Climate change and vector-borne diseases of livestock in the tropics. Peter Van den Bossche

Transcription

1 Climate change and vector-borne diseases of livestock in the tropics Peter Van den Bossche

2 Climate change & animal health Climate change in Africa: Temperature Rainfall Variability

3 Climate change & animal health Direct effects: heat stress Accidents Indirect effects: Quantity and quality of food and water Distribution and prevalence of diseases

4 Vulnerability of Africa to climate change High exposure by heavy reliance on natural resources Limited capacity (financial and technological) to adapt to changing environment

5 Livestock diseases & Climate change Highly contagious diseases: Contact Survival of pathogen Vector-borne diseases: Arboviral diseases transmitted by mosquitoes, midges or biting flies Tsetse-transmitted trypanosomiasis Ticks and tick-borne diseases

6 Vector-borne diseases & Climate change Host Highly dependent environmental factors Vector Pathogen Geographic range Seasonal patterns (seasonality)

7 Tsetse-transmitted trypanosomiasis Season 1,0 0,9 0,8 Rain Cold Hot Miombo A 0,6 0,5 Miombo B 0,7 0,6 0,5 0,4 0,3 Miombo Monthly mean index of abundance 0,4 0,3 0,2 0,1 0,0 0,7 0,6 0,5 0,4 Munga/dambo C 0,2 0,1 0,0 0,5 0,4 0,3 Munga/dambo D Munga 0,3 0,2 0,2 0,1 0,1 0,0 0,0 Dec-90 Jun-91 Dec-91 Jun-92 Dec-90 Jun-91 Dec-91 Jun-92 Spatial Transmission & Disease Month Temporal Month

8 Transmission of vector-borne diseases From: Molyneux (2003) Common themes in vectorborne disease scenarios. Trans. R. Soc. Trop. Med. Parasit., 97,

9 Vector-borne diseases & Climate change What will be the impact of climate change on distribution and transmission of vector-borne diseases in livestock? Predictions are difficult BUT

10 Biological effects of climate change Effects on physiology, metabolism or development rate: Vector ecology and survival Vector competence Pathogen replication Effects on distribution, density and transmission of vector-borne diseases

11 Basic reproductive rate (R 0 ) of infection m mortality Birth R 0 = mbca 2 e -µt µr a m: ratio of vector to host numbers b: transmission coefficient from vertebrate to vector µ c: transmission coefficient from vector to vertebrate a: biting rate of vectors µ: mortality rate of vectors T: incubation period of pathogen in vector r: recovery rate of hosts from infection T Temperature From: de la Rocque et al. (2008) Climate change; effects on animal disease systems and implications for surveillance and control. Rev. Sci. Off. Int. Epiz. 27,

12 Effect on population growth Trypanosomiasis Season Density independent mortality Density dependent mortality Overall mortality Rainy Cold-dry Hot-dry Adult Mean Pupae From: Terblanche, J. S., et al. (2008) Thermal tolerance in a south-east African population of the tsetse fly Glossina pallidipes (Diptera, Glossinidae): Implications for forecasting climate change impacts. Journal of Insect Physiology, 54: From: Phelps, R. J. & Burrows, P. M Prediction of pupal duration of Glossina morsitans orientalis Vanderplank under field conditions. Journal of Applied Ecology, 6: Total Male flies Female flies

13 From: AU/IBAR

14 Effect on development cycle Rift Valley Fever Mosquito-borne Transovarial transmission (Aedes) Drought resistant dormant eggs Flooding

15 Exessive rainfall - El Niño

16 Effect on pathogen development Immunopeptide expression levels in Gmmin the cool and hot seasons Trypanosomiasis Normalized expression levels Cool season Attacin 1 Attacin 2 Defensin Cecropin Hot season Proportion of infected G. m. morsitans (%) Infection rate Fat level 3,2 3,0 2,8 2,6 2,4 2,2 2,0 1,8 Monthly average fat level (mg) , Month

17 Effect on pathogen development Bluetongue 32 C 27 C 21 C 15 C From: Bradley et al. (1995) Effects of temperature on virogenesis of bluetongue virus serotype 11 in Culicoides variipennis sonorensis. Med. Vet. Entomol., 9,

18 Climate change & Transmission of Vectorborne diseases Potential effects of changing climate on transmission But, transmission is multifactorial Real effects difficult to predict