1. ARBAMINCH UNIVERSITY
SCOOL OF POST GRADUATE STUDY
Arthropod - Borne Animal Diseases and Zoonosis (PVEDC
616)
Medical Entomology and Vector control
By:
Abate Waldetensai
May, 2018
3. Presentation layout
RiftValley Disease definition
Agent/ Aetology
Distribution
Host range
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Host range
Epidemiology
Transmission
Necropsy Finding
Clinical Presentation
4. Presentation layout
Diagnosis of RVF
Morbidity and Mortality
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Treatment, prevention and control
Conclusion
5. Definition
RiftValley fever (RVF) is zoonotic
mosquito- borne Acute febrile viral
disease affecting animals & humans
Characterized by high morbidity,
mortality & economic loss
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6. The disease is endemic in sub-Saharan Africa
The most common form of the disease is a self-
limiting, flu-like illness; however, ocular disease and
rare cases of fatal hemorrhagic fever also occur.
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7. Agents/etiology
Rift Valley fever (RVF) virus is a negative-sense, single-stranded
RNA virus of the family Bunyaviridae within the genus
Phlebovirus.
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Phlebovirus.
The largest family including more than 350 members with
large diversity
Only one serotype is recognized but strains exist of variable
virulence
9. Distribution and History of RVF
The virus has grown significantly in most countries of the
African continent and Madagascar.
It emerged for the first time outside Africa in the Arabian
Peninsula in 2000–2001.
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Peninsula in 2000–2001.
More recently, it was detected for the first time in the
Archipelago of Comores, located between Mozambique and
Madagascar.
10. Cont….
RVF virus was first identified in 1931 during an investigation
into an epidemic among sheep on a farm in the Rift Valley of
Kenya
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In 1977 an explosive outbreak was reported in Egypt that
introduced via infected livestock trade along the Nile
irrigation system.
11. Cont…
In 1997–98, a major outbreak occurred in Kenya, Somalia and
Tanzania following El Niño event and extensive flooding.
Following infected livestock trade from the horn of Africa,
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Following infected livestock trade from the horn of Africa,
RVF spread in September 2000 to Saudi Arabia andYemen
12. The virus can infects many species of animals and humans
o Cattle, sheep, goats, dromedaries, several rodents
o Wild ruminants, buffaloes, antelopes, wildebeest, etc.
Host range
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o Humans are very susceptible (major zoonosis)
o African monkeys and domestic carnivores present a transitory
viraemia
13. Cont…
o The primary amplifying hosts are sheep and cattle.
o In endemic regions, epidemics of Rift Valley fever can be
recognized by high mortality rates in young animals and
abortions in adults.
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abortions in adults.
o Sheep seemed to be the most susceptible animal
o RVF can cause high rates of abortions during pregnancy and high
mortalities among newborns
14. Cont…
o Lambs can die before they acquire passive immunity and
mortality
o Abortion rates among old sheep range from 5 to 100%
o Infections can therefore cause severe disease and result in
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o Infections can therefore cause severe disease and result in
significant economic losses
15. Rift Valley fever host range and disease severity
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16. Epidemiology
o RVF disease usually presents in an epizootic form over large
areas of a country
o Heavy rains and sustained flooding are cause for the disease
occurrence
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occurrence
17. Cause of Outbreak
Rainfall
Wetlands and stagnantWater
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Flourishing of Mosquito
Transmission of infection
19. Outbreaks Occurrences
Date Country
1950-19 Kenya
1967-1970 Nigeria
1969 Central African Republic
1976-1977 Sudan
1977-1980 Egypt
1987 Mauritania
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1987 Mauritania
1990-1991 Madagascar
1993 Egypt – Senegal
1997 Kenya – Somalia
1999 South Africa
2000-2001 Saudi Arabia - Yemen
20. Transmission of RVF
Vectors (Mosquitoes)
Infected Aedes feed preferentially on domestic
ruminants which act as an amplifier of RVF
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Broad vector range of mosquitoes (Aedes, Anopheles,
Culex, Mansonia, etc.)
Extrinsic incubation also occurs in vectors
Other blood suckling insects such as ticks and midges
21. Transmission (Cont…)
Mechanical transmission by various vectors has been
demonstrated in laboratory studies
Sylvatic cycle and inter-epidemic maintenance also occurs in some
areas
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areas
Direct contamination: occurs in humans when handling infected
animals and meat or Contact with blood or other body fluids of
infected animals
Consumption of infected milk
22. Transmission (cont..)
Airborne transmission
Inoculation through broken skin
Both animals and humans theoretically have the potential to
introduce Rift Valley fever into new areas by infecting
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introduce Rift Valley fever into new areas by infecting
mosquitoes
23. Transmission cycles of RVF
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24. Transmission cycles of RVF (cont…)
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25. Necropsy findings
Massive hepatitis: hemorrhages, necrotic foci, marked
enlargement, orange-brown, friable, edematous liver tissue
Chocolate-brown digested blood in abomasums,
hemorrhages in intestinal mucosa, free blood in lumen
Example: in new born Lambs, Gall bladder hemorrhage;
Abomasums diffuse hemorrhage, serosa has petechial hemorrhage
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26. Necropsy
Postmortem , or postmortem examination
Dissection and examination of a dead body and its
organs and structures to determine the cause of death,
Observe the effects of disease,
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Observe the effects of disease,
Establish the sequences of changes and thus establish
evolution and mechanisms of disease processes.
27. Summery of Necropsy
Focal or generalized
hepatic necrosis
Congestion, enlargement,
and discoloration of liver
with sub capsular
hemorrhages
Widespread cutaneous hemorrhages,
petechial to ecchymotic hemorrhages
on parietal and visceral serosal
membranes
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hemorrhages
Brown-yellowish color of
liver in aborted fetuses
Hemorrhagic enteritis
Icterus (low percentage)
membranes
Enlargement, edema, hemorrhages
and necrosis of lymph nodes
Congestion and cortical hemorrhages
of kidneys and gallbladder
28. Source ofVirus/infection
Fauna
Vectors
secretions after abortion in animals,
Animals Human
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secretions after abortion in animals,
mosquitoes,
and infected meat;
aerosols and possibly consumption of raw
milk
31. Sheep and Goats
Early signs
o Fever 40-41°C
o Loss of appetite
o Jaundice
oWeakness
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Acute death may
occur
in 20-30% of adults
Encrustation around the
muzzle from bloody nasal
discharge
oWeakness
32. Abortion
Incubation period less than 3 days
Some show no symptoms
Abortion rate in sheep from 40 – 100%
Ewe may also retain the placenta
Endometritis is another complication after aborting the fetus
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36. Morbidity and Mortality
The mortality rate can be very high in young animals
The mortality rates in adult sheep can vary from 5% to
almost 100% in different epidemics and on different
farms.
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farms.
The estimated mortality rate in calves varies from 10%
to 70%, but fewer than 10% of infections in adult cattle
are usually fatal.
37. Cont…
Up to 85% of cattle abortion in some outbreaks,
Abortion rates in camels can be as high as in cattle
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38. Treatment, Prevention and Control
Treatment
o No specific treatment, other than supportive care is
available.
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39. Prevention and Control
1 - Animal
Vaccination of unaffected animals
Live attenuated vaccine
Killed or Inactive vaccine
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Killed or Inactive vaccine
Notification of affected animals
Application of safe insecticides to eradicate blood
suckling insects
40. Prevention and control (cont…)
1 - Animal
Periodic surveillance of susceptible animals to assess
immune status
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immune status
Application of quarantine measures for testing of
imported animals
Rapid burial of dead bodies
41. Prevention and control (cont..)
2 –Vector
Removal of stagnant water
Weekly treatment of water collections using insecticides
Application of insecticides every other day in all gardens
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Application of insecticides every other day in all gardens
Removal of objects that can act as possible water
containers
42. Prevention and control (cont…)
3 – Human ( General Measures)
Sleeping indoors
Using bed nets during sleep
Putting screens on windows
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Putting screens on windows
Wearing clothes that protects whole body
Applying mosquito repellents
Using spray on clothes and Houses
43. Conclusion
RVF is spreading outside Africa
Although often mild, may lead to high morbidity and
mortality
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No vaccine for humans
No specific treatment
Preventive measures are crucial