80. Rift Valley fever and Nairobi sheep disease.

Question 1

Rift valley fever info and resistance?

Answer 1

Rift Valley Fever

• Notifiable disease
• Causative agent: Rift Valley fever virus (RVFV, Phenuiviridae, Phlebovirus)

Resistance

• • 60 - 23℃, 50-85% relative humidity
• Detergent, lipid solvent, low pH inactivates

Question 2

Epidemiology of rift valley?

Answer 2

Epidemiology

• Endemic in tropical Africa: epizootic in 5-20 year cycles, after abnormally heavy rainfall, outbreak peaks in late summer
• Outside of Africa: Saudi Arabia, Yemen
• Vectors
• Primary vectors: Aedes mosquitoes ➝ germinative transmission, eggs survive for years, large-scale hatching after heavy rainfall
• Secondary vectors: Culex, Anopheles mosquitoes, sandflies, black flies, midges, flies

• Vertebrate hosts: ruminants, humans (enough high viraemia for vector infection)

Question 3

Transmission of Rift valley?

Answer 3

Transmission

• Vectorial: several vectors, European species competent
• Non-vectorial
• Direct contact or air-borne
• Tissues and body fluids of infected animals
• Aborted foetuses, slaughter, dissection

• Direct human to human transmission rare

Question 4

Susceptibility of Rift valley?

Answer 4

Susceptibility

• 100% mortality: young ruminants, puppies, kittens
• Severe disease, abortion, death ➝ sheep, cattle, goat, human
• Severe disease, abortion ➝ monkey, camel, rat, squirrel
• Infection, viraemia ➝ horse, dog, cat, monkey
• Resistant ➝ rabbit, swine, rodents, birds

Question 5

Pathogenesis of Rift valley?

Answer 5

Pathogenesis

1. Infection ➝ 24-48 h incubation ➝ viraemia 4-5 days ➝ spread in body
2. Virus replication in endothel cells of blood vessels, respiratory tract/GI mucosa epithel cells, hepatocytes ➝ haemorrhages,

bloody diarrhoea, icterus

3. Gets to CNS ➝ bloody-serous lymphocytic meningitis, encephalitis
4. Gets to foetus ➝ replicates in every organ (liver) ➝ increased abortion cases

Question 6

Clinical signs of Rift valley?

Answer 6

Clinical signs

• Sheep, Goat

• Incubation: < 3 days
• 5-100% abortion, at any stage of pregnancy
• Sudden death
• Diarrhoea, icterus, mucopurulent nasal discharge, subclinical infections
• Lambs, kids ➝ Incubation: 12-36 h, high fever, depression, anorexia, death within 12-48 h, under 1 week: > 90% lethality, over

2 weeks: 20% lethality

• Cattle

• Fever, weakness, anorexia, salivation, diarrhoea, icterus
• Abortion: 100%, Lethality: 10%
• Calves ➝ signs similar to those in lambs, 10-70% lethality

• Human

• Incubation: 2-6 days
• Subclinical or influenza-like disease ➝ fever, headache, muscle pains, nausea, vomiting, recovery after 4-7 days
• Retinopathy ➝ 1-3 weeks after acute symptoms, conjunctivitis, photophobia, may lead to blindness, death is rare
• Haemorrhagic fever ➝ 2-4 days after febrile phase, melena, hematemesis, petechia, icterus, shock, coma, 50% lethality
• Encephalitis ➝ 1-3 weeks after acute phase, sometimes together with haemorrhagic fever
• Average mortality: 1%

Question 7

Pathology and diagnsosis of Rift valley?

Answer 7

Pathology

• Necrotic hepatitis
• Enlarged, yellow, fragile liver
• Petechial haemorrhages in visceral organs and mucosal surfaces
• Haemorrhagic enteritis in large intestine

Diagnosis

• Virus isolation, RT-PCR
• Serology: ELISA

Question 8

Human treatment and prevention Control of Rift valley?

Answer 8

Human Treatment

• Symptomatic and supportive therapy
• Provide coagulation factors
• Ribavirin can have positive effect

Prevention, Control

• Vaccination of susceptible ruminant in endemic regions

• Mouse brain attenuated vaccine is foetopathogen
• Cell culture attenuated vaccine induces shorter protection
• Maternal antibody protection of lambs/calves
• Repeated vaccination with inactivated vaccine protects for 1 year
• Arthropod control
• Personal protection
• Communicable disease, in Europe control with non-specific methods ➝ restrictions, stamping out
• Prevent introduction: quarantine, serological investigations, tourists

Question 9

Nairobi sheep disease info and epidemiology?

Answer 9

Nairobi Sheep Disease

• Fever, haemorrhagic gastroenteritis and abortion in sheep
• Nairoviridae, Orthonairovirus

Epidemiology

• Occurrence: Middle and East Africa in local breeds (mild disease)
• Vector: Rhipicephalus appendiculatus tick ➝ carry virus for years

Question 10

Pathogenesis and clinical signs of Nairobi sheep disease?

Answer 10

Pathogenesis

1. Infection
2. Viraemia
3. Replicates in all organs and tissues

Clinical signs

• Incubation: 2-5 days
• Fever, dyspnea, depression, mucopurulent nasal discharge, haemorrhagic enteritis
• Abortion, oedema in genital organs
• Shock, death (up to 70-90%)

Question 11

Pathology of Nairobi sheep disease?

Answer 11

Pathology

• Haemorrhagic gastroenteritis
• Haemorrhages in heart
• Enlarged liver, kidneys, spleen, lymph nodes
• Full gall bladder
• Hyperaemic genital organs

Question 12

Diagnosis and prevention of nairobi sheep disease?

Answer 12

Diagnosis

• Occurrence, epizootiology
• Clinical signs, pathology
• Direct virus detection ➝ Isolation, IF, AGID
• Indirect virus detection ➝ VN

Prevention

• Tick control
• Vaccination in endemic areas: attenuated, residual virulence, risk of reversion
• Zoonosis ➝ mild fever, general symptoms