Published Date: 2020-06-21 05:51:25
Subject: PRO/AH> Foot & mouth disease - Sweden: research, airborne transmission
Archive Number: 20200621.7492096
FOOT & MOUTH DISEASE - SWEDEN: RESEARCH, AIRBORNE TRANSMISSION
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Date: Fri 5 Jun 2020 [accessed]
Source: PloS ONE [edited]
Citation: Bjornham O, Sigg R, Burman J. Multilevel model for airborne transmission of foot-and-mouth disease applied to Swedish livestock. PLoS ONE. 2020; 15(5): e0232489. doi: https://doi.org/10.1371/journal.pone.0232489.
The foot and mouth disease is an ever-present hazard to the livestock industry due to the huge economic consequences following an outbreak that necessitates culling of possibly infected animals in vast numbers. The disease is highly contagious, and previous epizootics have shown that it spreads by many routes.
One such route is airborne transmission, which has been investigated in this study by means of a detailed multilevel model that includes all scales of an outbreak. Local spread within an infected farm is described by a stochastic compartment model, while the spread between farms is quantified by atmospheric dispersion simulations using a network representation of the set of farms.
The model was applied to the Swedish livestock industry, and the risk for an epizootic outbreak in Sweden was estimated using the basic reproduction number of each individual livestock-holding farm as the endpoint metric. The study was based on comprehensive official data sets for both the current livestock holdings and regional meteorological conditions.
Three species of farm animals are susceptible to the disease and are present in large numbers: cattle, pigs, and sheep. These species are all included in this study using their individual responses and consequences to the disease.
It was concluded that some parts of southern Sweden are indeed preconditioned to harbor an airborne epizootic, while the sparse farm population of the north renders such events unlikely to occur there. The distribution of the basic reproduction number spans over several orders of magnitudes with low risk of disease spread from the majority of the farms while some farms may act as very strong disease transmitters. The results may serve as basic data in the planning of the national preparedness for this type of event.
[This paper is a timely reminder of airborne transmission of foot and mouth disease virus [FMDV], an extremely highly infectious RNA _Aphthovirus_, member of the Picornaviridae family, the airborne spread of was investigated during the 1967/1968 FMD epizootic in the UK. An outstanding feature, in October 1967, was the spread of the disease in a downwind direction into Cheshire from the primary outbreak near Oswestry. Meteorological evidence for this and earlier epidemics in Great Britain was analysed (1), followed by further research and animal trials (2). It was shown that pigs emit significantly larger amounts of airborne FMDV than cattle and sheep and that the amounts of virus emitted by cattle and sheep are comparable, while the strain of virus markedly influences the amount of airborne virus emitted. Therefore, the major determinants of the quantity of airborne virus emitted from an infected holding and the distance downwind that animals will potentially be at risk are the species affected on the source holding, the number of animals affected, the strain of virus, the weather, and the topography. Models for simulating the airborne spread of FMD have been developed in England, Denmark, France, and Spain. They fall into 2 categories: those designed for predicting spread over short distances (less than 10 km [6.2 mi]) and those predicting spread over distances of up to several hundred kilometres. Long-distance transport of virus in plumes is especially likely across seaways, as the surface turbulence is low and the concentration of airborne particles can be maintained for greater distances than they can over land. The longest distance of airborne FMD spread is believed to be 300 km [186 mi] when, in March 1981, outbreaks in large pig farms in Brittany (northern France) spread infection to cattle on the Isle of Wight, across the Channel (3). The longest recorded distance for spread over land occurred at the start of the 1967 FMD epidemic when disease was spread over 60 km [37 mi].
Airborne spread of the SARS-CoV-2 virus has been subject to discussions and research during the ongoing COVID-19 pandemic, though the distances mentioned, in contrast to those discussed with FMD, range from just centimetres to a few metres rather than kilometres. An interesting investigation, yet under application, involves mink in the Netherlands. - Mod.AS
1. Smith LP, Hugh-Jones ME. The weather factor in foot and mouth disease epidemics. Nature 1969; 223:712-715. doi: https://doi.org/10.1038/223712a0.
2. Donaldson AI, Herniman KAJ, Parker J, Sellers RF. Further investigations on the airborne excretion of foot-and-mouth disease virus. J Hyg. 1970; 68(4): 557-64. doi: 10.1017/s0022172400042480.
3. Donaldson AI, Gloster J, Harvey LD, Deans DH. Use of prediction models to forecast and analyse airborne spread during the foot-and-mouth disease outbreaks in Brittany, Jersey and the Isle of Wight in 1981. Vet Rec.1982; 110(3): 53-7. doi: 10.1136/vr.110.3.53.
HealthMap/ProMED-mail map of Sweden: http://healthmap.org/promed/p/108.]