PPR epidemiology. with a special reference to West Africa. R. Lancelot. June CIRAD, Unit ASTRE. Food safety

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1 PPR epidemiology with a special reference to West Africa R. Lancelot CIRAD, Unit ASTRE June

2 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 2

3 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 3

4 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 4

5 Livestock production systems 25 N 20 N 15 N 10 N Aridity classes Hyper arid Arid Semi arid Dry sub humid Humid 5 N 10 W 0 10 E 20 E Source for the aridity index: Trabucco and Zomer (2009); White et al. (2002) 5

6 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 6

7 Mauritania: serological survey El Arbi et al. (2014) 7

8 Burkina: participatory disease searching 14.5 N Protocol 1 Protocol 2 Protocol 3 Protocol km No PPR ountbreak PPR outbreak 14 N 13.5 N 13 N 12.5 N 3 W 2 W 1 W 0 8

9 Ghana: participatory disease searching No PPR suspicion PPR suspicion No vaccination Vaccine alone Vaccine with support Vaccine with support & dewormer km

10 Guinea: participatory disease searching 10

11 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 11

12 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 12

13 Small ruminant populations 10 W 0 10 E 20 E 25 N Sheep Goats Density (heads/km²) < 1 20 N [1, 2) 15 N [2, 10) [10, 20) 10 N [20, 50) 5 N [50, 100) 0 [100, 250) S 10 W 0 10 E 20 E Small ruminant population size ( 1000 heads): source Robinson et al. (2014); Nicolas et al. (2016) Species arid semi-arid sub-humid humid Total Sheep 30,146 44,554 11,767 9,700 96,167 Goat 34,729 53,965 19,482 23, ,552 13

14 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 14

15 Reminder: R 0 The basic reproduction number R 0 (r nought) of an infection is the number of cases one case generates on average over the course of its infectious period, in an otherwise uninfected population (Anderson and May, 1991) R 0 helps determine whether or not an infectious disease can spread through a population R 0 < 1: the infection will die out in the long run R 0 > 1: the infection will be able to spread in a population In an immunologically naive population with homogeneous mixing, the control effort (immunization rate) needed to stop the spread of a disease is: T = 1 1 R 0 15

16 Reminder: the force of infection The force of infection λ is the rate at which susceptible individuals acquire an infectious disease (Anderson and May, 1991) λ = # of new infections # of susceptible exposed average duration of exposure λ can be calculated for an infectious disease in an endemic state if homogeneous mixing of the population and a rectangular population distribution: λ = 1 A where A is the average age of infection 16

17 Infection force λ and R 0 Estimation from field data Infection rate λ s,a from serological surveys, data split by species and age Mortality and offtake rate from cohort surveys Estimation method for the basic reproduction number: R 0 = L A L lifetime, estimated from age at sampling A age of infection (fonction of λ s,a) 17

18 Infection force λ and R 0 17

19 Infection force λ and R 0 17

20 Infection force λ and R 0 Strong age dependency for the infection rate: independently of species and environment infection rate in adults is one order of magnitude smaller than in offsprings Mauritania: arid environment, Sahelian breeds, R and huge between-species differences Guinea: humid environment, WAD breeds, R and no between-species differences 17

21 Sheep and goats are different w.r.t. PPRV Same villages, northern Senegal, cohort survey in mixed sheep and goats herds Goats Sheep Monthly serological incidence Monthly serological incidence Monthly mean clinical score Monthly mean clinical score Value Value Monthly death probability Monthly death probability

22 Sheep and goats are different w.r.t. PPRV 19

23 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 20

24 General pattern Touré et al. (2012) 21

25 Example of Mauritania and Senegal Apolloni et al. (2018) Data source: surveys implemented by National Vet Services 22

26 Example of Mauritania and Senegal Apolloni et al. (2018) Data source: surveys implemented by National Vet Services 22

27 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 23

28 In this region, nation-wide mass vaccination campaigns - with a strong regional coordination, are needed to stop PPRV transmission 24

29 GCES stages 25

30 Vaccination schemes for the control stage One or two area-wide mass-vaccination campaigns targeting 100% of the eligible population = small ruminants 3 mo One or two area-wide mass-vaccination campaigns targeting the offspring 12 mo Mass-vaccination campaigns Hyper-arid, arid and semi-arid environments : 1 annual round Sub-humid, humid environments: 2 rounds / year 26

31 Modeling for ex ante assessment Initial ideas developed for HPAIV vaccination in poultry (Lesnoff et al., 2009): the post-vaccination immunity decreases mostly because of population turn-over Core component: seasonal population dynamic model used to predict the population turnover Hammami et al. (2016, 2018) 27

32 Contrasted population dynamics patterns 28

33 Sheep population, arid environment One annual vaccination round, varying coverage 29

34 Goat population, sub-humid environment One or two annual vaccination rounds, 60% coverage 30

35 Conclusion for ex ante assessment Interest of partial vaccination? Target of 70% post-vacc immunity rate difficult to reach More realistic to target 60% or 50% (R 0 2) We need Sero-epidemiological and demographic studies, with harmonized protocols, to get accurate R 0 estimates in contrasted agro-ecosystems Animal mobility surveys to Identify PPRV transmission hubs, as well as critical vaccination periods Calibrate transmission models Dynamic PPRV transmission models in heterogeneous population: work in progress 31

36 Outline 1 Epidemiological situation Agro-ecological systems PPR is everywhere, at a fine spatial resolution 2 Drivers of PPR epidemiology Small ruminant density Infection force and R 0 Animal mobility 3 Consequences for vaccination strategy 4 Can it work? 32

37 Average immunity coverage: Ghana 2919 sera in 160 villages Coverage higher for Vaccine alone than for control (p < 10 4 ) Coverage for Vaccine + support higher than for Vaccine alone (p < 10 4 ) No significant difference in coverage for Vaccine + support + deworming and Vaccine + support (p = 0.993) Vaccine + support + dewormer Vaccine + support Vaccine alone Control Seroprevalence rate (%) 33

38 Variations in immunity coverage: Ghana Coverage at the village level Vaccine + support + dewormer Vaccine + support Vaccine alone Control Serological prevalence rate (%) 34

39 Contributions: A. Apolloni, A. Bataille, F. Bouyer, D. Chavernac, C. Coste, A. Diallo, P. Hammami, O. Kwiatek, M. Lesnoff, G. Libeau, M. Peyre, H. Salami (Cirad, OIE/FAO World Reference Laboratory and Collaborating center) G. Mignangou, L. Ouattara, J. Savadogo (Burkina Faso) J. Avuma, S. Ockling (Ghana) L. Kaba (Guinea) A.S. El Arbi, B. El Mamy, K. Isselmou (Mauritania) M. Diop, K. Tounkara (Mali) M. Diop, M. Lo, R. Maboudou, I. Mall, I. Seck, M.T. Seck, D.A. Sow (Senegal) K. Tounkara, D. Bourzat, J. Domenech, A. Dehove (OIE) F. Njeumi, B. Diop, J.J. Soula (FAO) 35

40 References I Anderson, R. and May, R. (1991). Infectious diseases of humans: dynamics and control. Oxford University Press. Apolloni, A., Nicolas, G., Coste, C., El Mamy, A. B., Yahya, B., El Arbi, A. S., Gueya, M. B., Baba, D., Gilbert, M., and Lancelot, R. (2018). Towards the description of livestock mobility in Sahelian Africa: Some results from a survey in Mauritania. PloS one, 13:e El Arbi, A. S., El Mamy, A. B., Salami, H., Isselmou, E., Kwiatek, O., Libeau, G., Kane, Y., and Lancelot, R. (2014). Peste des petits ruminants, Mauritania. Emerg. Infect. Dis., 20(2): Hammami, P., Lancelot, R., Domenech, J., and Lesnoff, M. (2018). Ex-ante assessment of different vaccination-based control schedules against the peste des petits ruminants virus in sub-saharan Africa. PLOS ONE, 13(1):1 20. Hammami, P., Lancelot, R., and Lesnoff, M. (2016). Modelling the dynamics of post-vaccination immunity rate in a population of Sahelian sheep after a vaccination campaign against peste des petits ruminants virus. PLoS One, 11(9):1 24. Lesnoff, M., Peyre, M., Duarte, P. C., Renard, J.-F., and Mariner, J. C. (2009). A simple model for simulating immunity rate dynamics in a tropical free-range poultry population after avian influenza vaccination. Epidemiol. Infect., 137(10):

41 References II Nicolas, G., Robinson, T., Wint, G., Conchedda, G., Cinardi, G., and Gilbert, M. (2016). Using random forest to improve the downscaling of global livestock census data. PLoS One, 11(3):1 16. OIE and FAO (2015). Global strategy for the control and eradication of PPR [Stratégie mondiale pour le contrôle et l éradication de la peste des petits ruminants]. Technical report, OIE, FAO, Paris, Rome. 88 p. Robinson, T., Wint, G., Conchedda, G., Van Boeckel, T., Ercoli, V., Palamara, E., Cinardi, G., D Aietti, L., Hay, S., and Gilbert, M. (2014). Mapping the global distribution of livestock. PLoS One, 9(5):e Touré, I., Ickowicz, A., A.Wane, Garba, I., Gerber, P., Atté, I., Cesaro, J., Diop, A., Djibo, S., Ham, F., Hamadoun, M., Khamis, Y., Niang, I., Saleh, O., Métais, T., Saley, M., Sow, N. A., Toutain, B., and Yahaya, S. (2012). Système d information sur le pastoralisme au Sahel. Atlas des évolutions des systèmes pastoraux au Sahel FAO / CIRAD. Trabucco, A. and Zomer, R. (2009). Global aridity index (global-aridity) and global potential evapo-transpiration (global-pet) geospatial database. CGIAR Consortium for Spatial Information. White, R. P., Tunstall, D. B., and Henninger, N. (2002). An ecosystem approach to drylands: building support for new development policies. World Resources Institute. 37

Costing a PPR Global Strategy

Jonathan Rushton*, Nick Lyons, João Afonso, Alana Bouton *Professor of Animal Health Economics Royal Veterinary College, London, UK Costing a PPR Global Strategy Acknowledgements OIE Bernard Vallat, Joseph