RiftValleyFever - Rift Valley Fever Jeffrey Musser DVM PhD...

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Unformatted text preview: Rift Valley Fever Jeffrey Musser, DVM, PhD Suzanne Burnham, DVM Texas A&M University College of Veterinary Medicine Professor J.A.W. Coetzer University of Pretoria Department of Veterinary Tropical Diseases Rift Valley Fever- 2006 Rift Fever- 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 Professor Diseases, Faculty of Veterinary Science, University of Pretoria, “Rift Valley Fever” presented at the FEAD course in Knoxville, Tenn. 2005. Rift Valley Fever- 2006 Rift Fever- 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 Rift Fever- Rift Valley Fever Rift Valley Fever (RVF) is an arthropod-borne, acute, fever-causing viral disease of sheep, goats, cattle and people. Rift Valley Fever- 2006 Rift Fever- 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 Rift Fever- Rift Valley Fever RVF is reportable to the OIE. It is also on the USDA and It Department of Health and Human Services High Consequence lists. High Rift Valley Fever- 2006 Rift Fever- 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 Rift Valley Fever- 2006 Rift Fever- 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 Rift Fever- 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. Rift Valley Fever- 2006 Rift Fever- The Rift Valley The Lake Naivasha Lake Major Outbreaks 1997-1998 1950-1951 – 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 – 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 Rift Valley Fever- 2006 Rift Fever- Major Outbreaks Major 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, 178-190. Rift Valley Fever- 2006 Rift Fever- Kenya, Africa 1950-1951 Largest outbreak reported in sheep was in 1950-1951 100,000 mortality in sheep 500,000 abortions in sheep Rift Valley Fever- 2006 Rift Fever- Kenya, Africa 1997-1998 Largest outbreak recorded for human cases: 89,000 cases - 478 deaths. Flooding near Garissa, Kenya Rift Valley Fever- 2006 Rift Fever- Rift Valley Fever Outbreak 1997-98 Nomadic Refugee Camp at Garissa, 1997 Rift Valley Fever- 2006 Rift Fever- Rift Valley Fever Outbreak Disease in 89,000 farm workers, animal handlers, veterinarians Rift Valley Fever- 2006 Rift Fever- 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 Epidemics usually following heavy rainfall Flooded Dambos allow the Aedes Aedes mosquitoes infected with RVF to emerge Rift Valley Fever- 2006 Rift Fever- A “Dambo” or Playa Lake Cattle near a “Dambo” in Kenya Rift Valley Fever- 2006 Rift Fever- Playa or “Dambo” near a village Rift Valley Fever- 2006 Rift Fever- Wetlands harbor mosquito populations Rift Valley Fever- 2006 Rift Fever- http://www.elib.hbi.ir/persian/EMERGING_EBOOK/20_RIFT_VALLEY_FEVER_files/image005.jpg Rift Valley Fever- 2006 Rift Fever- 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? Rift Valley Fever- 2006 Rift Fever- Transovarial Transmission in mosquitoes Mosquito eggs dormant in soil for long period of time; survive long dry spells. Hatch with heavy rainfall Rift Valley Fever- 2006 Rift Fever- Economic Impact Livestock losses High mortality in newborns Abortions associated with high fever stage Up to 50% abortions in small ruminants Rift Valley Fever- 2006 Rift Fever- Economic Impact Countries of the Arabian peninsula may ban trade of livestock from Africa Rift Valley Fever- 2006 Rift Fever- Rift Valley Fever in the World in 2004, OIE http://www.oie.int/eng/info/en_presdistribgeo.htm Disease reported present Disease reported absent Data unavailable or incomplete Rift Valley Fever- 2006 Rift Fever- Rift Valley Fever Etiology Host range Incubation Clinical signs Clinical Transmission Diagnosis Differential Diagnosis Differential Rift Valley Fever- 2006 Rift Fever- Etiology RVF virus is a fairly stable virus of the Family: Bunyaviridae Genus: Phlebovirus Rift Valley Fever- 2006 Rift Fever- Etiology RVF virus is serologically related to other phleboviruses, but can be differentiated by serum neutralization tests. Enveloped RNA virus Enveloped There is only one serotype of RVF virus However, there is different pathogenicity among strains of RVF virus Rift Valley Fever- 2006 Rift Fever- Host Range Mainly a disease of sheep Rift Valley Fever- 2006 Rift Fever- Host Range In Sheep Mortality in lambs under 2 weeks of age approaches 100% Mortality in older sheep reaches 30% with abortions approaching 100% Rift Valley Fever- 2006 Rift Fever- Host range Cattle are less susceptible than sheep, some are subclinical; mortality averages 5% with some abortions Rift Valley Fever- 2006 Rift Fever- Host Range Goats Buffalo Rift Valley Fever- 2006 Rift Fever- Host Range Domestic dogs and cats – susceptible but usually only have asymptomatic viremia Swine - resistant Birds - refractory, no virus isolation Rift Valley Fever- 2006 Rift Fever- Host Range Horses – have viremia but are resistant Rift Valley Fever- 2006 Rift Fever- Host range - wildlife Springbok African Buffalo Camels (in Egypt) Camels Water buffalo in Egypt Water Rift Valley Fever- 2006 Rift Fever- Host range - wildlife Water buffalo - up to 50% abortion rate Rift Valley Fever- 2006 Rift Fever- Host range - wildlife Camels (in Egypt) - inapparent disease except abortions Rift Valley Fever- 2006 Rift Fever- Rift Valley fever host range and disease severity Mortality ~100% Severe Illness Abortion, Low Mortality Severe Illness Viremia Abortion Infection Viremia Lambs Sheep Monkeys Horses Cattle Camels Cats Goats Rats Dogs Gray squirrels Monkeys Calves Kids Puppies Kittens Water buffalo White mice Guinea pigs Rabbits Pigs Hedgehogs Tortoises Frogs Chickens Hamster Field mice Refractive to infection Canaries Pigeons Humans Door mice Parakeets Field voles Rift Valley Fever- 2006 Rift Fever- Incubation period 1-6 days 12-36 hours in lambs; will be dead before they can acquire passive immunity Rift Valley Fever- 2006 Rift Fever- Clinical signs Sheep and Goats Incubation period less than 3 days High rate of abortion at any stage of gestation Some show no symptoms Rift Valley Fever- 2006 Rift Fever- In pregnant ewes, abortion may approach 100% Aborted fetus is usually autolyzed. Rift Valley Fever- 2006 Rift Fever- 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 USDA Rift Valley Fever- 2006 Rift Fever- Clinical signs Sheep and Goats Early signs Fever 40-41°C Loss of appetite Jaundice Jaundice Weakness Rift Valley Fever- 2006 Rift Fever- Clinical signs Sheep and Goats Encrustation around the muzzle from bloody nasal discharge Rift Valley Fever- 2006 Rift Fever- Clinical signs Sheep and Goats Some develop diarrhea Rift Valley Fever- 2006 Rift Fever- Clinical signs Sheep and Goats Acute death may occur in 20-30% of adults Rift Valley Fever- 2006 Rift Fever- Clinical signs Sheep and Goats Heavy sheep losses occur during epidemic Rift Valley Fever- 2006 Rift Fever- 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, Rift Valley Fever- 2006 Rift Fever- Clinical Signs in lambs and kids Lambs seem reluctant to move; they have signs of abdominal pain, rapid respiration and listlessness. Rift Valley Fever- 2006 Rift Fever- 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 Rift Fever- Clinical signs in cattle Anorexia Add images Weakness Fetid diarrhea Often only sign is a drop in calving rates Rift Valley Fever- 2006 Rift Fever- 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, Adults: anorexia, weakness, fetid diarrhea, fall in milk yield. Abortion may reach 85% in the herd. Mortality rate is usually less than 10% Rift Valley Fever- 2006 Rift Fever- Clinical signs in cattle Rift Valley Fever- 2006 Rift Fever- 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. Rift Valley Fever- 2006 Rift Fever- 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 Rift Fever- Relative susceptibility Newborn ruminants Pregnant ruminants Sheep and young cattle Adult cattle, goats, sheep Humans Dogs, cats and camels Pigs Rift Valley Fever- 2006 Rift Fever- ++++ ++++ ++++ ++++ +++ +++ ++ ++ + - Possible modes of spread Infected vector insects: mosquitoes Movement of viremic animals Windborne movement of vectors Contaminated viscera and tissues Rift Valley Fever- 2006 Rift Fever- Transmission RVF is primarily transmitted from animal to animal by a mosquito Aedes, Culex, Anopheles, Aedes Erehmapodites, Monsosmia Rift Valley Fever- 2006 Rift Fever- 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 Rift Valley Fever- 2006 Rift Fever- Transmission Other arthropods (Stomoxys, midges and tabanids) are able to transmit RVF by mechanical means Rift Valley Fever- 2006 Rift Fever- 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 Rift Fever- Transmission to humans Direct contact is also significant for humans Humans get RVF from handling tissues, blood, secretions and excretions of infected animals. Rift Valley Fever- 2006 Rift Fever- Transmission to humans Village butchers are at risk Rift Valley Fever- 2006 Rift Fever- Transmission to humans Veterinarians and Livestock handlers are at risk Rift Valley Fever- 2006 Rift Fever- Transmission to humans Milk contains virus: not known how important this is to transmission Rift Valley Fever- 2006 Rift Fever- 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% Mortality Rift Valley Fever- 2006 Rift Fever- 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 Muscular Nausea Epigastric discomfort Photophobia Hemorrhagic fever symptoms Encephalitis in rare instances Rift Valley Fever- 2006 Rift Fever- Retinopathy Occurs in 1-10% of affected humans Conjunctivitis Al-Hazmi Rift Valley Fever- 2006 Rift Fever- Retinopathy Photophobia Can lead to permanent vision loss Rift Valley Fever- 2006 Rift Fever- Diagnosis in Animals Tentative diagnosis- Field Diagnosis: 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 •CF •Virus neutralization •Virus •ELISA •ELISA •other •other 5. Histopathology : Immunohistochemistry Rift Valley Fever- 2006 Rift Fever- Diagnosis Sample collection: Heparinized blood Spleen Liver Acute and convalescent serum samples Rift Valley Fever- 2006 Rift Fever- Diagnosis Virus isolation in cell culture Virus neutralization Antigen detection by IF staining ELISA Polymerase Chain Reaction (PCR) Rift Valley Fever- 2006 Rift Fever- Clinical Pathology Leucopenia Increased liver enzymes Prolonged clotting time, thrombocytopenia Disseminated intravascular coagulopathy Rift Valley Fever- 2006 Rift Fever- 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 Rift Fever- Pathology Summary Focal or generalized hepatic necrosis Congestion, enlargement, Congestion, and discoloration of liver with subcapsular hemorrhages Brown-yellowish color of Brown liver in aborted fetuses Hemorrhagic enteritis Hemorrhagic Icterus (low percentage) Icterus Widespread cutaneous Widespread hemorrhages, petechial to ecchymotic hemorrhages on parietal and visceral serosal membranes Enlargement, edema, Enlargement, hemorrhages and necrosis of lymph nodes Congestion and cortical Congestion hemorrhages of kidneys and gallbladder Rift Valley Fever- 2006 Rift Fever- Necropsy : new-born lambs Liver massively enlarged; hemorrhages; orange-brown color; small areas of necrosis. The liver is very friable. Rift Valley Fever- 2006 Rift Fever- Necropsy : new-born lambs Gall bladder hemorrhage; Abomasum diffuse hemorrhage, serosa has petechial hemorrhage Rift Valley Fever- 2006 Rift Fever- Necropsy : new-born lambs Abomasum shows diffuse chocolate brown hemorrhages, serosa has petechial hemorrhages, necrotic foci, and D. I. C. Rift Valley Fever- 2006 Rift Fever- Necropsy : adult sheep May look like plant poisoning Rift Valley Fever- 2006 Rift Fever- Necropsy : adult sheep Gall bladder contains frank hemorrhage Rift Valley Fever- 2006 Rift Fever- Necropsy : sheep & cattle Abomasum is edematous similar to Heartwater Rift Valley Fever- 2006 Rift Fever- Necropsy : adult cattle Close up of gall bladders Rift Valley Fever- 2006 Rift Fever- Necropsy : adult cattle Petecciation Rift Valley Fever- 2006 Rift Fever- Necropsy : cattle Spleen with many hemorrhages Rift Valley Fever- 2006 Rift Fever- Necropsy : other lesions Enlarged lymph nodes Rift Valley Fever- 2006 Rift Fever- Differential Diagnosis Abortifacient agents Agents causing hepatitis Agents that cause hemorrhages Rift Valley Fever- 2006 Rift Fever- Differential Diagnosis Bluetongue Wesselsbron disease Wesselsbron Enterotoxemia of sheep Enterotoxemia Ephemeral fever Ephemeral Brucellosis Brucellosis Vibriosis Vibriosis Trichomonosis Rift Valley Fever- 2006 Rift Fever- Differential Diagnosis Nairobi sheep disease Heartwater Heartwater Ovine enzootic abortion Ovine Toxic plants Toxic Bacterial septicemias (Pasteurella, Bacterial Salmonella, Anthrax) Rinderpest and Peste des petits ruminants Rift Valley Fever- 2006 Rift Fever- 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- 2006 Rift Fever- Rift Valley Fever Bibliography 1. 2. 3. 4. 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 Diseases Publishing Service, Canberra; p.218- 224. Rift Valley Fever- 2006 Rift Fever- An excellent video about Rift Valley Fever is available from: http://www.up.ac.za/academic/veterinary/depts_vtd_teach/index.htm Rift Valley Fever- 2006 Rift Fever- 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 Rift Fever- This presentation is a collaborative effort 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 Rift Fever- ...
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