Re‐parameterization of a mathematical model of African horse sickness virus using data from a systematic literature search

Abstract

African horse sickness (AHS) is a vector-borne disease transmitted by Culicoides spp., endemic to sub-Saharan Africa. There have been many examples of historic and recent outbreaks in the Middle East, Asia and Europe. However, not much is known about infection dynamics and outbreak potential in these naive populations. In order to better inform a previously published ordinary differential equation model, we performed a systematic literature search to identify studies documenting experimental infection of naive (control) equids in vaccination trials. Data on the time until the onset of viraemia, clinical signs and death after experimental infection of a naive equid and duration of viraemia were extracted. The time to viraemia was 4.6 days and the time to clinical signs was 4.9 days, longer than the previously estimated latent period of 3.7 days. The infectious periods of animals that died/were euthanized or survived were found to be 3.9 and 8.7 days, whereas previous estimations were 4.4 and 6 days, respectively. The case fatality was also found to be higher than previous estimations. The updated parameter values (along with other more recently published estimates from literature) resulted in an increase in the number of host deaths, decrease in the duration of the outbreak and greater prevalence in vectors.

Modelling African horse sickness emergence and transmission in the South African control area using a deterministic metapopulation approach

“…Parameters used in the model. Parameters were informed by the re-parameterised AHS model developed by Fairbanks (2022) [14], the Netherlands AHS model by Backer and Nodelijk (2011) [4] and the bluetongue model by Szmaragd et. al.…”

“…With the gain of this knowledge about infection biology, Backer and Nodelijk (2011) considerably adapted the AHS model by representing midge-tohorse transmission in the Netherlands if an infected horse were to be imported [4]. This vector-host model was then used as a basis for Porphyre and Grewar's model exploring AHS transmission in zebra populations in South Africa [13], and the parameters have recently been further updated following a systematic review [14]. Nevertheless, at the time of this publication, there had not yet been a model which has incorporated the complexities of an equine population where a proportion is vaccinated, nor addressed the potential for spatial spread of infection via midge dispersal.…”

Addressing the recent outbreak of African horse sickness in Lagos, Nigeria

“…Arthropod vectors carry the disease, particularly Culicoides species (biting midges) (3,4). The contagious, fatal, viscerotropic AHS virus can produce an illness marked by fever, vascular leakage, and a high fatality rate (5). ASH differentials are Equine encephalosis, Trypanosomosis, Piroplasmosis, Purpura haemorrhagica, Anthrax, Equine infectious anemia, Equine viral arteritis, and Hendra virus.…”

“…While horses are completely vulnerable to illness, mules and donkeys may be resistant in some cases. In severe outbreaks, horses' mortality rate may surpass 90% rate (5). ASH virus can be studied from unclotted whole blood obtained from affected animals.…”

“…Africa south of the Sahara has an enzootic spread of the illness rate (5). AHS was reported to be rising in South Africa's surveillance zone as of February 2004.…”