100% mortality
of infected domestic pigs causing farmers to incur enormous losses as a result of pig mortalities and
loss of market for pigs and pig products. The disease is one of the major pig diseases in Tanzania,
with outbreaks reported in different regions including Kigoma, Arusha, Dar es Salaam, Dodoma and
Mbeya. Twenty-four (I-XXIV) p72 genotypes have been described so far in Sub-Saharan Africa.
Previous studies have reported ASFV genotypes II, IX, X, XV and XVI to be associated with ASF
outbreaks in Tanzania. Major factors responsible for the spread of ASF in Tanzania include illegal
movement of pigs and swill feeding. This present study was conducted to: (i) diagnose and
genotype ASFV from the 2019 ASF Ngara district outbreak western Tanzania, (ii) genotype
different ASFV trains in ASF outbreaks between march 2021 and march 2022 located un Lake Zone
(Kahama, Geita), northern (Mwanza and Katavi) and central Tanzania (Mpwapwa, Kongwa) and
Morogoro in eastern Tanzania, and to (iii) determine the Ngara ASF outbreak related risk factors
and socio-economic impact.
Spleen, lymph nodes, tonsils and liver were collected from the
outbreaks from pigs with ASF clinical signs including hyperthermia, sternal recumbence and
cutaneous congestion on the limbs, abdomen and outer side of the pinna. Postmortem findings on
affected pigs included splenomegaly, enteritis, and severe hemorrhages of gastrohepatic and
mesenteric lymph nodes. Polymerase chain reaction (PCR) using peste porcina Africana (PPA 1/2)
primers targeting the conserved part of B646L gene (coding for the p72 capsid protein) that
generates a 257 base pairs amplicon was used for ASF diagnosis. Genotyping was done by
nucleotide sequence analysis of the variable 3’ end of the B646L gene. African swine fever was
confirmed in dead pigs by PCR.
Phylogenetic analysis found ASFV genotype II of ASFV in pigs samples from Kongwa
(TAN/2021/Kongwa), Mpwapwa (TAN/2021/Mpwapwa) and Morogoro (TAN/2022/ Morogoro) districts. Genotype X was found in domestic pigs samples from Kahama (TAN/2021/Kahama),
Geita (TAN/2021/Geita) and Katavi (TAN/2022/Katavi) districts and genotype IX was found in
Mwanza (TAN/2022/Mwanza). Phylogenetic analysis clustered ASFV from Ngara into genotype
X. Presence of these genotypes indicate their relation with previous outbreaks in Tanzania
indicating persistent circulation of the viruses. Feeding pigs of uncooked swill was shown to be
significantly associated with the Ngara ASF transmission (OR=3.08, C.I.95%=1.06-8.99,
P=0.0009). Occurrence of ASF outbreak resulted into loss of income and investment as most
farmers kept pigs for the purpose of income generation. Food security was disturbed due to high pig
mortality following occurrence of ASF outbreak. A total of 93 630 000 Tanzanian shillings
(approximately
41 065 USD) was estimated to be lost as a result of pigs’ mortality in 219
households. This calls for the need to educate farmers on the methods for effective control of
disease and for the veterinary services to enforce regulation on movement of pigs and pig products
between regions so as to prevent disease spread.
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Thesis
Keywords
Viral genetic diversity, Socio-economic impact, African swine fever, Tanzania, Asfaviridae genus Asfivirus