Rift Valley Fever (RVF)

By /

Rift Valley Fever (RVF)

Rift Valley Fever (RVF) also known as Enzootic Hepatitis in animals.

Rift Valley Fever (RVF) is a vector-borne disease of sheep, cattle and goat is characterized by high rate of abortion and neonatal mortality particularly in sheep, goat and cattle considerably.

Etiology

  • Rift Valley Fever (RVF) is caused by Rift valley fever virus, genus Phlebovirus of the family Bunyaviridae a negative-sense, single-stranded RNA virus, contain one serotype.
  • The virus is inactivated at pH < 6.8, highly susceptible to low concentration of formalin and strong solution of sodium or calcium hypochlorite.

Epidemiology

  • Rift valley fever was initially reported in rift valley in Kenya; now exist in sub-Saharan Africa, Egypt and Madagascar.
  • Rift valley fever like disease is reported in sheep in India. The disease is usually epidemic following heavy rains and flooding.
  • Mortality rate in New born lambs: 70-100%, Adult sheep: 10-30% and Cattle: 10%

Host affected

  • Sheep, cattle, goats, wild ruminants like antelope and wilde beest.
  • Humans are very susceptible (major zoonosis).

Pathogenesis

Pathogenesis of Rift Valley Fever (RVF)
Pathogenesis of Rift Valley Fever (RVF)

Clinical manifestation

Neonates

  • Incubation period: 12-36 hrs in lambs.
  • Sudden onset of high fever (biphasic fever temp 41oC).
  • Reluctant to move  or feed, abdominal pain.
  • Inco-ordination followed by collapse and death.

Adult sheep and cattle

  • Abortion- 85 % in cattle, and 100% in sheep.
  • Sudden death preceded by high fever, sick animal may regurgitate and develop bad smelling  bloody diarrhoea and icterus, which is common in cattle.
  • Serosanguineous or blood stained mucopurulent nasal discharge.
  •  Increased respiratory rate may also be seen.

Necropsy Findings

  • Focal or generalised hepatic necrosis (white necrotic foci of about 1 mm in diameter).
  • Brown-yellowish colour of liver in aborted foetuses.

Sample collection

  • Whole blood, paired sera sample and aborted foetus from live animals.
  • Liver, spleen, kidney, lymph node, heart blood  and brain from dead animals.

Diagnosis

  • Based on clinical signs and lesions.
  • Severe leukopenia.
  • Agar gel immunodiffusion test.
  • Viral antigen could be detected by RT-PCR.
  • Antibodies in serum by  AGID,VNT and ELISA.

Differential diagnosis

Prevention and control

  • Control of vector.
  • Movement of stock to high lying area.
  • Vaccination of  lambs with live attenuated vaccine at 6 months of age.
  • Vaccination is normally not to be used for pregnant animals, because it may cause abortion, congenital defect or hydrops amnii in the ewe.

Related Posts

Scroll to Top