Rift Valley Fever in Africa Kariuki Njenga, DVM, PhD Centers for Disease Control & Prevention, Nairobi, Kenya
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
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
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
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
1940 RVF Epidemics (1932 2011) 1950 1960 1970 Egypt 1980 Mauritania 1990 Egypt 2000 Egypt Sudan RSA/Comoros 2010 Mauritania KSA/Yemen RSA Madagascar RSA RVF activity in East Africa*
Recent Severe Human RVF Outbreaks Year Countries Estimated Cases Reported Cases 1977 Egypt 200,000 18,000 598 1987 Mauritania 1500 300 224 1993 Egypt 1500? 20 Deaths 1997-98 Kenya, Somalia, Tanzania 89,000? 458 1 1998 Mauritania 300 150 7 1999 Mauritania?? 2 2000 KSA, Yemen 1500 2000 516 1087 87 121 2003 Egypt 300 148 27 2006-07 Kenya, Tanzania, Somalia? 700 309 107 158 144 54 2007 Sudan? 125+ 60+ 2008, 2009 Madagascar, RSA, Comoros??? 2010,2011 RSA? 255 26 1 Data available from Kenya only
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 > 0.025 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
Epidemic prediction: Relies on field data Teamwork Capacity Building
1 Kenya: RVF Spread Over 52 Last 2 epizootics affected 6 of 8 provinces, 38 of 69 districts 1951-1955 1997-2007 10 12 22 21 19 19 2 20 7 20 7 14 16 11 14 16 1 18 11 13 4 18 15 13 8 17 3 9 5 6-6 Murithi et al., Epi Infect 18, 1-9, 2010
Prediction vs. Outbreak Timing: Epi-Curves: 2006-2008 Anyamba et al (In Review AJTMH)
What is the inter-epizootic period (IEP)? Based on Kenya Dept Vet Svs Data 1910-2007 Mean IEP = 3.6 years IEP IEP IEP IEP Murithi et al., Epi Infect 18, 1-9, 2010
% 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 100.00 80.00 60.00 40.00 20.00 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 0.00-20.00 1:1280 1:640 1:320 1:160 1:80 Titer level 1:40 1:20 1:10 Evans et al, Epid Inf 8, 1-92007 Negative: Lions, giraffes, common zebras
Where is RVF virus maintained? In livestock : Kenya during the 1999 2006 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 1999 12 25 5 0 2000 27 11 7 14 2001 17 29 7 0 2002 19 11 10 0 2003 17 18 17 0 2004 29 24 10 10 2005 63 17 15 0 2006 4 0 4 0 Total 188 18* 2/75 3
Northeastern Province of Kenya December, 1997 December, 2006
Sequential Epidemics in Kenya, Somalia, and Tanzania [1997-8; 2006-7]
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
21/11/2006 28/11/2006 05/12/2006 12/12/2006 19/12/2006 26/12/2006 02/01/2007 09/01/2007 16/01/2007 23/01/2007 30/01/2007 06/02/2007 13/02/2007 20/02/2007 27/02/2007 06/03/2007 13/03/2007 20/03/2007 27/03/2007 Cases 20 18 16 14 Confirmed and Probable Rift Valley Fever Cases, Kenya 2006/07(N=340) NEP Kilifi Baringo Alive Dead 12 10 8 6 4 2 0 Date of Onset
RVF Outbreaks in Somalia First case confirmed 20 th January, 2007 Total:107 cases, 54 (50.5%) deaths
RVF Outbreak in Tanzania First case confirmed Feb 1st, 2007 Total: 309 cases, 144 deaths
Sequential Epidemics: How does the virus spread? 2006-2007 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
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
Number of confirmed RVF cases and deaths by province, South Africa, 2010-2011 (latest April 10, 2011) All cases occurred mid-february May each year Province Cases Deaths 2010 2011 2010 2011 Eastern Cape 17 13 1 0 Free State 123 3 11 0 Gauteng 0 0 0 0 KwaZulu-Natal 0 0 0 0 Limpopo 0 0 0 0 Mpumalanga 0 0 0 0 Northern Cape 74 2 11 0 North West 9 0 2 0 Western Cape 4 9 1 0 Total 228 27 26 0 Source: NICD, South Africa
South Africa: RVF Infection Map, April 2011 Source: NICD, South Africa
RVF in Madagascar 1 st Epizootic / Epidemic 1990 -few cases Another in 1991 Antananarivo # Perinet Forest Epizootic / Epidemic 1990 Epizootic / Epidemic 1991 26
RVF in Madagascar Last cases in March 2009 Primary Forest of Perinet Epizootic / Epidemic 1990 Epizootic / Epidemic 1991 Epizootic / Epidemic 2008 Epizootic / Epidemic 2008-2009 Last cases in 2009 Antananarivo # 27
Major Interventions (Eastern Africa) Social mobilization Slaughtering ban Major religious holiday (Idd festival) Livestock quarantine Livestock vaccination Vector control (minimal)
RVF Outbreak Response 2006 A Step Behind Livestock vaccination Public Education
Challenges Poor accessibility: Flooding Timing: Occurred in peak holiday season Limited health services in the region Coordinating surveillance between livestock and human health