Rift valley fever ppt.

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

22-May-18Arthropod - Borne Animal Diseases and Zoonosis (PVEDC 616)2

Presentation layout
RiftValley Disease definition
Agent/ Aetology
Distribution
Host range
Host range
Epidemiology
Transmission
Necropsy Finding
Clinical Presentation

Presentation layout
 Diagnosis of RVF
 Morbidity and Mortality
22-May-18
Arthropod - Borne Animal Diseases and Zoonosis (PVEDC 616)
2
 Treatment, prevention and control
 Conclusion

Definition
RiftValley fever (RVF) is zoonotic
mosquito- borne Acute febrile viral
disease affecting animals & humans
Characterized by high morbidity,
mortality & economic loss

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.
22-May-18Arthropod - Borne Animal Diseases and
Zoonosis (PVEDC 616)
3

Agents/etiology
 Rift Valley fever (RVF) virus is a negative-sense, single-stranded
RNA virus of the family Bunyaviridae within the genus
Phlebovirus.
Phlebovirus.
 The largest family including more than 350 members with
large diversity
 Only one serotype is recognized but strains exist of variable
virulence

Aetology (cont..)
Family

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.
Peninsula in 2000–2001.
 More recently, it was detected for the first time in the
Archipelago of Comores, located between Mozambique and
Madagascar.

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
 In 1977 an explosive outbreak was reported in Egypt that
introduced via infected livestock trade along the Nile
irrigation system.

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,
Following infected livestock trade from the horn of Africa,
RVF spread in September 2000 to Saudi Arabia andYemen

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
o Humans are very susceptible (major zoonosis)
o African monkeys and domestic carnivores present a transitory
viraemia

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.
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

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
o Infections can therefore cause severe disease and result in
significant economic losses

Rift Valley fever host range and disease severity

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
occurrence

Cause of Outbreak
Rainfall
Wetlands and stagnantWater
Flourishing of Mosquito
Transmission of infection

Outbreaks Occurrences
Date Country
1950-19 Kenya
1967-1970 Nigeria
1969 Central African Republic
1976-1977 Sudan
1977-1980 Egypt
1987 Mauritania
1987 Mauritania
1990-1991 Madagascar
1993 Egypt – Senegal
1997 Kenya – Somalia
1999 South Africa
2000-2001 Saudi Arabia - Yemen

Transmission of RVF
Vectors (Mosquitoes)
 Infected Aedes feed preferentially on domestic
ruminants which act as an amplifier of RVF
 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

Transmission (Cont…)
 Mechanical transmission by various vectors has been
demonstrated in laboratory studies
 Sylvatic cycle and inter-epidemic maintenance also occurs in some
areas
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

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
introduce Rift Valley fever into new areas by infecting
mosquitoes

Transmission cycles of RVF
20

Transmission cycles of RVF (cont…)

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
22

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,
23
 Observe the effects of disease,
 Establish the sequences of changes and thus establish
evolution and mechanisms of disease processes.

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
24
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

Source ofVirus/infection
 Fauna
Vectors
secretions after abortion in animals,
Animals Human
secretions after abortion in animals,
 mosquitoes,
and infected meat;
aerosols and possibly consumption of raw
milk

Clinical Presentation
Cattle

Lambs and kids

Sheep and Goats
Early signs
o Fever 40-41°C
o Loss of appetite
o Jaundice
oWeakness
28
Acute death may
occur
in 20-30% of adults
 Encrustation around the
muzzle from bloody nasal
discharge
oWeakness

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

Relative susceptibility
30

Diagnosis of RVF
 Antibody detection
 ELISA
 EIA
 Virus detection
 Virus detection
 Virus isolation
 Antigen detection
 PCR

Differential Diagnosis
 Bluetongue
 Wesselsbron disease
 Brucellosis
 Vibriosis
 Vibriosis

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.
farms.
 The estimated mortality rate in calves varies from 10%
to 70%, but fewer than 10% of infections in adult cattle
are usually fatal.

Cont…
 Up to 85% of cattle abortion in some outbreaks,
 Abortion rates in camels can be as high as in cattle

Treatment, Prevention and Control
Treatment
o No specific treatment, other than supportive care is
available.

Prevention and Control
1 - Animal
 Vaccination of unaffected animals
 Live attenuated vaccine
Killed or Inactive vaccine
 Killed or Inactive vaccine
 Notification of affected animals
 Application of safe insecticides to eradicate blood
suckling insects

Prevention and control (cont…)
1 - Animal
 Periodic surveillance of susceptible animals to assess
immune status
immune status
 Application of quarantine measures for testing of
imported animals
 Rapid burial of dead bodies

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
 Application of insecticides every other day in all gardens
 Removal of objects that can act as possible water
containers

Prevention and control (cont…)
3 – Human ( General Measures)
 Sleeping indoors
 Using bed nets during sleep
Putting screens on windows
22-May-18Arthropod - Borne Animal Diseases and Zoonosis (PVEDC 616)
39
 Putting screens on windows
 Wearing clothes that protects whole body
 Applying mosquito repellents
 Using spray on clothes and Houses

Conclusion
 RVF is spreading outside Africa
 Although often mild, may lead to high morbidity and
mortality
 No vaccine for humans
 No specific treatment
 Preventive measures are crucial

ThankYou!!!
What is out of sight is all too often out of mind
22-May-18

Rift valley fever ppt.

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