Practical Considerations in the Control of a Rift Valley Fever Epizootic

Presented at OIE Regional Conference NairobiSAMAYA HOTEL UNITED ARAB EMIRATE

byDr Peter Maina Ithondeka PhD, MBS

Director of Veterinary Services, Kenya14th 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, Kongoniand waterbuck.

Flooded Dambo North Eastern Province, Kenya

Number of RVF outbreaks in Kenya from 1912-2002 (5-15 year cycles)

0

5

10

15

20

25

30

35

40

45

1912

1931

1951

1960

1962

1964

1967

1969

1971

1978

1983

1989

1991

1993

1998

2002

Year

No

.of

ou

tbreaks

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 activities

1. Quarantines and slaughter bans

2. Surveillance 3. 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 Outbreak: RVF surveillance sites

0 300 Kilometers N

EW

S

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

Ngambo Salabani

Shantabak

Sangailu

Marey

Kotile

Naivasha

Bachuma

200 0 200 400 Kilometers

N

EW

S

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

200 0 200 Kilometers

N

EW

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 decisionpoints for partial responses reduce the risk ofinappropriate decisions and assure betterpreparation.

• decision-making process involves balancing the lackof perfect information with the need to take adecision to avert losses due to failure to take action.

• If the decision is taken too early with scantinformation, the likelihood of taking a wrong decisionis increased and costs will result from inappropriateor 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 Vaccination

Year 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 Response

Rains Vectors Livestock Human Human Vet

33.1 days 19.2 days 21 days 35.6 days 12.3 days 68.9 days

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