University:
Texas A&M University
Course:
BIOL 107 | Zoology
Academic year:

2022
Views:

471

Pages:

50
Author:

Athena Harrison

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. - 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 in Africa causes abortions in sheep, cattle and goats high mortalities in lambs and kids and generalized disease in man. 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. - Host Range Mainly a disease of sheep - Host Range In Sheep Mortality in lambs under 2 weeks of age approaches 100% Mortality in older sheep reaches 30% with abortions approaching 100% - Host range Cattle are less susceptible than sheep, some are subclinical; mortality averages 5% with some abortions - Host Range Goats Buffalo - Host Range Domestic dogs and cats – susceptible but usually only have asymptomatic viremia Swine - resistant Birds - refractory, no virus isolation - Host Range Horses – have viremia but are resistant - Host range - wildlife Springbok African Buffalo Camels (in Egypt) Water buffalo in Egypt - Host range - wildlife Water buffalo - up to 50% abortion rate - Host range - wildlife Camels (in Egypt) - inapparent disease except abortions - 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 Door mice Field voles Guinea pigs Rabbits Pigs Hedgehogs Tortoises Frogs Chickens Hamster Field mice Refractive to infection Canaries Humans Pigeons Parakeets Incubation period 1-6 days 12-36 hours in lambs; will be dead before they can acquire passive immunity - Clinical signs Sheep and Goats Incubation period less than 3 days High rate of abortion at any stage of gestation Some show no symptoms - In pregnant ewes, abortion may approach 100% Aborted fetus is usually autolyzed. 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 Clinical signs Sheep and Goats Early signs o Fever 40-41°C o Loss of appetite o Jaundice o Weakness - Clinical signs Sheep and Goats Encrustation around the muzzle from bloody nasal discharge Clinical signs Sheep and Goats Some develop diarrhea - Clinical signs Sheep and Goats Acute death may occur in 20-30% of adults - Clinical signs Sheep and Goats Heavy sheep losses occur during epidemic - 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, Clinical Signs in lambs and kids Lambs seem reluctant to move; they have signs of abdominal pain, rapid respiration and listlessness. - 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. - Clinical signs in cattle Anorexia Add images Weakness Fetid diarrhea Often only sign is a drop in calving rates - 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% - Clinical signs in cattle - 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. - Clinical signs Dogs: Abortions may occur in adult dogs; severe disease and death usually only in puppies Cats: Death in kittens - Relative susceptibility Newborn ruminants Pregnant ruminants Sheep and young cattle Adult cattle, goats, sheep Humans Dogs, cats and camels Pigs - ++++ ++++ +++ ++ ++ + - Transmission RVF is primarily transmitted from animal to animal by a mosquito Aedes, Culex, Anopheles, Erehmapodites, Monsosmia - 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 - 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) - Necropsy : new-born lambs Liver massively enlarged; hemorrhages; orange-brown color; small areas of necrosis. The liver is very friable. - Necropsy : new-born lambs Gall bladder hemorrhage; Abomasum diffuse hemorrhage, serosa has petechial hemorrhage Necropsy : new-born lambs Abomasum shows diffuse chocolate brown hemorrhages, serosa has petechial hemorrhages, necrotic foci, and D. I. C. - Necropsy : adult sheep May look like plant poisoning - Necropsy : adult sheep Gall bladder contains frank hemorrhage Necropsy : sheep & cattle Abomasum is edematous similar to Heartwater Necropsy : adult cattle Close up of gall bladders - Necropsy : adult cattle Petechia - Necropsy : cattle Spleen with many hemorrhages Necropsy : other lesions Enlarged lymph nodes - Differential Diagnosis Abortifacient agents Agents causing hepatitis Agents that cause hemorrhages Differential Diagnosis Bluetongue Wesselsbron disease Enterotoxemia of sheep Ephemeral fever Brucellosis Vibriosis Trichomonosis - Differential Diagnosis 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 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 Publishing Service, Canberra; p.218- 224. -

Rift Valley Fever

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