Rift Valley Fever RVF

Enhancing Safe Inter-Regional Livestock Trade

Dubai, United Arab EmiratesJune 13-16, 2011

Definition• Rift valley fever (RVF) is an acute

febrile arthropod-borne zoonotic

disease. It is characterized by high

rates of abortion and neonatal mortality

in sheep, goats and cattle. It causes

hemorrhagic fever, encephalitis,

blindness and sever liver damage in

man.

Rift Valley - Kenya, Africa

• 1900’s: First recognized in sheep

• 1930: Agent isolated

• Intermittent outbreaks in Kenya

–1950-51, major epizootic

• 500,000 sheep abortions

• 100,000 sheep deaths

1978-1977Egypt:

• Humans

– 18,000 cases

– 598 deaths• Encephalitis and hemorrhagic

fever

• Case-fatality less than 1%

• Ruminants

– Abortions and deaths• Sheep, cattle, goats

• Water buffalo, and camels

Other Important Outbreaks

• 1987: Senegal, Africa– Differed from other outbreaks

• Not associated with rainfall

• 1997-98: Kenya, Africa– Largest outbreak reported

– 89,000 humans cases - 478 deaths

• 2000-01: Saudi Arabia and Yemen– First outbreak outside of Africa

• 2003: Egypt– 45 cases; 17 deaths; All cases were

Egyptian farmers

• Transmission

• Arthropod vector

–Mosquitoes

• Aedes

• Anopheles

• Culex

• Others

• Biting flies possible vectors

Other Modes of Transmission

• Direct contact or Aerosol

– Tissues or body fluids of infected animals

• Aborted fetuses . During slaughtering and necropsy

– High levels of virus in blood

• Aerosol

• Amplify virus

– Infect other mosquitoes

– Establish disease in environment

– May lead to large outbreaks

• No person-to-person transmission

– Humans are a possible source of virus for

mosquitoes

Reservoir

• Mosquitoes – Aedes species– Transovarial transmission

– Eggs dormant in soil

for long periods

– Heavy rainfall, eggs hatch

• Ruminant amplifying host

• Secondary vectors can be infected– Culex and Anopheles mosquito species

– Biting flies: midges, phlebotomids, stomoxids.

Amplifying Hosts

• Infected livestock

• High levels of viremia

• Amplifying

– Sufficient to infect mosquito vectors

– Establishes disease in environment

– Leads to large epizootic epidemics

• Humans

– Viremia enough to amplify

• Animals and Rift Valley Fever

Sheep and Goats

• Incubation period: less than 3 days

–High rate of abortion (5-100%)

• Any stage of gestation

– Asymptomatic

–Foul diarrhea, icterus, mucopurulent

nasal discharge

–Acute death (20-30%).

Lambs and Kids

• Incubation period: 12-36 hrs

• Newborn deaths

– High fever, listless, anorexia

– Death - 12 hours to 2 days

– Less than 1 week old

• Mortality >90%

• Lambs and kids over 2 weeks old

– Mortality over 20%

Cattle

• Adults

– Fever, weakness, anorexia, ptyalism,

fetid diarrhea, icterus

– Death - Mortality 10%

– Abortion can be up to 100%

• Calves

– Similar signs to lambs and kids

– Mortality 10-70%

• Prevention and Control

Prevention

• Vaccination of ruminants by using attenuatedvirus vaccine prepared from Smith burnstrain which prohibited in pregnant animals

as it causes birth defects and abortions.

• Avoid and control vectors

• Personal protective equipment

– Aborted fetuses, necropsy

• Avoid contact with infected tissuesand blood

• Restrict movement of animals

• Precautions when traveling

Control

• Do not slaughter sick animals

– Bury or burn carcasses during an outbreak

• Personal protective equipment

– Gloves, coveralls, boots, eyewear, mask

• Avoid contact with infected tissues andblood

– Aborted fetuses, necropsy

• Greatest risk to travelers

Control

• Clean animal housing areas

– Wear personal protective equipment

– Remove all organic materials from

surfaces (manure, feed, animal tissue)

– Use soap or detergent with warm water

– Let dry

• Disinfect animal housing areas

– 1 part bleach:10 parts water

Attenuated tissue culture

vaccine

• Vaccination of lambs with

attenuated virus vaccine prepared

from Smith burn strain at age less

than 6 months.

• it is not safe to use for

vaccination of pregnant animals

as it cause abortion.

• Endemic intropical Africa

–Cyclic epidemicsevery 5-20 years

–Abnormally heavy rainfalls

–Peaks in late summer

• Outbreaks

–Saudi Arabia, Yemen, and Egypt

Distribution of Rift

Valley Fever

Saudi Arabia and Yemen

2000-2001

• 683 humans hospitalized

• 95 deaths (13.9% mortality)

• 82.7% male

• Median age: 50 years

• Youngest patient:14 yrs. old

• 76% had close contact with animals

• An epizootic of Rift Valley fever

was identified in southwest

Saudi Arabia following the

confirmation of cases in

humans in the third week of

September 2000. These were

accompanied by human disease

and abortions in the livestock in

the affected villages.

Arabian

Gulf

Control during outbreak

In response to the Rift Valley Disease

“RVD” out break, the Ministry of Agriculture

applied the following measures:

1. Restriction of animal movement in the

affected area which include Gazan, Asir &

Tohamet Makah. Restriction also included a

surveillance Zoon in NAJRAN and Baha

regions.

2. Massive vaccination of all livestock in the

infected area Smith burn attenuated

vaccine.

.

3. Control of mosquito

A- filling of ponds and marshes.

B- Rainwater drainage.

C- Biocontrol bacillus thuringiensis H14.

D- Chemical control pesticides.

Aerial and ground spraying by

mosquito pesticides codified

E-Assess the efficiency of mosquito

control mosquito traps.

Control after the outbreak

After the end of the epidemic the program

continued with the following measures:

• Vaccination of animals at 6 month old.

• Active disease surveillance for suspected

cases in live stock (flocks with abortion

and or early newborn mortalities).

• Clinical and serological testing of

suspected smuggled animals at Al-Twal

quarantine station on the border with

Yemen Republic.

• Regular examination and serological testing

of sentinel herds distributed in different

localities of the infected zone.

• During the rainy season (August-October)

random serum samples from susceptible

animal were examined by both capture

ELISA kits for (IgM) and (IgG) RVF

antibodies for detection of early infection

"IgM" and monitoring the level of immunity

due to vaccination (prevalence study),

• Rt-PCR was also used for RV virus

detection in periodically collected

mosquitoes.

• Restriction of Animal’s movements:

Measures to control the transmission of

infected animals from infected regions to

other regions includes:

- Quarantine of animals for 30 days.

- Animal Marking.

- Testing animal’s serum for antibodies (IgG).

- Vaccination of animals within 7 days.

Post Epidemic Records Shows that

All the reported virus activity “ were Less

than 1%, which considered as a

characteristic features of RVFV epidemiology

in previously infected areas during the inter

epizootic period and prove the maintenance

cycle of the virus infection.

Studies showed no other foci of the

disease in non-infected regions (sentinel

studies)

* For this reason RVF disease control

program continued :

Mainly to increase the level of

animal immunity and increase

awareness of animal breeders

about the importance of

vaccination.