Test 3- Reoviridae Flashcards
General Properties of Reoviruses
- Virions are nonenveloped, nearly spherical in outline, 70-80nm in diameter.
- Mature viral particles are composed of 3 concentric layers (the Outer,Intermediate/Middle and Inner layers), outer layer has icosahedral symmetry(T=13).
- The viral genome is composed of segmented double-stranded RNA (dsRNA). Number of dsRNA segments range from 10-12 segments depending upon the genus.
Viral replication occurs
Viral replication occurs in the cytoplasm
General Properties of Reoviruses
- Genetic reassortment
- Genetic reassortment occurs between viruses within a genus or serogroup.
because they have double stranded RNA- they are very likely to reassort
BLUE TONGUE- HOSTS and generals
(Sore Muzzle, Pseudo Foot-and-Mouth, Ovine Catarrhal Fever, Muzzle Disease)
Bluetongue is an infectious, non-contagious, insect-borne disease of domestic and wild ruminants caused by the Bluetongue (BTV) virus, a member of the genus Orbivirus.
Most Susceptible/Common Hosts: Sheep (particularly fine wool & mutton breeds that are common in Europe) and some species of Deer, such as White-Tailed Deer, are most susceptible to BTV and exhibit severe form of the disease.
Inapparent infection: Cattle, Goats and some Wild Ruminants.
Cattle are the primary reservoir and amplifying host in most areas and have a high titer Viremia.
Impact of Bluetongue (BTV)
Bluetongue is a “List A” disease of the Office of International Epizootics (OIE). List A diseases are Transmissible diseases that have the potential for very serious and rapid spread, irrespective of national borders, that are of serious socio-economic or public health consequence and that are of major importance in the international trade of animals and animal products.
REPORTABLE DISEASE
Examples of Economic Impact of BTV:
Since its arrival in Europe in 1998, BTV has caused the deaths of > 1 million sheep.
Worldwide economic losses associated with BTV in 1996 exceeded 3 billion US dollars .
In addition to morbidity and mortality, imposition of strict trade regulations to export animals and their germ-plasm from BT-affected nations to BT-free countries significantly impacts the economy. The U. S. losses in trade and associated testing for BTV status has been estimated at $144 million annually.
Etiology of Bluetongue
Ovine Orbivirus:
Bluetongue virus (BTV) belongs to the genus Orbivirus in the family Reoviridae. The BTV genome consists of ten segments of double-stranded RNA (dsRNA).
Antigenic differences of outer shell proteins between different BTV strains form basis of classification of BTV into different serotypes.
BTV are classified into at least 26 serotypes so far.
In US 2, 10, 11,17, and 13
Transmission of BTV
Arthropod (Insect)-borne transmission (Major route of transmission)
Transmitted biologically by certain species of Culicoides, a genus of biting midge.
In USA, Culicoides variipennis var sonorensis is the vector, except in Southeast where it is C. insignis.
Less significant routes of Transmission:
Trans-placental transmission has been reported in cattle and sheep.
Venereal Transmission: BTV virus has been found in semen of infected bulls and infection has been transmitted through bull semen to susceptible cows.
Pathology of BTV in Sheep
Damage to Vascular Endothelium
Intravascular Coagulation
Necrosis of tissues and organs supplied by damaged capillaries
Edema
Hemorrhage
Congestion
Abortion (Abortive form of BTV disease in enzootic areas)
CNS malformations
Clinical Findings of BTV in Sheep
Profuse Salivation, Edema of muzzle, Reddening of nasal mucosae
Mucopurulent nasal discharge, often blood stained. Crust formation on Nostrils and Lips
Linear erosion and reddening of the buccal mucosa.
Cyanosis, necrotic ulceration of tongue (Hence the name BlueTongue)
Erosion of Dental Pad, Necrosis, Hyperemia, Ulceration in Oral Cavity
Coronitis and Laminitis causing Lameness
Extensive Facial Swelling
Erosions in the buccal cavity, drooling of Saliva
Aborted, macerated fetuses
Hemorrhage and Congestion of Muzzle
Serous to mucopurulent nasal discharge, Erosions on the muzzle with sloughing of the mucosa
Ulcerative Glossitis and Stomatitis
Ulceration of Teats
Lachrymation, hyperemia and edema of Conjunctiva
Coronitis and Lameness
Diagnosis of BTV
Clinical signs
Virus Isolation: By tissue culture or in developing chick embryos
Detection of Antigen: Immunohistochemical tests, such as Immunofluorescence, Immunoperoxidase tests.
Detection of Nucleic Acid: Polymerase Chain Reaction (PCR)
Detection of Antibody: Agar Gel Immunodiffusion test (AGID), Competitive ELISA
Necropsy Findings, Histology
Prevention of BTV
Vaccination: Attenuated vaccines, which are available in countries including the U.S., are generally serotype specific.
Vector control: Use of Repellents and Insecticides, lodging animals indoors during night since Culicoides have nocturnal feeding habits, using nets in windows and doors of animal shelters, not allowing animals to graze near possible insect breeding areas.
African Horse Sickness (AHS) generals
Infectious, non-contagious, arthropod-borne disease of horses, donkeys, and mules.
Mortality rate of 75-90% in horses.
Dogs sometimes contract a highly fatal form of AHS, resulted from the ingestion of infected carcass material from horses that have died from AHS.
“List A Infectious Diseases” of the OIE. Enzootic in sub-Saharan Africa, although occasional outbreaks have occurred in Northern Africa, Middle East and in Europe.
ETIOLOGY OF AHS
Caused by a virus belonging to Genus Orbivirus( has 10 segments of ds RNA) .
At least Nine Antigenic Serotypes of AHS virus have been reported so far, based on variations in outer capsid protein VP2 and to a lesser extent VP5 proteins
Transmission and Pathogenesis of AHS
Transmitted by Culicoides species that occurs regularly in most countries of sub-Saharan Africa. At least two field vectors are involved: Culicoides imicola and C. bolitinos.
Healthy Horse bitten by Culicoides and become infected.
Pathogenesis is same as Bluetongue in Sheep.\
Inapparently Infected, reservior- Zebras
