Substitution of warthog NF-κB motifs into RELA of domestic pigs is not sufficient to confer resilience to African swine fever virus

Abstract

African swine fever virus (ASFV) causes a lethal, haemorrhagic disease in domestic swine that threatens pig production across the globe. Unlike domestic pigs, warthogs, which are wildlife hosts of the virus, do not succumb to the lethal effects of infection. There are three amino acid differences between the sequence of the warthog and domestic pig ReLA protein; a subunit of the nf-κB transcription factor that plays a key role in regulating the immune response to infections. Domestic pigs with all 3 or 2 of the amino acids from the warthog RELA orthologue have been generated by gene editing. To assess if these variations confer resilience to ASF we established an intranasal challenge model with a moderately virulent ASFV. No difference in clinical, virological or pathological parameters were observed in domestic pigs with the 2 amino acid substitution. Domestic pigs with all 3 amino acids found in warthog RELA were not resilient to ASF but a delay in onset of clinical signs and less viral DNA in blood samples and nasal secretions was observed in some animals. Inclusion of these and additional warthog genetic traits into domestic pigs may be one way to assist in combating the devastating impact of ASFV. African swine fever virus (ASFV) is a large DNA virus and sole member of the family Asfarviridae that causes a mostly lethal haemorrhagic disease, African swine fever (ASF), in domestic pigs and Eurasian wild boar. ASFV can genetically be separated into 24 genotypes that cause the same disease, but immunological cross-protection is limited and poorly understood 1. The introduction of ASF into a country results in trade restrictions and pig losses, thus the disease has a high socioeconomic consequence for both commercial and backyard farmers 2. Accordingly, the spread of this disease is a serious concern for the global pig industry. Following the incursion of a genotype II ASFV into the Caucasus in 2007 the virus has spread through Russia, entered the European Union in 2014 and, in 2018, was detected for the first time in China. Since then the Chinese pig population has declined by at least 20% and ASFV has further spread across many countries in South East Asia 3,4. Combating this global threat is hampered by the lack of a vaccine and is particularly difficult in production systems with poor biosecurity which are more vulnerable to virus introduction and contact with wild suids 1. ASFV infects all members of the family Suidae, which as well as domestic pigs (Sus scrofa domesticus), wild boar (Sus scrofa spp) and others also includes bushpigs (Potamochoerus spp.) and warthogs (Phacochoerus spp.), which are considered natural reservoir hosts 5. In domestic pigs and wild boar acute and subacute forms dominate,

Evaluation of Lesions and Viral Antigen Distribution in Domestic Pigs Inoculated Intranasally with African Swine Fever Virus Ken05/Tk1 (Genotype X)

“…As reported previously [ 35 ], the intranasal inoculation of the Ken05/Tk1 isolate with a dose of 4.4 × 10 4 HAD resulted in the direct infection of 80% of the animals (four out of five pigs). The pigs developed typical acute forms of ASF [ 32 , 37 , 38 ] characterised by short clinical courses (from 5 and 7 days) before reaching the clinical endpoint between day 9 and 12 pi.…”

“…The present study provides detailed pathological data to complement previous studies that evaluated clinical and virological parameters in domestic pigs inoculated intranasally with different doses (high, medium and low) of the ASFV isolate Ken05/Tk1 [ 35 ]. This ASFV isolate was obtained from a tick extracted from a warthog burrow in central Kenya in 2005 [ 36 ].…”

“…As per their viraemia and clinical signs [ 35 ], pigs 83, 84 and 85 were indirectly infected by contact with infected animals after the intranasal inoculation of group B. Clinical signs were first observed at day 13 pi (pig 85), 15 pi (pig 84) and 17 pi (pig 83).…”

With or without a Vaccine—A Review of Complementary and Alternative Approaches to Managing African Swine Fever in Resource-Constrained Smallholder Settings

“…The former approach was used to produce domestic pigs with a warthog RELA orthologue associated with resistance to ASF [ 145 ]. However, challenge with a moderately virulent virus did not protect the pigs from developing fatal ASF [ 146 ]. In contrast, the virus receptor modification approach, although not successful for ASF [ 147 ], was used to breed biologically functional pigs that are fully resistant to porcine reproductive and respiratory syndrome (PPRS) genotypes, using the CRISPR/Cas system to either delete the exon 7 domain of the CD163 gene [ 148 ] or to replace it with the corresponding exon found in the human CD163-like 1 gene [ 149 ].…”

Pig production is at risk from African Swine Fever (ASF) in Nepal

“…All domestic pig breeds and most wild pig species are highly susceptible with the exception of African warthogs ( Phacochoerus africanus ) and bush pigs ( Potamochoerus larvatus ) (McCleary et al., 2020; Netherton, Connell, Benfield, & Dixon, 2019). From its origins in Africa, ASF is now present throughout much of the world other than the Americas, Australia and the New Zealand (OIE, 2020).…”