Practical considerations in the control of a Rift Valley fever epizootic
Practical Considerations in the Control of a Rift Valley Fever Epizootic Presented at OIE Regional Conference Nairobi SAMAYA HOTEL UNITED ARAB EMIRATE by Dr Peter Maina Ithondeka PhD, MBS Director of Veterinary Services, Kenya 14th June 2011
Introduction Rift Valley Fever (RVF) is a viral haemorrhagic disease primarily of cattle, sheep, goats, camels, wildlife and humans Spread: - Aedes mosquitoes, other blood-sucking insects and through skin abrasions Maintenance of virus between outbreaks remains unclear One of the most significant zoonotic disease problems in Africa The haemorrhagic human disease syndrome generates a high degree of panic among the human populations at risk
RVF occurrence in Kenya• A disease fitting RVF description was first described in Kenya in 1912 by Montgomery.• It is believed that the disease might have occurred in 1913 because an outbreak fitting the description of RVF was associated with heavy mortalities of sheep in the Rift Valley (Bres, 1981).• Described as a specific viral entity in 1931• Since then the disease has occurred in 5-15 year cycles – 1926, 1931, 1936, 1944, 1951, 1960/63, 1967/68, 1978/79, 1997/98 and 2006/07• Refer to MS Word tabulation of outbreaks
RVF antibody to virus studies in camels • Study carried out in 1979 after the 1978/79 RVF epizootic in Kenya (Davis, Koros and Mbugua, 1984) • 571 camel sera samples were collected and analysed • 22% of these had high titers of the RVFV neutralizing antibodies
RVF antibody to virus studies in birds –Carried out in 1979 using 171 bird sera (Davies, 1979) –Study was to check if RVF produced viraemia or neutralizing antibodies in birds –Only 3 of Ploceus weavers tested contained specific antibodies to RVF
Role of primates in spread of RVF• To find the natural reservoir to RVF has been the subject of several studies• Smithburn et al.,(1948) failed to detect antibodies in sera from 72 wild monkeys trapped in Uganda in an area where RVFV was isolated in mosquitoes• Pellisier&Rousselet (1954) reported the presence of antibodies in 12 out of 122 monkeys kept in captivity in Brazzaville
Role of primates in spread of RVF(2)• Davies et al.,(1972) failed to detect antibodies from baboon (Papio anubis) in Kenya most of which were from an area where an epizootic of RVF had recently occurred• Davies et al.,(1975) failed to detect antibodies in 1304 velvet monkeys) in Kenya most of which were again from an area where an epizootic of RVF had recently occurred
RVF antibody to virus studies in wildlife Study carried out in 2007 on 896 sera collected from 16 Kenyan wildlife species (Evans et al., 2007) Specimen from 7 species had detectable neutralizing antibodies against RVFV i.e. African buffalo, black rhino, lesser kudu, impala, African elephant, Kongoni and waterbuck.
Number of RVF outbreaks in Kenya from 1912-2002 (5-15 year cycles) 45 40 35No.of outbreaks 30 25 20 15 10 5 0 12 31 51 60 62 64 67 69 71 78 83 89 91 93 98 02 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 20 Year
contingency plans• Preparedness planning, including the development and approval of contingency plans• Prior approval of plans will allow decisions to be made at a political level more rapidly
Response to the 2006/07 RVF outbreak Veterinary department formed a technical committee to advice on control strategy The committee composed of experts from other institutions, development partners, ministry of health and Meteorological department. Departmental management committee for coordination of activities for prevention and control of RVF Zoonotic committee composed of CDC, MOH, FAO, Veterinary Department and WHO
1. Quarantines and slaughter bans Quarantines were imposed in infected districts (livestock movement controls) Livestock slaughterhouses were closed and home slaughters banned Enforcement of quarantine/slaughter bans was through education, use of imams and other law enforcers The quarantine and slaughter bans were lifted based on absence of clinical disease preventive action by moving livestock to high altitude areas to avoid Aedes infested areas
2006/2007 Outbreak: Intervention activities1. Quarantines and slaughter bans2. Surveillance3. Vaccination4. Vector control (insect repellants, sythetic pyrethroids)5. Public education and awareness
2. RVF Surveillance in livestock• Immediately carried out in districts adjacent to the outbreak area to determine the spread• Later extended to areas with known endemic foci - based on – Previous infections – Areas ecologically conducive for vector habitation e.g. thick vegetation cover, swampy and flooded grounds• Veterinary field personnel continuously searched for the disease and collected samples
RVF Surveillance in livestock (2)• In cattle, sheep, goats and camels assessment of titers of anti–RVF virus IgM antibody relative to anti–RVF virus IgG antibody can be used to differentiate recent from historical RVF virus infection.• This is because the duration of detectable anti-RVF IgM antibody in these animals is transient, approximately 60 to 90 days (Bird et al.,2009)
2006/2007 RVF wildlife surveillance• Serum samples collected from buffaloes, Giraffes, warthogs, Elands, Gerenuks• Surveillance done in areas where outbreaks had occurred• Opportunistically during Rinderpest surveillance• In all areas where unusual wildlife deaths were reported
Distribution of sentinel herds to monitor disease # Japata Salabani # # Ngambo # Shantabak # Naivasha Marey ## Sangailu Kotile# # Bachuma N W E S 200 0 200 400 Kilometers
3. Vaccination against RVF• Vaccinations were carried out in goats, sheep, cattle and camels• Started in January 2007 in the North Eastern Province• Later focus shifted to known endemic districts• A total of 2,550,300 doses of RVF vaccine were used in control efforts• Type of vaccine: Smithburn live attenuated vaccine
2006/2007 Outbreak: Vaccinated areas N W E 200 0 200 Kilometers S
4. Vector control• Reduction of vector population using insecticides (pyrethroids) on livestock –- pour- on preparations and spray wash• All herds visited were treated• A total of 5,890 liters of insecticide Pour-on preparation and 632 liters of insecticide spray were used in 14 districts as part of integrated RVF vector control activities.
5. Public awareness and training Press conferences Ministers for Livestock and Fisheries Development and Health DVS on the updates of the disease Radio interviews to educate , inform the public and increase compliance with legal requirements Newspaper advertisements, brochures, radio announcements and television infomercials Training of department field staff on RVF recognition, surveillance and bio- security measures
Impacts of RVF outbreak• Financial losses due to: – Livestock deaths – Abortions – Trade restrictions – Slaughter restrictions• Food insecurity• Decreased demand and prices of meat• Loss of stock
Decision Making Tool for Kenya The department of veterinary services has come up with a contingency plan for RVF outbreaks in Kenya. This plan covers issues such as: RVF preparedness protocols Surveillance protocol (including sentinel herd) Personal protection protocol SOPs for sample collection and storage SOPs for RVF laboratory bio-safety
Contingency plan in RVF control Pre-outbreak protocols Monitoring of weather patterns Passive surveillance Rumor and outbreak investigation Management, maintenance and monitoring of sentinel herds Risk analysis Maintenance of RVF database Outbreak protocols Risk assessment Active surveillance Collection of samples Wildlife surveillance Investigating of disease reports
Decision Making in RVF control (2) RVF simulation protocol Vaccination protocol Vector control protocol Protocol on imposition and management of RVF quarantine measures Protocol for RVF outbreak communication
Phased out decision making• based on using key events as triggers or decision points for partial responses reduce the risk of inappropriate decisions and assure better preparation.• decision-making process involves balancing the lack of perfect information with the need to take a decision to avert losses due to failure to take action.• If the decision is taken too early with scant information, the likelihood of taking a wrong decision is increased and costs will result from inappropriate or unnecessary activities.
Phased out decision making (2)• if a decision is taken too late, the opportunity to intervene effectively may be lost.• Thus, the decision-maker has to balance the risks of over-reacting against those of under-reacting.• effectiveness of phased decision making rests heavily on the trust of its predictive value.
RVF hot spots vaccination strategy• Kenya currently adopts vaccinations in the known RVF hot spots when never the flooding is predicted.• However, it is difficult to gauge the ideal point, in terms of information availability, where a decision should be taken.
Cumulative RVF VaccinationYear Doses• 2007 2,077,000• 2008 1,500,000• 2009 1,199,600• 2010 600,000• Vaccinations have been carried out in RVF outbreak hotspots.
Time lines based on DVS/ILRI 2007 study Risk Factors Cases ResponseRains Vectors Livestock Human Human Vet33.1 days 19.2 days 21 days 35.6 days 12.3 days 68.9 days