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Rift Valley Fever in Africa           Kariuki Njenga, DVM, PhDCenters for Disease Control & Prevention, Nairobi, Kenya
Density map of human and animal cases onsolonchak soil               Legend:   •   Livestock confirmed cases              ...
RVF Disease: Transmission in Livestock Transmitted by infected mosquito bites  – Various species of mosquito  – other biti...
RVF Disease: Transmission in humans  o Direct contact with blood, meat, milk and other  body fluids of infected animals  o...
What are risk factors of acute RVF in humans?• Touching an aborted fetus [OR = 3.83]• Consuming or handling products from ...
1940                               1950                               1960                               1970RVF activity ...
Recent Severe Human RVF OutbreaksYear                  Countries          Estimated   Reported   Deaths                   ...
RVF Risk Mapping: Set upRVF – epizootics occur under favorable andpersistent eco-climatic conditionsCan be mapped – either...
Epidemic prediction: Relies on field dataTeamworkCapacity Building
Kenya: RVF Spread Over 52Last 2 epizootics affected 6 of 8 provinces, 38 of 69 districts   1951-1955                      ...
Prediction vs. Outbreak Timing: Epi-Curves: 2006 - 2008Anyamba 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      ...
Where is RVF virus maintained ?1. Transovarially in Aedes mosquito spp2. Endemicity. Cycling between wildlife, livestock a...
Where is RVF virus maintained ?In livestock : Kenya during the 1999 – 2006 IEP                             Sheep          ...
Northeastern Province of KenyaDecember, 1997         December, 2006
Sequential Epidemics in Kenya, Somalia, and Tanzania [1997-8; 2006-7]
Reported Human RVF Cases (Deaths) in Kenya                                                                         NEP    ...
Cases                   0                       2                           4                               6             ...
RVF Outbreaks in SomaliaFirst case confirmed 20th January, 2007Total:107 cases, 54(50.5%) deaths
RVF Outbreak in TanzaniaFirst case confirmed Feb 1st, 2007Total: 309 cases, 144 deaths
Sequential Epidemics: How does the virus spread?                                   2006-2007 Epidemic                     ...
How do epizootics spread?Multiple lineages of RVF virus during one epidemic indicate spontaneousactivation of resident vir...
Number of confirmed RVF cases and deaths byprovince, South Africa, 2010- 2011 (latest April 10, 2011)All cases occurred mi...
South Africa: RVF Infection Map, April 2011Source: NICD, South Africa
RVF in Madagascar       1st Epizootic / Epidemic 1990 -few                       cases                                    ...
RVF in Madagascar         Last cases in March 2009                                    AntananarivoPrimary Forest of Perine...
Major Interventions (Eastern Africa) Social mobilization Slaughtering ban  – Major religious holiday (Idd festival) Livest...
RVF Outbreak Response 2006 – A Step BehindLivestock vaccination   Public Education
ChallengesPoor accessibility: FloodingTiming: Occurred in peak holiday seasonLimited health services in the regionCoordina...
Rift Valley fever in Africa
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Rift Valley fever in Africa

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Presentation by Dr Kariuki Njenga of the Centers of Disease Control & Prevention, at the Enhancing Safe Inter-regional Livestock Trade held at Dubai, UAE, 13-16 June 2011.

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Rift Valley fever in Africa

  1. 1. Rift Valley Fever in Africa Kariuki Njenga, DVM, PhDCenters for Disease Control & Prevention, Nairobi, Kenya
  2. 2. Density map of human and animal cases onsolonchak 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
  3. 3. 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
  4. 4. 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 mosquitoAerosol transmission? – Generated during slaughter of infected livestock
  5. 5. 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
  6. 6. 1940 1950 1960 1970RVF activity in East Africa* Egypt 1980 RVF Epidemics (1932 – 2011) Mauritania 1990 Egypt Mauritania 2000 KSA/Yemen Egypt Sudan RSA/Comoros Madagascar 2010 RSA RSA
  7. 7. Recent Severe Human RVF OutbreaksYear Countries Estimated Reported Deaths Cases Cases1977 Egypt 200,000 18,000 5981987 Mauritania 1500 300 2241993 Egypt 1500 ? 201997-98 Kenya, Somalia, 89,000 ? 4581 Tanzania1998 Mauritania 300 150 71999 Mauritania ? ? 22000 KSA, Yemen 1500 516 87 2000 1087 1212003 Egypt 300 148 272006-07 Kenya, Tanzania, ? 700 158 Somalia 309 144 107 542007 Sudan ? 125+ 60+2008, 2009 Madagascar, RSA, ? ? ? Comoros2010,2011 RSA ? 255 261Data available from Kenya only
  8. 8. RVF Risk Mapping: Set upRVF – epizootics occur under favorable andpersistent eco-climatic conditionsCan be mapped – either as rainfall orvegetation – NDVI integrates all the required conditionsAlgorithm: – 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
  9. 9. Epidemic prediction: Relies on field dataTeamworkCapacity Building
  10. 10. Kenya: RVF Spread Over 52Last 2 epizootics affected 6 of 8 provinces, 38 of 69 districts 1951-1955 1997-2007 10 12 21 22 19 19 2 20 7 20 7 14 16 14 16 1 11 18 11 13 4 18 15 13 8 17 3 9 5 6 - 6 Murithi et al., Epi Infect 18, 1-9, 2010
  11. 11. Prediction vs. Outbreak Timing: Epi-Curves: 2006 - 2008Anyamba et al (In Review AJTMH)
  12. 12. 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
  13. 13. Where is RVF virus maintained ?1. Transovarially in Aedes mosquito spp2. 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 9 of 17 species tested 100.00 were positive % of positive samples of 80.00 60.00 - Buffalos, Black rhinos, - Thompson gazelles, species Buffalo 40.00 Black rhino - Impalas, Elands, Kudus Other 20.00 0.00 80 0 0 0 80 40 20 10 64 32 16 -20.00 12 1: 1: 1: 1: 1: 1: 1: 1: Titer level Evans et al, Epid Inf 8, 1-92007 Negative: Lions, giraffes, common zebras
  14. 14. Where is RVF virus maintained ?In livestock : Kenya during the 1999 – 2006 IEP Sheep Goats Year Percentage Percentage of No. tested No. tested positive positive birth 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 Rostal et al, Amer J Vet Res 71, 522-6, 2010
  15. 15. Northeastern Province of KenyaDecember, 1997 December, 2006
  16. 16. Sequential Epidemics in Kenya, Somalia, and Tanzania [1997-8; 2006-7]
  17. 17. Reported Human RVF Cases (Deaths) in Kenya NEP 333 of 700 (45%) Wajir 26(12) cases ISIOLO Baringo 13(0) 174(13) Garissa Baringo Nakuru 176(59) 1(1) 174 of 700 (24.8%) Ijara Cases Kirinyaga 131(27) 5(2) Kajiado Tana-River Maragua 10(6) 21(8) 4(0) Taita-Taveta Malindi 15(4) Kilifi Thika 15(1) 73 of 700 (10.4%) 2(0) Kilifi Nairobi 73(20) cases 5(2)
  18. 18. Cases 0 2 4 6 8 10 12 14 16 18 20 21/11/2006 28/11/2006 05/12/2006 12/12/2006 19/12/2006 NEP 26/12/2006 02/01/2007 09/01/2007 16/01/2007 Kilifi 23/01/2007 30/01/2007Date of Onset 06/02/2007 13/02/2007 Kenya 2006/07(N=340) 20/02/2007 Baringo 27/02/2007 06/03/2007 13/03/2007 Alive Dead 20/03/2007 Confirmed and Probable Rift Valley Fever Cases , 27/03/2007
  19. 19. RVF Outbreaks in SomaliaFirst case confirmed 20th January, 2007Total:107 cases, 54(50.5%) deaths
  20. 20. RVF Outbreak in TanzaniaFirst case confirmed Feb 1st, 2007Total: 309 cases, 144 deaths
  21. 21. 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
  22. 22. How do epizootics spread?Multiple lineages of RVF virus during one epidemic indicate spontaneousactivation of resident virus Kenya 2 Kenya 1b Kenya 1a Tanzania 1 Nderitu et al., J Inf Dis 203, 2011; Bird et al, 2008
  23. 23. Number of confirmed RVF cases and deaths byprovince, South Africa, 2010- 2011 (latest April 10, 2011)All cases occurred mid-February – May each yearProvince Cases Deaths 2010 2011 2010 2011Eastern Cape 17 13 1 0Free State 123 3 11 0Gauteng 0 0 0 0KwaZulu-Natal 0 0 0 0Limpopo 0 0 0 0Mpumalanga 0 0 0 0Northern Cape 74 2 11 0North West 9 0 2 0Western Cape 4 9 1 0Total 228 27 26 0 Source: NICD, South Africa
  24. 24. South Africa: RVF Infection Map, April 2011Source: NICD, South Africa
  25. 25. RVF in Madagascar 1st Epizootic / Epidemic 1990 -few cases Antananarivo Another in 1991 #Perinet ForestEpizootic / Epidemic 1990Epizootic / Epidemic 1991 26
  26. 26. RVF in Madagascar Last cases in March 2009 AntananarivoPrimary Forest of Perinet #Epizootic / Epidemic 1990Epizootic / Epidemic 1991Epizootic / Epidemic 2008Epizootic / Epidemic 2008-2009Last cases in 2009 27
  27. 27. Major Interventions (Eastern Africa) Social mobilization Slaughtering ban – Major religious holiday (Idd festival) Livestock quarantine Livestock vaccination Vector control (minimal)
  28. 28. RVF Outbreak Response 2006 – A Step BehindLivestock vaccination Public Education
  29. 29. ChallengesPoor accessibility: FloodingTiming: Occurred in peak holiday seasonLimited health services in the regionCoordinating surveillance betweenlivestock and human health

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