Rift Valley Fever RVF Enhancing Safe Inter-Regional Livestock Trade Dubai, United Arab Emirates June 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
Egypt: 1977-1978• 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
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
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• Vaccination of ruminants by using attenuated virus vaccine prepared from Smith burn strain 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 tissues and 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 and blood – 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 in tropical Africa – Cyclic epidemics every 5-20 years – Abnormally heavy rainfalls – Peaks in late summer• Outbreaks – Saudi Arabia, Yemen, and Egypt
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.
Control during outbreakIn response to the Rift Valley Disease“RVD” out break, the Ministry of Agricultureapplied the following measures:1. Restriction of animal movement in theaffected area which include Gazan, Asir &Tohamet Makah. Restriction also included asurveillance Zoon in NAJRAN and Baharegions.2. Massive vaccination of all livestock in theinfected area Smith burn attenuatedvaccine.
3. Control of mosquitoA- filling of ponds and marshes.B- Rainwater drainage.C- Biocontrol bacillus thuringiensis H14.D- Chemical control pesticides. Aerial and ground spraying by mosquito pesticides codifiedE-Assess the efficiency of mosquito control mosquito traps.
Control after the outbreakAfter 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 Lessthan 1%, which considered as acharacteristic features of RVFV epidemiologyin previously infected areas during the interepizootic period and prove the maintenancecycle of the virus infection. Studies showed no other foci of thedisease in non-infected regions (sentinelstudies)
* 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.