Rift Valley Fever in Africa. Kariuki Njenga, DVM, PhD Centers for Disease Control & Prevention, Nairobi, Kenya

Transcription

1 Rift Valley Fever in Africa Kariuki Njenga, DVM, PhD Centers for Disease Control & Prevention, Nairobi, Kenya

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3 Density map of human and animal cases on solonchak soil Legend: Livestock confirmed cases + Sublocations with confirmed human cases Solonchak soils L. Baringo L. Bogoria Munyua et al., Amer J Trop Med Hyg 83 (Supp2), 58-64,2010

4 RVF Disease: Transmission in Livestock Transmitted by infected mosquito bites Various species of mosquito other biting insects can transmit Affects sheep, cattle, camel, goats Abortions bleeding

5 RVF Disease: Transmission in humans o Direct contact with blood, meat, milk and other body fluids of infected animals o Can occur during slaughtering, skinning o Bite of infected mosquito Aerosol transmission? Generated during slaughter of infected livestock

6 What are risk factors of acute RVF in humans? Touching an aborted fetus [OR = 3.83] Consuming or handling products from sick animals [OR = 2.53] Being a herdsman [OR = 1.77] Exposure to mosquitoes was not an independent risk factor Amwayi et al., Amer J Trop Med, 83 (supp2), 14-21, 2010

7 1940 RVF Epidemics ( ) Egypt 1980 Mauritania 1990 Egypt 2000 Egypt Sudan RSA/Comoros 2010 Mauritania KSA/Yemen RSA Madagascar RSA RVF activity in East Africa*

8 Recent Severe Human RVF Outbreaks Year Countries Estimated Cases Reported Cases 1977 Egypt 200,000 18, Mauritania Egypt 1500? 20 Deaths Kenya, Somalia, Tanzania 89,000? Mauritania Mauritania?? KSA, Yemen Egypt Kenya, Tanzania, Somalia? Sudan? , 2009 Madagascar, RSA, Comoros??? 2010,2011 RSA? Data available from Kenya only

9 RVF Risk Mapping: Set up RVF epizootics occur under favorable and persistent eco-climatic conditions Can be mapped either as rainfall or vegetation NDVI integrates all the required conditions Algorithm: Mapping of potential epizootic areas based on literature survey and climate variable thresholding= potential epizootic area mask (PEAM) (C. J. Peters & K.J. Linthicum in Handbook of Zoonoses) NDVI anomaly calculation -- + anomalies > threshold (desert calibration) over 3 month period Persistently + anomalies must have three month mean > 0.1 All pixels that meet this criteria and are within the PEAM are mapped to have conditions necessary for the occurrence of RVF activity

10 Epidemic prediction: Relies on field data Teamwork Capacity Building

11 1 Kenya: RVF Spread Over 52 Last 2 epizootics affected 6 of 8 provinces, 38 of 69 districts Murithi et al., Epi Infect 18, 1-9, 2010

12 Prediction vs. Outbreak Timing: Epi-Curves: Anyamba et al (In Review AJTMH)

13 What is the inter-epizootic period (IEP)? Based on Kenya Dept Vet Svs Data Mean IEP = 3.6 years IEP IEP IEP IEP Murithi et al., Epi Infect 18, 1-9, 2010

14 % of positive samples of species Where is RVF virus maintained? 1. Transovarially in Aedes mosquito spp 2. Endemicity. Cycling between wildlife, livestock and possibly humans within a permissive ecosystem, mediated by the appropriate vectors. In wildlife Cummulative percent of positive samples at each titer level Buffalo Black rhino Other 9 of 17 species tested were positive - Buffalos, Black rhinos, - Thompson gazelles, - Impalas, Elands, Kudus :1280 1:640 1:320 1:160 1:80 Titer level 1:40 1:20 1:10 Evans et al, Epid Inf 8, Negative: Lions, giraffes, common zebras

15 Where is RVF virus maintained? In livestock : Kenya during the IEP Year of birth No. tested Sheep Percentage positive Rostal et al, Amer J Vet Res 71, 522-6, 2010 No. tested Goats Percentage positive Total * 2/75 3

16 Northeastern Province of Kenya December, 1997 December, 2006

17 Sequential Epidemics in Kenya, Somalia, and Tanzania [1997-8; ]

18 Reported Human RVF Cases (Deaths) in Kenya Kirinyaga 5(2) Maragua 4(0) Thika 2(0) Nairobi 5(2) Baringo 174(13) Nakuru 1(1) Kajiado 10(6) ISIOLO 13(0) Wajir 26(12) Garissa 176(59) Ijara 131(27) Tana-River 21(8) Malindi 15(4) Taita-Taveta 15(1) Kilifi 73(20) NEP 333 of 700 (45%) cases Baringo 174 of 700 (24.8%) Cases Kilifi 73 of 700 (10.4%) cases

19 21/11/ /11/ /12/ /12/ /12/ /12/ /01/ /01/ /01/ /01/ /01/ /02/ /02/ /02/ /02/ /03/ /03/ /03/ /03/2007 Cases Confirmed and Probable Rift Valley Fever Cases, Kenya 2006/07(N=340) NEP Kilifi Baringo Alive Dead Date of Onset

20 RVF Outbreaks in Somalia First case confirmed 20 th January, 2007 Total:107 cases, 54 (50.5%) deaths

21 RVF Outbreak in Tanzania First case confirmed Feb 1st, 2007 Total: 309 cases, 144 deaths

22 Sequential Epidemics: How does the virus spread? Epidemic Region 1: Nov 26, 2006 Region 2: Dec 26, 2006 Regions 3,4: Jan 7, 2007 Region 5: Feb 5, 2007 Region 6: Jan 27, 2007 Region 7: Feb 1, 2007 Nderitu et al., J Inf Dis 203, 2011

23 How do epizootics spread? Kenya 2 Kenya 1a Tanzania 1 Kenya 1b Multiple lineages of RVF virus during one epidemic indicate spontaneous activation of resident virus Nderitu et al., J Inf Dis 203, 2011; Bird et al, 2008

24 Number of confirmed RVF cases and deaths by province, South Africa, (latest April 10, 2011) All cases occurred mid-february May each year Province Cases Deaths Eastern Cape Free State Gauteng KwaZulu-Natal Limpopo Mpumalanga Northern Cape North West Western Cape Total Source: NICD, South Africa

25 South Africa: RVF Infection Map, April 2011 Source: NICD, South Africa

26 RVF in Madagascar 1 st Epizootic / Epidemic few cases Another in 1991 Antananarivo # Perinet Forest Epizootic / Epidemic 1990 Epizootic / Epidemic

27 RVF in Madagascar Last cases in March 2009 Primary Forest of Perinet Epizootic / Epidemic 1990 Epizootic / Epidemic 1991 Epizootic / Epidemic 2008 Epizootic / Epidemic Last cases in 2009 Antananarivo # 27

28 Major Interventions (Eastern Africa) Social mobilization Slaughtering ban Major religious holiday (Idd festival) Livestock quarantine Livestock vaccination Vector control (minimal)

29 RVF Outbreak Response 2006 A Step Behind Livestock vaccination Public Education

30 Challenges Poor accessibility: Flooding Timing: Occurred in peak holiday season Limited health services in the region Coordinating surveillance between livestock and human health