THE AIRBORNE TRANSMISSION OF FOOT-AND-MOUTH DISEASE (FMD) VIRUSES A contribution to the MATHEPI - project, supported by Austrian Federal Ministry for Health and Women (FMHW) Elisabeth Schachner, Claudia Strele and Franz Rubel Budapest, February 26 th 2004 Working Group Biometeorology, Department for Natural Science, University of Vererinary Medicine, Veterinärplatz 1, A-1210 Vienna
2 Department for Natural Science Topic Outline Motivation and Intentions Method - The Gaussian Spread Model Dispersion Parameters Biological Parameters Example Results Outlook and References
3 Department for Natural Science Motivation and Intentions FMD is a very contagious disease of cloven - hoofed livestock, OIE arranges the FMD on first place of 15 contagious diseases of list A Last outbreak in Europe was in Great Britain, 2001; 4 mill. animals had to be slaughtered, total loss amounts to 6 bill. Euro Since 1963 Austria has been affected by FMD - outbreaks four times (1963, 1966, 1976, 1981); FMD - exercises are provided in the EU, Informationsystems have been set up, which include databases, GIS and model - components; we deliver a contribution to the modelling
4 Department for Natural Science Fig. 1 57 FMD - free countries without vaccination (OIE, July 10 th 2003) Exporting animal products from affected countries or countries with vaccination is nearly impossible!!
5 Department for Natural Science Enviromental Conditions Temperature: Temperatures below 27 C are preconditions for a high survival of the FMD - virus. ph-value: At ph - values below 6.5 the virus gets inactive. (slaughtered animals) Relative Humidity: The viability of the airborne FMD - virus depends principally on the relative humidity (RH) in the atmosphere. Above 55% RH the virus is stable, but below this value it is rapidly inactivated. Under dried, frozen or salted conditions the virus gets preserved.
6 Department for Natural Science Control Strategies Stamping Out: Culling all animals of the confirmed farms Slaughter of Dangerous Contacts: Culling all animals of the surrounding farms
7 Department for Natural Science Transmission direct transmission: smear infection contact infection lactation indirect transmission: active vectors inactive vectors vectorborne - transmission and airborne - transmission
8 Department for Natural Science Theory of the Gauß-Model analysing the transmission of viruses in the atmosphere transport by the wind (advection) and normal to the wind direction (diffusion) the equation for the transport of the concentration is: dc dt = P c Declaration: The concentration C of a substance in an air - volume will be changed by time, if there is a source or a drain Pc for C!
9 Department for Natural Science the equation of the Gaussian - model for a three dimensional continuous source (extracted air of the barn) is: C(x, y, z) = ( Q 2πuσy(x)σz(x) exp y2 2σ y(x) 2 ) (z h)2 2σ z(x) 2 C(x, y, z)... average concentration at distance x,y and z in TCID50 1 /m 3 Q... source or emission rate of FMD - viruses in TCID50/s σy(x), σz(x)... horizontal and vertical dispersion parameter u... average wind speed in m/s 1 50% Tissue Culture Infectious Doses
10 Department for Natural Science the Gaussian normal distribution has the form of a symmetrical exponential function, which argument depends quadratically on x, y and z Concentration of a continuous, in the basic flux emitted source with increasing distance to the source the absolute value of the concentration decreases; at the same time there is a diffusion in y- and z- direction Fig. 2
11 Department for Natural Science Dispersion Parameters σy and σz (ÖNORM M 9440) σy and σz specify the diffusion normal to the wind direction. They depend on the atmospheric conditions (stable, neutral or unstable). we get σy and σz by determining A, B, α and β: σy = B ( x u ) β σz = A ( x u ) α
12 Department for Natural Science values for A, B, α and β: Dispersion numbers Atmosphere β B α A 2 unstable 0.900 1.270 1.456 0.086 3 lightly unstable 0.868 1.105 0.889 0.834 4 neutral 0.835 1.067 0.762 0.900 5 lightly stable 0.796 0.943 0.699 0.640 6 moderate stable 0.799 0.504 0.566 0.737 7 highly stable 0.728 0.458 0.500 0.316 Tabelle 1: A, B, α and β to calculate σy und σz
13 Department for Natural Science Biological Parameters virus emission: Day of clinical Cattle Sheep Swine signs Log10TCID50 2 virus/24h -2 3.4-1 4.6 ±0 3.5 5.1 4.3 +1 4.5 4.0 8.6 +2 5.1 3.2 8.6 +3 4.7 2.7 7.1 +4 4.1 2.4 5.4 Tabelle 2: Amount and duration of the virus emission of different species (Sørensen et al., 2000) 1 50% Tissue Culture Infectious Doses
14 Department for Natural Science amount of the emitted viruses depending on the virusstrain: Virusstrain Emission of MKS - Viruses log10tcid50/24h Cattle Sheep Swine O1 5.06 4.94 7.16 O2 3.86 3.46 6.46 A5 5.27 3.08 7.06 A22 4.16 2.74 5.61 CNoville 4.64 5.06 7.94 CLebanon 4.06 2.86 5.71 durability of the viruses in the atmosphere: The biological half life for RH - values below 55% is about 30 minutes.
15 Department for Natural Science Minimum Infectious Doses (MID): Species MID Inhalation rate C Threshold TCID50/24h m 3 /24h TCID50/m 3 Cattle 10 173 0.06 Swine 400 52 7.70 Sheep 10 9 1.11 Tabelle 3: Minimum Infectious Doses depending on the species (Sørensen et al., 2000) MID and Inhalation rate are known from experiments. C Threshold may be compared with C (x,y,z) from the model result.
16 Concentration Plume Fig. 3 Department for Natural Science Calculated Concentration plume with risk downwind for cattle, sheep and swine (Morris et al., 2002). Note the interchanged colors for pigs and sheep!
17 Department for Natural Science Input - Data for the model geographical data: coordinates of the farms in Styria number of animals listed by species received from the Institute for Applied Statistics and Systemanalysis, Joanneum Research GesmbH (Graz) meteorological data: LM (Local Model) by the DWD (German Weather Service) 100 x 100 m resolution orography 1-48 hours forecast biological data: mentioned on the previous slide
18 Department for Natural Science Geographical location of the farms in Styria Fig. 4 Farms with animals in Styria, total amount 41.227 (Office of the Styrian Government, 2000)
19 Department for Natural Science Example for LM - Data: Humidity for December 1 st 2003 at 1pm Fig. 5 Local Model of the German Weather Service - Humidity, red (high), blue (low).
20 Department for Natural Science Number of emitting animals Range of risk downwind in wind direction Cattle Sheep Swine Swine 6 km 2 km < 0.2 km 1000 Cattle 0.7 km 0.2 km < 0.1 km Sheep 0.7 km 0.2 km < 0.1 km Swine 2 km 0.4 km < 0.1 km 100 Cattle 0.2 km < 0.1 km < 0.1 km Sheep 0.2 km < 0.1 km < 0.1 km Swine 0.5 km 0.1 km < 0.1 km 10 Cattle < 0.1 km < 0.1 km < 0.1 km Sheep < 0.1 km < 0.1 km < 0.1 km Swine < 0.1 km < 0.1 km < 0.1 km 1 Cattle < 0.1 km < 0.1 km < 0.1 km Sheep < 0.1 km < 0.1 km < 0.1 km Tabelle 4: Estimated distance of the airborne spread (Donaldson et al., 2001)
21 Department for Natural Science Outlook visualisation of the plume including the geographical data of the farms application of the Gaussian model to select case - scenarios concept for an Austrian decision support tool
22 Department for Natural Science References DONALDSON et al., 2001: Relative risk of uncontrollable (airborne) of FMD by different species. Online Manuscript, 9pp GARNER M.G. and CANNON R.M., 1995: Potential for windborne spread of FMD virus in Australia. A report prepared for the Australian Meat Research, Corporation, 88pp MORRIS R.S. et al., 2002: Decision - support tools for FMD - control. Rev.sci.tech.Off.int.Epiz., 21(3), 557-567pp SØRENSEN J.H. et al., 2000: An integrated model to predict the atmospheric spread of FMD virus. Epidemiol. Infect., 124, 577-599pp