Rift Valley Fever Texas A&m university

Rift Valley Fever

• Texas A&M University

• College of Veterinary Medicine

• Jeffrey Musser, DVM, PhD

• Suzanne Burnham, DVM

Special thanks for materials borrowed with permission from presentations by:

• Dr Linda Logan, “Rift Valley Fever” CSU Foreign Animal Disease Training Course, College of Veterinary Medicine and Biomedical Sciences, August 1-5, 2005.

• Professor JAW Coetzer, Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, “Rift Valley Fever” presented at the FEAD course in Knoxville, Tenn. 2005.

Rift Valley Fever

• Rift Valley Fever (RVF) is an arthropod-borne, acute, fever-causing viral disease of sheep, goats, cattle and people.

• RVF causes abortions in sheep, cattle and goats, high mortalities in lambs and kids and generalized disease in man.

Rift Valley Fever

• RVF is reportable to the OIE.

• It is also on the USDA and Department of Health and Human Services (HHS) High Consequence lists.

Rift Valley Fever

• RVF was first observed when European stocks of domestic animals, which are more severely affected than native stock, were introduced to Africa.

Rift Valley

• Rift Valley Fever was first reported at

• Lake Naivasha in Kenya.

• There were many sheep

• abortions and young

• lambs were found

• sick or dead.

Cyclic epidemics

• Periodic Pandemics occur near “Dambos” or Playa lakes

• These are depressions that accumulate water

• 5-15 year cycles following heavy rainfall

• Flooded Dambos allow the Aedes mosquitoes infected with RVF to emerge

Rift Valley Fever

• Generally found in eastern and southern Africa where sheep and cattle are raised

• Most countries of sub-Saharan Africa

• Madagascar

• September 2000 RVF outbreak in Saudi Arabia and Yemen – first outbreak outside of the African continent

Possible modes of spread

• Infected mosquitoes

• Movement of viremic animals

• Windborne movement of vectors

• Contaminated viscera and tissues

Kenya Africa

• Largest outbreak reported in sheep was in 1950-1951

• 100,000 mortality in sheep

• 500,000 abortions in sheep

Kenya 1997-1998

• Largest outbreak recorded for human cases: 89,000 cases - 478 deaths.

• Flooding near

• Garissa, Kenya

RVF outbreak 1997-98

• Nomadic Refugee Camp at Garissa, 1997

Economic effects

• Disease in

• 89,000 farm

• workers,

• animal handlers

• veterinarians

• 50% abortions in

• ruminants

Economic effects

• Countries of the Arabian peninsula ban trade of livestock from Africa

Etiology

• Etiology

• Host range

• Incubation

• Clinical signs

• Transmission

• Diagnosis

• Differential Diagnosis

Etiology

• Family:

• Bunyaviridae

• Genus:

• Phlebovirus

Etiology

• RVF virus is serologically related to other phleboviruses, but can be differentiated by serum neutralization tests.

• Enveloped RNA virus

• There is only one serotype of RVF virus

• However, there is different pathogenicity among strains of RVF virus

Host Range - Zoonosis

• Mainly a disease of sheep

• Goats are somewhat less susceptible

• Native African cattle are less susceptible than the small ruminants

• Humans

Host Range

• Mainly Sheep

• Mortality in lambs under 2 weeks of age reaches 100%

• Mortality in older sheep reaches 30% with

• abortions at 100%

Host Range

• Goats

• Cattle

• Buffalo

Host Range

• Horses – have viremia but are resistant

Host Range

• Domestic dogs and cats - SUSCEPTIBLE

• Swine - resistant

• Birds - refractory, no virus isolation

Host range

• Cattle are less susceptible, some are subclinical; mortality averages 5% with some abortions

• Springbok

• African Buffalo

• Camels (in Egypt)

• Water buffalo in Egypt

Incubation period

• 1-6 days

• 12-36 hours in lambs; will be dead before they can acquire passive immunity

Clinical signs Sheep and Goats

Clinical signs in sheep

• Most severe in young lambs (mortality has high as 90%)

• Encrustation around the muzzle

• Anorexia

• Abortion

• Jaundice

• Weakness

• Death within 36 hours

Lambs, kids:

• Lambs, kids:

• fever (40-42°C),
• anorexia,
• weakness,
• death within 36 hours
• after inoculation.

Lambs:

• Lambs:

• Mortality rate: for animals under 1 week of age - up to 90%; for animals over 1 week of age - up to 20%

Adults: fever (40-41°C), mucopurulent nasal discharge, encrustation of nostrils

• Adults: fever (40-41°C), mucopurulent nasal discharge, encrustation of nostrils

• Vomiting, foul diarrhea

• Acute death may reach

• 20-30% in adults

Calves: fever (40-41°C), depression. Mortality rate: 10-70%

• Calves: fever (40-41°C), depression. Mortality rate: 10-70%
• Adults: fever (40-41°C), excessive salivation, anorexia, weakness, fetid diarrhea, fall in milk yield. Abortion may reach 85% in the herd. Mortality rate is usually less than 10%

Clinical signs in cattle

• Disease most severe in young animals

• Abortion

• Drop in milk production

• Fever of 104-106 °F

• Excess salivation

Clinical signs

• Dogs: Abortions up to 100%, severe disease and death in puppies

• Death in kittens

Relative susceptibility

• Newborn ruminants ++++

• Pregnant ruminants ++++

• Sheep and young cattle +++

• Adult cattle, goats, sheep ++

• Humans ++

• Dogs, cats and camels +

• Pigs -

RVF is primarily transmitted from animal to animal by a mosquito

• RVF is primarily transmitted from animal to animal by a mosquito

• Aedes, Culex, Anopheles, Erehmapodites, Monsosmia

Transmission

• Vertical transmission in mosquitoes is probably important in maintaining RVF in endemic areas

• Trans-ovarial transmission is important in causing epidemics and maintaining the virus

Transmission

• Other arthropods (Stomoxys, midges and tabanids) are able to transmit RVF by mechanical means

Transovarial Transmission

• Mosquito eggs dormant in soil for long period of time

• Hatch with heavy rainfall

Aerosol Transmission

• RVF virus levels very high in body fluids during viremia

• Virus aerosolized during butchering or necropsy of infected animals

• Surgery, autopsy (humans)

• Laboratory workers risk

Village butchers at risk

Human Transmission

• Direct contact most significant for humans

• Humans get RVF from handling tissues, blood, secretions and excretions of infected animals.

Disease in humans

• Incubation 2-6 days

• Inapparent, or flu-like symptoms

• Fever, headache, myalgia, nausea

• Recovery 4-7 days

• Retinopathy, loss of visual acuity

• Mortality ~1%

Clinical Signs in humans

• RVF in humans can be a severe influenza-like disease.

• Damage to retina (can lead to blindness)

• High fever (100-104 °F, 37.8-40°C),

• Muscular pain

• Weakness

• Nausea

• Epigrastric discomfort

• Photophobia

• Hemorrhagic diathesis

Retinopathy

• Occurs in 1-10% of affected humans

• Conjunctivitis

• Photophobia

• Can lead to permanent vision loss

Tentative diagnosis

• Tentative diagnosis

• epidemiological, clinical and pathological features

• Confirmation of diagnosis

• Virus isolation

• liver, spleen and blood

• Antigen capture ELISA

• PCR

• Serology

• CF test
• Virus neutralization
• ELISA
• other

• Histopathology : Immunohistochemistry

Diagnosis

• Sample collection:

• Heparinized blood

• Spleen

• Liver

• Acute and convalescent serum samples

Diagnosis

• Virus isolation in cell culture

• Virus neutralization

• Antigen detection by IF staining

• ELISA

• Polymerase Chain Reaction (PCR)

Clinical Pathology

• Leucopenia

• Increased liver enzymes

• Prolonged clotting time, thrombocytopenia

• Disseminated intravascular coagulopathy

Necropsy findings

• Massive hepatitis: hemorrhages, necrotic foci, marked enlargement, orange-brown, friable, edematous liver tissue

• (“If you open a newborn lamb, the liver jumps into your face” Coetzer)

• Chocolate-brown digested blood in abomasum, hemorrhages in intestinal mucosa, free blood in lumen

Focal or generalized hepatic necrosis

• Focal or generalized hepatic necrosis

• Congestion, enlargement, and discoloration of liver with subcapsular hemorrhages

• Brown-yellowish color of liver in aborted fetuses

• Hemorrhagic enteritis

• Icterus (low percentage)

Differential Diagnosis

• Abortifacient agents

• Agents causing hepatitis

• Agents that cause hemorrhages

Bluetongue

• Bluetongue

• Wesselsbron disease

• Enterotoxemia of sheep

• Ephemeral fever

• Brucellosis

• Vibriosis

• Trichomonosis

Nairobi sheep disease

• Nairobi sheep disease

• Heartwater

• Ovine enzootic abortion

• Toxic plants

• Bacterial septicemias (Pasteurella, Salmonella, Anthrax)

• Rinderpest and Peste des petits ruminants

Suspect Rift Valley Fever if:

• High mortalities in lambs, kids and calves following increase in mosquito populations

• Disease is milder in adults than in newborns

• Abortions in sheep, goats and cattle

• Extensive necrotic liver changes

• Influenza symptoms in people working with sick animals or handling infected carcasses

Rift Valley Fever - Bibliography

• Linda L Logan, DVM PhD, USDA APHIS Attaché, North Africa, East Africa, Middle East, “Rift Valley Fever” CSU Foreign Animal Disease Training Course, Aug 1-5, 2005.

• Professor J A W Coetzer, Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, “Rift Valley Fever”

• USAHA, Foreign Animal Diseases, 1992 Edition, p.311-317

• W.A. Geering, A.J. Foreman and M.J. Nunn, Exotic Diseases of Animals, 1995 Australian Govt Publishing Service, Canberra; p.218- 224.

Acknowledgements

• Special thanks to

• Linda Logan, DVM PhD, USDA

• Professor JAW Coetzer

• Ken Waldrup, DVM, PhD

• Robin Sewell, DVM

• Kelsey Pohler- Research Assistant