Odoom, T. | Search bioRxiv

bioRxiv2026

Molecular epidemiology of the globally spreading genetic lineage IV of peste des petits ruminants virus

Peste des petits ruminants (PPR) is a highly contagious viral disease of small ruminants caused by the peste des petits ruminants virus (PPRV), which is classified into four distinct genetic lineages (I-IV). A critical concern in the recent epidemiological history of PPRV is the rapid and widespread expansion of lineage IV (LIV) across West Africa over the past decade. This dominance suggests a potential adaptive advantage of circulating LIV strains in the regions current epidemiological context. In this study, we obtain the genome sequence of 26 new PPRV samples, including historical (pre-2000) and many recent African LIV isolates, offering the first opportunity to investigate the evolutionary history of LIV in Africa and identify genetic events potentially associated with its recent spread. Phylogenomic analyses implemented on a dataset of 167 curated PPRV genome sequences reveal that the most ancestral LIV group comprises strains circulating in Sub-Saharan Africa (designated clade LIVssa), providing robust evidence for an African origin of lineage IV. Our results further indicate that PPRV strains linked to the recent West African expansion of LIV belong to a specific LIVssa subgroup, termed NigB. We identified multiple signatures of selection pressure within the LIVssa sublineage, particularly in the NigB cluster. Several amino acid substitutions unique to LIVssa or NigB were detected, some of which may impact protein function and warrant prioritised investigation. Additional genomic data are required to confirm the association between the NigB group and the ongoing spread of LIV in West Africa. The evolutionary adaptations observed in LIVssa - potentially enhancing transmission efficiency, host range or pathogenicity - could undermine current disease control strategies in regions where PPR poses significant threats to food security and local economies. Author SummaryPeste des petits ruminants virus (PPRV) infects sheep and goats across Africa, Middle East, Asia and Europe, causing disease with major impact on global economy and food security. One genetic lineage of PPRV, called lineage IV (LIV), is at the origin of most recent expansion of the distribution of the disease, including replacement of other lineages in areas of African where PPRV is historically present. Here, we generated genome sequences from PPRV LIV isolates from different dates and places to study the evolution of this genetic lineage and explore whether its recent spread can be associated with the appearance of new mutations in the virus genome. Our results provide evidence that the PPRV LIV originated in Sub-Saharan Africa and identify mutations present only virus isolates currently spready in new regions of Africa. Further research should investigate the impact of these mutations on protein functions and capacity of transmission of PPRV.

evolutionary biology↗

bioRxiv2025

Evaluation of Aggregate Oral Fluid Sampling for Early Detection of African Swine Fever Virus Infection

African swine fever (ASF) is a highly infectious viral disease that poses significant threat to the United States and global pig industries. Given the lack of effective vaccines, control and prevention of the spread of African swine fever virus (ASFV) is dependent on enhanced surveillance and early disease detection. Commercial swine operations in the US are characterized by comparatively large number of pigs, and sampling individual pigs, which represents the main strategy for current ASF surveillance, is both costly and labor intensive. The major objective of this study was to estimate the diagnostic sensitivity of pen-based aggregate oral fluid testing for ASFV in infected pigs in a pen of 30 animals and evaluate its utility as a tool to support surveillance of ASF in the United States. The study was performed in three phases: (i) Virus (Ghana ASFV24) amplification in a target host species to generate the challenge inoculum, (ii) Titration of the inoculum (10% spleen homogenate) in target host species to determine the minimum dose inducing acute ASF in pigs with survival up to 5 - 6 days post-inoculation (dpi), and (iii) The main study involving 186 pigs consisting of 6 replicates of 30 pigs per pen and one seeder pig inoculated with the Ghana ASFV24 per pen. Daily sampling of aggregate oral fluids, uncoagulated blood, oropharyngeal swabs, fecal and water nipple swabs, and recording of rectal temperatures and clinical observations, was carried out. The seeder pigs were each inoculated intramuscularly with 0.5 ml of the 10% spleen homogenate which induced the desired clinical course of ASF in the pigs with survival of up to 6 dpi. ASFV DNA could be detected in the seeder pigs as early as 1 dpi and 2 dpi in the blood and oropharyngeal swabs, respectively. Transmission of ASFV from the seeder pigs to the contact pig population was detected via positive amplification of ASFV DNA in aggregate oral fluid samples at 3 days post-contact (dpc) in 4 out of 6 pens, and in all 6 pens at 4 dpc. Testing of oropharyngeal swabs and blood samples from individual pigs revealed variable number of ASFV positive pigs between 3 and 5 dpc, with detection of 100% positivity between 6 and 18 dpc, the study endpoint. These findings demonstrate the potential utility of aggregate oral fluid sampling for sensitive and early detection of ASFV incursion into naive swine herds. It also demonstrates that testing of environmental samples from the premises could further enhance overall ASF early detection and surveillance strategy. Author summaryEarly detection of ASFV in swine farms requires robust passive surveillance using sample types and sampling methods that allow sensitive and timely detection. Commercial swine operations in the US or North America are characterized by comparatively large number of pigs, and sampling individual pigs, which represents the current strategy for ASF surveillance, is both costly and labor-intensive. Oral fluid has been shown to be an acceptable sample type for detection of ASFV in individual infected pigs. For the first time on such a scale, we conducted a study enrolling 186 pigs, with daily sampling, in six experimental replicates at 3.2% pen prevalence using a highly virulent ASFV (Ghana ASFV24) to evaluate the utility of aggregate oral fluids for early detection of ASFV. Whole genome sequencing and characterization confirmed grouping of the virus with those in the p72 genotype II cluster. We demonstrate that intramuscular inoculation of the seeder pigs induces acute ASF and transmission to the contact pigs which is detectable in aggregate oral fluids as early as 3 - 4 dpc. We have shown that ASFV DNA detections in aggregate oral fluids correlate with the oropharyngeal swabs of individual pigs. In comparison, ASFV DNA in individual blood samples is detected 1-3 days later. The study demonstrates the potential utility of aggregate oral fluid sampling for enhanced surveillance of ASFV in large commercial swine operations.

microbiology↗