Symptomatic and asymptomatic cases of African swine fever in Tanzania.

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.

Validation of a diagnostic tool for the diagnosis of lumpy skin disease.

BACKGROUND: Lumpy skin disease (LSD) is caused by LSD virus which is a member of the Capripoxvirus (CaPV) genus. Although PCR provides for a rapid and sensitive diagnosis, it has limited use due to its complexity in terms of cost, time and equipment. Loop-mediated isothermal amplification (LAMP) is a simple, specific and cost-effective method with a diagnostic accuracy similar to PCR. OBJECTIVES/HYPOTHESIS: To compare the detection rate (DR) of two LAMP assays versus PCR for the detection of CaPV. ANIMALS: This study used 105 apparently health animals (AHA) and 59 clinically sick animals (CSA). METHODS AND MATERIALS: PCR and LAMP assays (LAMP1 and LAMP 2) were compared for detection of CaPV from AHA and CSA using blood and tissue samples. The detection was confirmed by sequencing of PCR positive samples. Analytical sensitivity and specificity of LAMP assays also were assessed. RESULTS: The DR in CSA was 13.6% for PCR whereas for LAMP it was 39.0% and 25.4% for LAMP 1 and 2 methods, respectively. In AHA, the LAMP assay DR was 14.3% and 1.9% for LAMP 1 and 2, respectively. Phylogenetic tree analysis confirmed the identity of CaPV. Analytic sensitivity showed a detection limit of 8 copies/µL. The analytic specificity test showed no cross detection with other infectious agents. CONCLUSION AND CLINICAL IMPORTANCE: Good sensitivity and specificity results for LAMP assay support its application in the routine diagnosis of LSD, whereas its ability to detect LSDV in apparently healthy animals shows its usefulness in identifying populations at risk of LSD.