Lesson 25: Reoviridae

Question 1

The family Reoviridae derives its name from the prototype virus which was
known as the

Answer 1

Respiratory enteric orphan virus

Question 2

Virus in the family reoviridae are icosahedral, 60 to 80nm in diameter, nonenveloped and possess a layered capsid which is composed of concentric
protein shells.
 The genome of reoviruses is composed of ten to twelve segments of doublestranded RNA.
 Replication takes place with the cytoplasm of the host cell often with the
formation of intracytoplasmic inclusions.
 They are originally isolated from respiratory and enteric sources without any
clinical condition and were thus named orphan.

Question 3

are arthropod-borne viruses that cause African horse
sickness in horses and blue tongue in sheep and in other domestic and
wild ruminants

Answer 3

Orbivirus members

Question 4

causes enteritis in neonatal farm animals

Answer 4

Rotavirus

Question 5

causes arthritis and tenosynovitis in poultry

Answer 5

Orthoreovirus

Question 6

primarily infect rodents and human
but occasionally cause clinical disease in domestic animals

Answer 6

Coltivirus (Colorado tick fever virus)

Question 7

Reoviruses are moderately resistant to heat, organic solvents and non-ionic
detergents.

Question 8

Orthoreoviruses and rotaviruses are stable over a wide range of pH values while
orbiviruses lose infectivity at low pH values

Question 9

 This disease is a non-contagious viral disease of sheep and other domestic and
wild ruminants caused by serotypes of bluetongue virus (BTV) in the genus
orbivirus of the family Reoviridae.

Answer 9

BLUETONGUE

Question 10

There are 26 serotypes known, with each strain having variable disease severity.
 BTV-25, 26 and 27 spread exclusively through vector-independent routes,
potentially causing persistent goat infections.
 In endemic areas, infection of cattle is common and usually inapparent. The
viraemia in cattle commonly lasts several weeks facilitating transmission of the
virus to susceptible host by the insect vector.
 Cattle are considered to be important reservoir of the virus

Answer 10

Bluetongue

Question 11

Transmission of Bluetongue??

Answer 11

 The disease is transmitted by Culicoides imicola in Africa and Asia.
 Venereal transmission through the semen of ram and bull has been reported.
 It can also be transmitted by embryo transfer.

Question 12

Clinical signs of bluetongue??

Answer 12

fever, depression, lip congestion,
oedema, oral mucosa erosion, excessive salivation, tongue lameness,
tortocillis, abortion, and mortality up to 30%.

Question 13

Diagnosis of Bluetongue??

Answer 13

 Clinical signs and postmortem findings are suggestive
 Laboratory confirmation requires isolation and identification of the virus or
demonstration of BTV-specific antibodies
 Samples: unclotted blood from febrile animals or fresh spleen and lymph
node collected at post mortem
 Virus isolation in embryonated egg inoculated intravenously
 Antigen detection by ELISA
 Serological test for detecting antibodies to BTV serotypes using Complement
fixation test, Agal gel immunodiffusion, indirect immunofluorescence and
competitive ELISA

Question 14

Control of Bluetongue

Answer 14

attenuated vaccine for protection against virulent virus of homologous
serotype
-Live attenuated vaccine may be teratogenic when used in pregnant
animals during the first half of gestation
-Live attenuated vaccine should not be used during the period of high
vector activity because of the possibility of transferring the vaccine virus to
pregnant animals and the possible genetic reassortment with field virus.
-Live attenuated vaccine virus may revert to virulence
 Polyvalent vaccine in regions where more than one serotype is prevalent
 Killed adjuvanted vaccine can induce protection but requires booster dose. It
is more expensive to produce.
 Recombinant virus-like particle capable of inducing protective immunity have
been produced in insect cells infected with recombinant baculoviruses
expressing BTV protein.

Question 15

is a reportable, noncontagious, nonzoonotic,
arthropod-borne viral disease of equids that is endemic to sub-Saharan Africa.

Answer 15

African horse sickness (AHS)

Question 16

African horse sickness (AHS) is a reportable, noncontagious, nonzoonotic,
arthropod-borne viral disease of equids that is endemic to sub-Saharan Africa.
 It can be acute, subacute, or subclinical and is characterized by clinical signs
and lesions associated with respiratory and circulatory impairment.
 The African horse sickness subgroup is made up of nine serotypes of AHSV and
they are distinguishable by neutralization tests.
 Horses are the most susceptible equids, with AHSV infection potentially leading
to case fatality rates of up to 90% in naive populations

Question 17

African horse sickness(AHS) transmitted by

Answer 17

haematophagous insects

Question 18

The major vector of African Horse Sickness (AHS)

Answer 18

Culicoides inicola

Question 19

CLINICAL SIGNS OF AFRICAN HORSE SICKNESS


Answer 19

Fever and mucous membrane congestion are normally the initial clinical
signs, followed a few days later by the supraorbital swelling and
subcutaneous edema of the head and neck.

Question 20

Four clinical forms of African Horse Sicknesses (AHS )are recognized:

Answer 20

1. Peracute pulmonary form - Characterized by depression, nasal discharge
   with rapid progression to severe respiratory distress.
2. Subacute cardiac form - Conjunctivitis, abdominal pain and progressive
   dyspnoea
3. A combination of pulmonary and cardiac features
4. Mild or subclassical form termed horse sickness fever observed in zebra
   and donkeys

Question 21

DIAGNOSIS OF AHS

Answer 21

 Provisional diagnosis based on clinicopathologic findings
 Definitive diagnosis is made by agent identification to rule out differential
diagnoses
 EDTA-anticoagulated whole blood or fresh spleen and lung on ice are samples
of choice
 Confirmation best by OIE-validated real-time PCR assay

Question 22

PREVENTION AND CONTROL OF AHS

Answer 22

 Currently, there is no specific curative treatment for animals with AHS except for
supportive treatment aimed at cardiac and pulmonary support, rest, and good
general husbandry
 Prevention by vaccination remains the mainstay for control in endemic countries
 Equine movement control to prevent incursion into free areas and spread within
endemic areas
 Vector control and protection of equids

Question 23

is caused by a virus of the family
Reoviridae, genus Orbivirus; there are 8 or more serotypes and Ibaraki virus is a
member of the EHD virus (EHDV) serogroup (serotype 2).

Answer 23

Epizootic haemorrhagic disease (EHD)

Question 24

was considered an emerging disease in cattle, and was added to OIE list of
notifiable diseases in May 2008, following outbreaks in four Mediterranean
countries

Answer 24

(EHD) EPIZOOTIC HAEMORRHAGIC DISEASE

Question 25

demonstrates immunological cross reactivity with the Bluetongue virus
group.

Answer 25

Epizootic Haemorrhagic Disease Virus

Question 26

(EHD )EPIZOOTIC HAEMORRHAGIC DISEASE can infect most wild and domestic ruminants
 Virus is transmitted by biological vectors, usually biting midges of the genus
Culicoides, after an external extrinsic period of 10–14 days
 In temperate regions infection is most common in the late summer and autumn
during peak vector population, while infection occurs throughout the year in
tropical regions

Question 27

CLINICAL SIGNS OF EPIZOOTIC HAEMORRHAGIC DISEASE

Answer 27

 The clinical signs of EHD manifest as haemorrhagic disease in deer, but
domestic ruminants may be subclinically infected.
 Acute EHD in deer: Fever, weakness, inappetence, excessive salivation,
facial oedema, hyperaemia of the conjunctivae and mucous membranes
of the oral cavity, coronitis stomatitis, and excessive salivation
 In prolonged cases, oral ulcers on the dental pad, hard palate, and
tongue may occur. Excessive bleeding occurs in fulminant disease:
bloody diarrhoea, haematuria, dehydration, and death
 Ibaraki disease in cattle is characterized by fever, anorexia and difficulty
swallowing
 Abortions and stillbirths have also been reported in some epidemics.
Some affected cattle die (up to 10%)

Question 28

DIAGNOSIS OF EPIZOOTIC HAEMORRHAGIC DISEASE
 Virus isolation and detection in;
 Whole blood in EDTA and/or heparin (virus isolation), in EDTA or
citrate (PCR)
 Spleen
 Lungs
 Lymph nodes
 Liver
 Serological tests

Question 29

PREVENTION AND CONTROL OF EPIZOOTIC HAEMORRHAGIC DISEASE

Answer 29

 Other than Ibaraki in cattle, treatment and control is limited for EHDV
 Protect animals during loading and transport operations, both by air and
land, through physical barriers, insect repellents and planning of
operations for low vector activity times of the day
 Management of Culicoides breeding areas near cattle hosting facilities
 Both live modified and inactivated vaccines have been developed to
control Ibaraki disease in cattle in Japan