Detection of African swine fever virus in the tissues of asymptomatic pigs in smallholder farming systems along the Kenya–Uganda border: implications for transmission in endemic areas and ASF surveillance in East Africa

Abworo, Edward Okoth; Onzere, Cynthia; Amimo, Joshua O.; Riitho, Victor; Mwangi, Waithaka; Davies, Jocelyn; Blome, Sandra; Bishop, Richard P.

doi:10.1099/jgv.0.000848

Cited by 39 publications

(52 citation statements)

References 28 publications

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“…The asymptomatic pigs in Kenya carried low virulence strains of genotype X (Okoth et al, ), while those of Tanzania were high virulence strains of genotype II (Uttenthal et al, ). Similar to our findings, asymptomatic pigs in Uganda and on the Kenya–Uganda border also carried genotype IX viruses (Abworo et al, ; Atuhaire et al, ). The discovery of ASFV genotype IX virus in asymptomatic pigs is surprising, as ASFV genotype IX isolates are usually highly virulent (Gallardo et al, ; Masembe et al, ; Onzere et al, ).…”

Section: Discussionsupporting

confidence: 91%

Symptomatic and asymptomatic cases of African swine fever in Tanzania

Chang’a¹,

Mayenga²,

Settypalli

et al. 2019

Transbound Emerg Dis

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African swine fever (ASF) is an acute, highly contagious and deadly viral haemorrhagic disease of domestic pigs caused by African swine fever virus (ASFV). In ASF endemic countries, there are an increasing number of reports on circulating ASFV strains with different levels of virulence causing a broad range of clinical symptoms in susceptible animals. Tanzania, where ASFV is endemic since 2001, recorded several outbreaks including symptomatic and asymptomatic cases between 2015 and 2017. We collected 35 clinical samples from four outbreaks for diagnostic confirmation and sequenced the partial B646L (p72), the full E183L (p54) gene, the central variable region of the B602L gene and the intergenic region between the I73R and I329L genes to characterize molecularly the new ASFV isolates and analyse their relatedness with previously reported Tanzanian and foreign isolates. We detected ASFV in 21 samples, 15 from symptomatic and six from asymptomatic pigs. Phylogenetic analyses based on the partial p72 gene and the complete p54 (E183L) genes revealed that the ASFVs in samples from symptomatic pigs belonged to genotypes II and those in samples from asymptomatic pigs belonged to genotype IX. The CVR profiles of the p72 genotype II and genotype IX isolates differed between each other and from previously published Tanzanian sequences. The sequence analysis of the intergenic region between the I73R and I329L for the 2017 genotype II isolates showed the absence of one GGAATATATA motif in those isolates. This study showed the simultaneous circulation of two different ASFV genotypes with different levels of pathogenicity in Tanzania. Since the existence of sub‐clinically infected pigs may contribute to the persistence of the virus, our findings suggest continuous surveillance and characterization of ASFV isolates in disease‐endemic regions.

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Section: Discussionsupporting

confidence: 91%

Symptomatic and asymptomatic cases of African swine fever in Tanzania

Chang’a¹,

Mayenga²,

Settypalli

et al. 2019

Transbound Emerg Dis

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“…A high ASFV seroprevalence of 24.2% was found by ELISA assay. Additionally the higher prevalence of ASFV obtained in our study compared to studies conducted in farm level [20] may be due to the fact that farmers probably recognize ASF symptoms at an early stage and rapidly bring animals to the slaughter house for sale [21]. This evidence was supported by a considerably higher ASFV prevalence found in apparently healthy animals sampled at slaughterhouse, than in the farm pig population [22].…”

Section: Discussionsupporting

confidence: 54%

Evidence of African Swine Fever Virus in Pigs Slaughtered at Muhanzi Municipal Abattoir in Bukavu City, Eastern of Democratic Republic of Congo

Patrick¹

2019

IJMB

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African swine fever (ASF) is an acute, highly infectious and fatal arboviral disease affecting both wild and domestic pigs causing a very high mortality rate that goes up to 100%. Up to date no vaccines are available to protect the animals against the disease. No study has been conducted to assess the presence of ASFV in imported slaughtered pigs in Bukavu city and very limited literature is available on ASF in the entire country of Democratic Republic of Congo. A cross sectional study was carried out in Muhanzi municipal abattoir of Bukavu city, eastern Democratic Republic of Congo to investigate the presence of antibodies against African swine fever virus (ASFV) and the viral genome in imported pigs for slaughtering. The commercial enzyme-linked immunosorbent and the conventional polymerase chain reaction assays were used to screen both ASFV antibodies and viral genome respectively. In total 284 pigs were tested out of which 87.3% (248/284) were female adult of more than 1 year old. The majority of them (75.4% (214/284) were imported from Rwanda of which about 62.7% (178/284) of them presented clinical sign such as redness in the skin. Most of them (90.8%) were exotic breed. Out of 284 animals tested, ASFV antibodies were detected in 69 giving an overall seroprevalence of 24.2% from which pigs originated from Idjwi territory were more ASF seropositive (64.2%) compared to the one imported from Rwanda (11.2%). The seropositivity was found to be significantly associated with the breed (OR= 7.4, p<0.05), origin of animals (OR = 14.2, p<0.05) as well as all the observed clinical signs (p<0.05) except nasal discharges and abnormal liver (p>0.05). Additionally, 38 animals out of 284 tested (13.3%) were ASFV PCR positive with high infectivity rate (35.7%) when pigs slaughtered originated from Idjwi territory of the DRC were found to be more infected than the one imported from Rwanda (OR= 8.5, p<0.05). The ASFV PCR positivity was found to be significantly associated with age where young animals (<12 months old) were found to be more infected (OR= 3.6, p<0.05). Similarly, the local breeds were found to be significantly more infected when compared with exotic breed (OR-7.6; p<0.0001). Deliberate policy has to be implemented in order to prevent spread of the disease to pig farms within the region and for saving the pig industry from ASF devastation.

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“…The discovery of a cycle of maintenance and transmission of ASFV between domestic pigs and O. moubata complex ticks in the Mchinji district in Malawi revealed a pig population with improved resistance to the pathogenic effects of ASFV and the ability of the disease to persist without involvement of wild suids (Haresnape & Mamu, ; Haresnape et al., , ). Similarly resistant populations of domestic pigs have been reported in Kenya (Okoth et al., ), along the Kenya/Uganda border on both sides (Abworo et al., ; Thomas et al., ); Mozambique (Penrith et al., ; Penrith, Thomson, Bastos, Phiri, et al., ) and the Eastern Province of Zambia (Simulundu et al., ). The involvement of ticks in these populations has not been documented and requires further investigation.…”

Section: Transmission Routes Of Asfv In Domestic Cyclesmentioning

confidence: 58%

Epidemiology of African swine fever in Africa today: Sylvatic cycle versus socio‐economic imperatives

Penrith

Bastos

Etter

et al. 2019

Transbound Emerg Dis

101

119

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African swine fever (ASF) is believed to have evolved in eastern and southern Africa in a sylvatic cycle between common warthogs (Phacochoerus africanus) and argasid ticks of the Ornithodoros moubata complex that live in their burrows. The involvement of warthogs and possibly other wild suids in the maintenance of ASF virus means that the infection cannot be eradicated from Africa, but only prevented and controlled in domestic pig populations. Historically, outbreaks of ASF in domestic pigs in Africa were almost invariably linked to the presence of warthogs, but subsequent investigations of the disease in pigs revealed the presence of another cycle involving domestic pigs and ticks, with a third cycle becoming apparent when the disease expanded into West Africa where the sylvatic cycle is not present. The increase in ASF outbreaks that has accompanied the exponential growth of the African pig population over the last three decades has heralded a shift in the epidemiology of ASF in Africa, and the growing importance of the pig husbandry and trade in the maintenance and spread of ASF. This review, which focuses on the ASF situation between 1989 and 2017, suggests a minor role for wild suids compared with the domestic cycle, driven by socio‐economic factors that determine the ability of producers to implement the control measures needed for better management of ASF in Africa.

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Detection of African swine fever virus in the tissues of asymptomatic pigs in smallholder farming systems along the Kenya–Uganda border: implications for transmission in endemic areas and ASF surveillance in East Africa

Cited by 39 publications

References 28 publications

Symptomatic and asymptomatic cases of African swine fever in Tanzania

Symptomatic and asymptomatic cases of African swine fever in Tanzania

Evidence of African Swine Fever Virus in Pigs Slaughtered at Muhanzi Municipal Abattoir in Bukavu City, Eastern of Democratic Republic of Congo

Epidemiology of African swine fever in Africa today: Sylvatic cycle versus socio‐economic imperatives

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