1. Rift Valley Fever Jeffrey Musser, DVM, PhD Professor J.A.W. Coetzer
Suzanne Burnham, DVM
Texas A&M University University of Pretoria
College of Veterinary Medicine Department of
Veterinary Tropical Diseases
Rift Valley Fever- 2006

2. 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
Rift Valley Fever- 2006

3. Rift Valley Fever
In this presentation the authors especially drew from the first hand experience of their colleagues in South Africa. Personal interviews as well as standard research sources provide the insights we bring you for the recognition of this exotic disease.
JAW Coetzer
Jeffrey Musser
Suzanne Burnham
Rift Valley Fever- 2006

4. Rift Valley Fever
Rift Valley Fever (RVF) is an arthropod-borne, acute, fever-causing viral disease of sheep, goats, cattle and people.
Burnham
Rift Valley Fever- 2006

5. Rift Valley fever in Africa causes abortions in sheep, cattle and goats high mortalities in lambs and kids and generalized disease in man.
Rift Valley Fever- 2006

6. Rift Valley Fever RVF is reportable to the OIE.
It is also on the USDA and Department of Health and Human Services High Consequence lists.
Rift Valley Fever- 2006

7. 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
Logan
Rift Valley Fever- 2006

8. Rift Valley Fever
RVF was first observed when European stocks of domestic animals were introduced to Africa. These species are more severely affected than native African stock.
Rift Valley Fever- 2006

9. Rift Valley Fever Rift Valley Fever was first reported at
Lake Naivasha in Kenya.
There were many sheep
abortions and young
lambs were found
sick or dead.
Coetzer
Rift Valley Fever- 2006

10. The Rift Valley
“Africa’s Great Rift Valley is a 6,000 mile crack in the earth’s crust, stretching from Lebanon to Mozambique. One of its most dramatic sections slices through east Africa dividing Kenya into 2 segments. Geologists know that Rift Valley was formed by violent subterranean forces that tore apart the earth’s crust. These factors caused huge chunks of the crust to sink between parallel fault lines forcing up molten rock in volcanic eruptions. Kenya’s Rift Valley has a geographic feature called dambos. These are shallow depressions located often near rivers filled with water during the rainy season. A dambo can be a kilometer in length and several hundreds of meters in width. Due to the frequent presence of water, tall papyrus and several other grasses grow around their edges. These dambos are breeding grounds for mosquitoes, even in the dry season as they remain greener than other areas.”
Image and notes from Prof J A W Coetzer, Dept of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, “Rift Valley Fever” presented in Tenn at the FEAD course.

11. Rift valley fever was first reported at Lake Naivasha in Kenya
Rift valley fever was first reported at Lake Naivasha in Kenya. There were many sheep abortions and young lambs were found sick or dead.
Coetzer
Lake Naivasha

12. Major Outbreaks
Kenya and Tanzania
89,000 human cases
Cattle and sheep
2000
Saudi Arabia and Yemen
Saudi: 11,000 cases with 40 deaths reported
2002
Gambia, in 8 locations
2003, 2004
Mauritania, Senegal, Egypt, Yemen, Saudi Arabia
In Kenya
100,000 mortality in sheep
500,000 abortions
1977, 1983
In Egypt in the Nile Delta
18,000 human cases, 596 case fatality 1977
1987
Senegal River Basin/ Mauritania
The earliest reported outbreaks occurred in Kenya resulting in the death of 100,000 sheep. The 1977 Egypt outbreak affected 25.0% to 50.0% of all sheep and cattle. Among humans 200,000 fell ill, 18,000 clinical cases were confirmed with 598 deaths from haemorrhagic fevers. In 1987, RVF broke out in Mauritania following the opening of Diama Dam and resulted in more than 200 human deaths. The 1997 outbreaks in Kenya and Somalia have resulted in large losses of domestic animals, as well as, more than 300 human deaths. In September 2000, it was the first time for the disease to cross the boundaries of the African continent into Saudi Arabia and Yemen. Since then, 884 affected cases with 124 deaths in Saudi Arabia and 321 affected cases with 32 deaths in Yemen were reported.
Rift Valley Fever- 2006

13. Major Outbreaks Dates of reported outbreaks in Africa
Bres, P. (1981). Prevention of the spread of Rift Valley fever from the African continent. Contributions to Epidemiology Biostatistic, 3, from;
Bres, P. (1981). Prevention of the spread of Rift Valley fever
from the African continent. Contributions to Epidemiology Biostatistic, 3,
Rift Valley Fever- 2006

14. Kenya, Africa
Largest outbreak reported in sheep was in
100,000 mortality in sheep
500,000 abortions in sheep
Logan
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15. Kenya, Africa
Largest outbreak recorded for human cases: 89,000 cases deaths.
Flooding near
Garissa, Kenya
Logan
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16. Rift Valley Fever Outbreak 1997-98
Nomadic Refugee Camp at Garissa, 1997
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17. Rift Valley Fever Outbreak
Disease in 89,000 farm workers,
animal handlers, veterinarians
Logan
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18. Cyclic epidemics
Periodic pandemics may originate near “Dambos” or Playa lakes and spread widely
“Dambos” are depressions that accumulate water
Epidemics occur in 5-15 year cycles usually following heavy rainfall
Flooded Dambos allow the Aedes mosquitoes infected with RVF to emerge
Logan and Coetzer
Rift Valley Fever- 2006

19. A “Dambo” or Playa Lake Cattle near a “Dambo” in Kenya Logan
Rift Valley Fever- 2006

20. Playa or “Dambo” near a village
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21. Wetlands harbor mosquito populations
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22.
Rift Valley Fever- 2006

23. Enigma of Epidemiology
How is the virus maintained between epidemics?
Is there an unknown reservoir in a vertebrate population? Possibly, or
Is the virus maintained by transovarial transmission in the aedes mosquito?
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24. Transovarial Transmission in mosquitoes
Mosquito eggs dormant in soil for long period of time; survive long dry spells.
Hatch with heavy rainfall
Logan
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25. Economic Impact Livestock losses
High mortality in newborns
Abortions associated with high fever stage
Up to 50% abortions in small ruminants
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26. Economic Impact
Countries of the Arabian peninsula may ban trade of livestock from Africa
Logan
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27. Rift Valley Fever in the World in 2004, OIE
Logan
Disease reported present
Disease reported absent
Data unavailable or incomplete
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28. Rift Valley Fever Etiology Host range Incubation Clinical signs
Transmission
Diagnosis
Differential Diagnosis
Logan
Rift Valley Fever- 2006

29. Etiology RVF virus is a fairly stable virus of the Family:
Bunyaviridae
Genus:
Phlebovirus
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30. 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
Rift Valley Fever- 2006

31. Host Range
Mainly a disease of sheep
Rift Valley Fever- 2006

32. Host Range
In Sheep
Mortality in lambs under 2 weeks of age approaches 100%
Mortality in older sheep reaches 30%
with abortions
approaching 100%
Waldrup Image
Rift Valley Fever- 2006

33. Host range
Cattle are less susceptible than sheep, some are subclinical; mortality averages 5% with some abortions
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34. Host Range
Goats
Buffalo
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35. Host Range
Domestic dogs and cats – susceptible but usually only have asymptomatic viremia
Swine - resistant
Birds - refractory, no virus isolation
Logan
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36. Host Range Horses – have viremia but are resistant
Rift Valley Fever- 2006

37. Host range - wildlife Springbok African Buffalo Camels (in Egypt)
Water buffalo in Egypt
Logan
Springboks: (top Image)
(lower image)
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38. Host range - wildlife Water buffalo - up to 50% abortion rate
Image coetz
Water buffalo - up to 50% abortion rate
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39. Host range - wildlife
Camels in Egypt - Coetzer
Camels (in Egypt) - inapparent disease except abortions
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40. Rift Valley fever host range and disease severity
Mortality ~100%
Severe Illness Abortion, Low Mortality
Severe Illness Viremia Abortion
Infection Viremia
Refractive to infection
Lambs    
Calves
Kids
Puppies
Kittens
White mice
Hamster
Field mice
Door mice
Field voles
Sheep
Cattle
Goats
Water buffalo
Monkeys
Camels
Rats
Gray squirrels
Horses
Cats
Dogs
Monkeys
Guinea pigs
Rabbits
Pigs
Hedgehogs
Tortoises
Frogs
Chickens
Canaries
Pigeons
Parakeets
Humans
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41. Incubation period 1-6 days
12-36 hours in lambs; will be dead before they can acquire passive immunity
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42. Clinical signs Sheep and Goats
Incubation period less than 3 days
High rate of abortion at any stage of gestation
Some show no symptoms
Coetzer
Rift Valley Fever- 2006

43. In pregnant ewes, abortion may approach 100%
Logan
In pregnant ewes, abortion may approach 100%
Aborted fetus is usually autolyzed.
Rift Valley Fever- 2006

44. Clinical signs Sheep and Goats
Abortion rate in sheep from 40 – 100%
Ewe may also retain the placenta
Endometritis is another complication after aborting the fetus
vein.library.usyd.edu.au/.../exoimages/rd329.jpg Image contributed by US Department of Agriculture
USDA
Rift Valley Fever- 2006

45. Clinical signs Sheep and Goats
Early signs
Fever 40-41°C
Loss of appetite
Jaundice
Weakness
Rift Valley Fever- 2006

46. Clinical signs Sheep and Goats
Encrustation around the muzzle from bloody nasal discharge
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47. Clinical signs Sheep and Goats
Some develop diarrhea
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48. Clinical signs Sheep and Goats
Acute death may occur
in 20-30% of adults
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49. Clinical signs Sheep and Goats
Heavy sheep losses
occur
during epidemic
Coezter
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50. Clinical Signs in lambs and kids
Newborn Lambs, Kids: Most severe in
young lambs under 2wks old
(mortality has high as 90%)
fever (40-42°C),
anorexia,
weakness,
Coezter image
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51. Clinical Signs in lambs and kids
Lambs seem reluctant to move;
they have signs of abdominal pain,
rapid respiration and listlessness.
Coetzer
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52. Clinical Signs in lambs and kids
Death may occur within 24 to 36 hours
after the first signs appear. Death is due to severe liver necrosis and vascular collapse.
Rift Valley Fever- 2006

53. Clinical signs in cattle
Anorexia
Weakness
Fetid diarrhea
Often only sign is a drop in calving rates
Add images
logan
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54. Clinical signs in cattle
Calves: fever (40-41°C), depression. Mortality rate: 10-70% Death occurs about 2-8 days after the first signs appear.
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%
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55. Clinical signs in cattle
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56. Clinical signs in cattle
Disease most severe signs are seen in young animals
Symptoms may be prolonged and will include jaundice in some calves
Aborted calves are moderately autolyzed.
Usda?
Rift Valley Fever- 2006

57. Clinical signs
Dogs: Abortions may occur in adult dogs; severe disease and death usually only in puppies
Cats: Death in kittens
Rift Valley Fever- 2006

58. Relative susceptibility
Newborn ruminants
Pregnant ruminants
Sheep and young cattle
Adult cattle, goats, sheep
Humans
Dogs, cats and camels
Pigs
From Logan
Rift Valley Fever- 2006

59. Possible modes of spread
Infected vector insects: mosquitoes
Movement of viremic animals
Windborne movement of vectors
Contaminated viscera and tissues
Logan
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60. Transmission
RVF is primarily transmitted from animal to animal by a mosquito
Aedes, Culex, Anopheles, Erehmapodites, Monsosmia
Sheep: KAW
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61. 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 in endemic areas
Dr Linda Logan, “Rift Valley Fever” CSU Foreign Animal Disease Training Course, College of Veterinary Medicine and Biomedical Sciences, August 1-5, with permission.
Rift Valley Fever- 2006

62. Transmission
Other arthropods (Stomoxys, midges and tabanids) are able to transmit RVF by mechanical means
Coetz cow
Rift Valley Fever- 2006

63. Aerosol Transmission to Humans
RVF virus levels very high in body fluids during viremia
Virus aerosolized during butchering or necropsy of infected animals
Surgery, autopsy (humans)
Laboratory workers, Livestock handlers and butchers have the highest risk
Rift Valley Fever- 2006

64. Transmission to humans
Direct contact is also significant for humans
Humans get RVF from handling tissues, blood, secretions and excretions of infected animals.
Coetzer image
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65. Transmission to humans
Village butchers are at risk
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66. Transmission to humans
Veterinarians and Livestock handlers are at risk
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67. Transmission to humans
Milk contains virus; not known how important this is to transmission
Milk contains virus: not known how
important this is to transmission
Rift Valley Fever- 2006

68. Disease in humans Incubation 2-6 days
Many are Inapparent, or have mild flu-like symptoms
Others may have fever, headache, myalgia, nausea and painful eyes
Recovery 4-7 days
Retinopathy, loss of visual acuity
Mortality ~1%
Logan
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69. Clinical Signs in humans
RVF in humans can be a severe influenza-like disease.
Damage to retina (can lead to blindness)
High fever ( °F, °C),
Muscular pain
Nausea
Epigastric discomfort
Photophobia
Hemorrhagic fever symptoms
Encephalitis in rare instances
Rift Valley Fever- 2006

70. Retinopathy Occurs in 1-10% of affected humans Conjunctivitis
Al-Hazmi, et al. CID, 2003, 36:245. from Logan “Rift Valley Fever”
Al-Hazmi
Rift Valley Fever- 2006

71. Retinopathy Photophobia Can lead to permanent vision loss
Vasculitis, retinitis, detachment of retina, hemorrhage, 15% affected humans develop ocular complications - Coetzer
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72. Diagnosis in Animals Tentative diagnosis- Field Diagnosis:
epidemiological, clinical and pathological features
Confirmation of diagnosis:
1. Virus isolation
liver, spleen and blood
2. Antigen capture ELISA
3. PCR
4. Serology
CF test
Virus neutralization
ELISA
other
5. Histopathology : Immunohistochemistry
Coetzer
Rift Valley Fever- 2006

73. Diagnosis Sample collection: Heparinized blood Spleen Liver
Acute and convalescent serum samples
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74. Diagnosis Virus isolation in cell culture Virus neutralization
Antigen detection by IF staining
ELISA
Polymerase Chain Reaction (PCR)
Logan
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75. Clinical Pathology Leucopenia Increased liver enzymes
Prolonged clotting time, thrombocytopenia
Disseminated intravascular coagulopathy
Logan
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76. 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
Rift Valley Fever- 2006

77. Pathology Summary
Widespread cutaneous hemorrhages, petechial to ecchymotic hemorrhages on parietal and visceral serosal membranes
Enlargement, edema, hemorrhages and necrosis of lymph nodes
Congestion and cortical hemorrhages of kidneys and gallbladder
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)
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78. Necropsy : new-born lambs
Liver massively enlarged; hemorrhages; orange-brown color; small areas of necrosis.
Gall bladder hemorrhage; Abomasum diffuse chocolate brown hemorrhage, serosa has petechial hemorrhage - Coetzer
Liver massively enlarged; hemorrhages; orange-brown color;
small areas of necrosis. The liver is very friable.
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79. Necropsy : new-born lambs
Gall bladder hemorrhage; Abomasum diffuse hemorrhage,
serosa has petechial hemorrhage
Liver massively enlarged; hemorrhages; orange-brown color; small areas of necrosis.
Gall bladder hemorrhage; Abomasum diffuse chocolate brown hemorrhage, serosa has petechial hemorrhage - Coetzer
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80. Necropsy : new-born lambs
Abomasum shows diffuse chocolate brown hemorrhages,
serosa has petechial hemorrhages, necrotic foci, and D. I. C.
Abomasum diffuse chocolate brown hemorrhage, serosa has petechial hemorrhage;
Necrotic Foci, D. I. C. – Coetzer
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81. Necropsy : adult sheep May look like plant poisoning
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82. Necropsy : adult sheep Gall bladder contains frank hemorrhage
Coetzer images
Gall bladder contains frank hemorrhage
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83. Necropsy : sheep & cattle
Coetzer images
Abomasum is edematous similar to Heartwater
Abomasum is edematous similar to Heartwater
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84. Necropsy : adult cattle
Close up of gall bladders- Coetzer images
Close up of gall bladders
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85. Necropsy : adult cattle
Petechiation
Coetzer images
Petecciation
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86. Necropsy : cattle Spleen with many hemorrhages
Spleen with many hemorrhages - Coetzer
Spleen with many hemorrhages
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87. Necropsy : other lesions
Enlarged
lymph nodes
Enlarged lymph nodes
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88. Differential Diagnosis
Abortifacient agents
Agents causing hepatitis
Agents that cause hemorrhages
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89. Differential Diagnosis
Bluetongue
Wesselsbron disease
Enterotoxemia of sheep
Ephemeral fever
Brucellosis
Vibriosis
Trichomonosis
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90. Differential Diagnosis
Nairobi sheep disease
Heartwater
Ovine enzootic abortion
Toxic plants
Bacterial septicemias (Pasteurella, Salmonella, Anthrax)
Rinderpest and Peste des petits ruminants
Rift Valley Fever- 2006

91. 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
Logan
Rift Valley Fever- 2006

92. 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
W.A. Geering, A.J. Foreman and M.J. Nunn, Exotic Diseases of Animals, 1995 Australian Govt Publishing Service, Canberra; p
Rift Valley Fever- 2006

93. An excellent video about Rift Valley Fever is available from:
Rift Valley Fever- 2006

94. Image Watermark “KAW” images by Dr. Ken A. Waldrup
“Coetzer” images used with permission by Dr. J.A.W. Coetzer
“LLogan” images by Dr. Linda Logan
“Suz” images by Dr Suzanne Burnham
“MFitilodze” images by Dr. M. W. (Bill) Mfitilodze Bunda College of Agriculture, University of Malawi
Rift Valley Fever- 2006

95. This presentation is a collaborative effort

96. Acknowledgements Special thanks to
Professor JAW Coetzer Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, U of Pretoria
Linda Logan, DVM PhD, USDA International Services, Attaché
Ken Waldrup, DVM, PhD, Texas Department of State Health Services
Robin Sewell, DVM, Texas A&M University College of Veterinary Medicine, Librarian
Kelsey Pohler- Research Assistant, TAMU
Linda Venter, Instructional Designer, Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, U of Pretoria
Lilly Mphahlele, Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, U of Pretoria
Rift Valley Fever- 2006