Evidence brief: How fast can PPRV spread? Analyzing the results of an experimental PPRV infection of goats equipped with Ultra-Wideband sensors

Abstract

Peste des Petits Ruminants (PPR) is a highly contagious disease affecting goats and sheep. The speed and extent of its spread depend on contact patterns and the virus’s intrinsic characteristics. To estimate its propagation speed and the role of inter-individual contacts, we conducted PPR virus transmission experiments in goats that were equipped with Ultra-Wideband (UWB) sensors to continuously track inter-individual distances alongside clinical and virological monitoring. Using Bayesian modeling, we integrated contact data and health status to estimate the basic reproduction number (R0), the incubation period, and the virus transmissibility. The novel integration of distance tracking revealed that animal density in an area critically drives infection risk: the minimum exposure time that is required for a naïve animal to become infected dropped from nearly two days at low density to just four hours at high density. Overall, the derived R0 estimates were 4.3 (95% HDI: 3.1–4.8) for a 5-day infectious period and 8.6 (95% HDI: 6.2–9.6) for a 10-day infectious period. The incubation period was estimated to be around 14.7 days (95% CI 11.6–20.1). The exposure time varies greatly depending on the density, ranging from nearly two days at low density to around four hours at high density. These findings highlight high-density environments, such as conditions in livestock markets, as an important factor of PPRV transmission between animals and the disease spread. Considering the high frequency of animals’ movement on long distances, the high incubation period, about 15 days, might be one of the factors explaining the spread of PPR along long distances from the source of infection. To efficiently control and eradicate PPR, sheep and goats’ movement control must be one of the means to be applied. Our findings, based on a single lineage IV PPRV strain (Senegal 20-GP) evaluated under experimental conditions, suggest that the adequacy of the current 21-day quarantine period, as specified in the World Organization for Animal Health (WOAH) Terrestrial Code, deserves further evaluation and validation under field conditions.

Introduction

Peste des petits ruminants (PPR) is a highly infectious and contagious disease affecting small ruminants. Clinically, it is characterized by fever, congestion of different mucosal membranes, followed by ocular and nasal discharges, then buccal erosive lesions and diarrhea at the late stage with death in some cases. Because of its morbidity rate that can be as high as 80–90% and a mortality rate as high as 50–80% depending on the epidemiological context, PPR is in the list of economically important animal diseases in which outbreaks must be reported to the World Organization for Animal Health (WOAH). The causative agent of this disease is a virus, the PPR Virus (PPRV). It is one of the members of the genus Morbillivirus in the family Paramyxoviridae, along with the rinderpest virus, the causal agent of rinderpest, the cattle and buffaloes disease that was officially eradicated globally in 2011 [1,2]. Because PPR and rinderpest share similar symptoms (ocular and nasal discharges, buccal erosive lesions and diarrhea), PPR was overlooked for a long time in favor of rinderpest. But gene sequence data that were available as of 1994 had showed that PPRV and RPV are distinct viruses but closely related [3]. In fact, looking carefully at the epidemiological history, both diseases have evolved independently [4]. From its historical stronghold endemic region in West Africa, PPR has expanded to most of African countries, except Southern Africa, the Middle and Near East, and most of the Asian countries (from China to Central Asia), and then some European countries [5,6].