Reovirus PDF

REOVIRUS Reoviruses were first recognized as avian pathogens in 1957. This first case was from chickens showing clinical signs of what became known as viral arthritis (VA). Since that time reoviruses have become associated with other disease conditions including malabsorption syndrome (MAS), femoral...

REOVIRUS Reoviruses were first recognized as avian pathogens in 1957. This first case was from chickens showing clinical signs of what became known as viral arthritis (VA). Since that time reoviruses have become associated with other disease conditions including malabsorption syndrome (MAS), femoral head necrosis (FHN), pericarditis, myocarditis, hydropericardium, gastroenteritis, hepatitis, and acute and chronic respiratory syndromes. - Reoviruses are double-stranded RNA viruses and are highly resistant to both physical and chemical inactivation, as well as low pH. - These viruses are very similar to Infectious Bursal Disease Virus and are similarly resistant to many common disinfectants. - Reoviruses will remain infective in contaminated environments for long periods of time. When held in a culture, reoviruses remained viable for almost a year when held at 72°F. In a management system that allows for a two week turn around time on built-up litter, the effect on the reovirus population would be minimal. - Reovirus has been shown to cause an inflammation within tendons that may result in a reduction in these tendons tensil strength. Inflammation, due to reovirus, may develop in a joint resulting in arthritis or within a tendon sheath resulting in tenosynovitis. In broilers, roasters and breeders, this results in lameness and stunting. This is often not seen until after five weeks of age. - Reoviruses have been associated with a syndrome of nutrient malabsorption that result in poor growth and skeletal abnormalities. This lack of utilization of provided nutrients has been related to intestinal, pancreatic and/or liver abnormalities. Diseases associated with reoviruses have been reported in both heavy and light breeds of chickens. Heavy breeds are more susceptible to disease associated with tendons (viral arthritis). This is probably due to two reasons: 1. Large, meat-type birds grow rapidly, resulting in physical changes to the load-bearing leg tendons. This may predispose birds to infection. Leg tendons in broilers also have less tensile strength and a more open structure which is more conducive to infectious agents. 2. Broiler breeds take approximately one week longer to respond serologically to reovirus infections. This delay in immune response may contribute to the greater susceptibility of the heavy breeds compared with lighter breeds. - Reovirus-associated viral arthritis is seen more frequently in males than females. Other than increased susceptibility in broiler-type birds, there is no scientific evidence of increased incidence in specific heavy breeds. Economic impact: - Reovirus-associated disease having an economic impact on the worldwide poultry industry are viral arthritis (VA), malabsorption syndrome (MAS), brittle bone (BB), and femoral head necrosis (FHN). - Tenosynovitis is clinically observed in young chickens (five to eight weeks of age) and mature breeders (over 20 weeks of age after onset of production). The clinical disease in the five to eight- week-old group results in higher mortality and lower grade broilers/roosters.  - When breeders break down, the losses are due to excessive culling due to lameness and lowered fertility (reduced desire to mate due to sore legs). - MAS is most commonly associated with birds 7 to 21 days of age. High mortality is seldom seen; however, poor feed conversions and decreased marketability are common. - Transient immunodepression: Selected reoviruses are capable of causing a transient immunodepression. Pathogenic reoviruses in young birds have been shown to cause bursal lymphoid depletion lasting as long as 11 days. (There was also a similar depletion in the thymus.) This resulted in a decreased response to Newcastle disease vaccination as seen on serology and challenge results. SEROTYPES - There are hundreds of reoviruses that have been isolated and at this point, it is not possible to group them into distinct serotype categories. - Reoviruses differ in their ability to cause disease as well as their ability to cross protect. - Several strains have been categorized as exhibiting low, intermediate, and high pathogenicity when introduced into unprotected broilers. - In general, the viruses that were classified as being more pathogenic produced higher mortality rates, lower average body weights and induced a more consistent antibody response than did the less pathogenic reovirus isolates.  Runting-Stunting Syndrome in Broilers Malabsorption syndrome, brittle bone disease, infectious proventriculitis, helicopter disease Introduction RSS continues to cause economic hardship in the broiler industry through decreased body weights, elevated feed conversions, reduced uniformity, reduced livability, plant downgrades and secondary diseases Etiology: Researchers have not reproduced all the field symptoms of RSS experimentally and believe that several viruses, bacteria and other pathogens may be involved. Reovirus was originally thought to be the cause of RSS, but adenovirus, enterovirus, rotavirus, parvovirus and others may also be involved. Bacteria often isolated from RSS birds (E. coli, Proteus micabilis, Enterococcus faecium, Staphylococcus cohnii, Clostridium perfringes, Bacteroides fragilis and Bacillus licheniformis) are commonly found in the intestinal tract and may cause secondary infections, aggravating the initial lesions Diagnosis and differential diagnosis: While symptoms of RSS can vary dramatically, birds are generally affected by RSS early in life with symptoms and mortality peaking at about 11 days. - After placement, RSS affected birds may huddle around feeders and waterers, or may persistently peck at the walls. Feed consumption is often depressed. A sizable proportion of the flock may be involved and while affected birds that are not culled may not die, they never recover. Often flock mortality is unaffected, but  - Flock uniformity which normally runs about 70% decreases to about 35%. As feathers appear on affected birds, they are smaller than normal and may be curled especially at the wing tips (helicopter disease) (Zavala, 2006). The legs and beak of affected birds may appear, pale in color (pale bird syndrome) and some Lesions: - Birds may have rickets or broken legs (brittle bone disease) When diseased birds are necropsied, the livers are generally small, but gall bladders are enlarged. Intestines are thin and translucent with large amounts of fluids along with poorly digested feed present in the - Intestines of affected birds may appear enlarged whereas the stomachs (proventriculi) may appear inflamed, The normal intestinal growth of the jejunum (the portion of the intestine where much of the digestion and nutrient absorption takes place) is interrupted by RSS - Pancreases from diseased birds degenerate and digestive enzymes are reduced. Droppings from affected birds are unusually loose, vents are soiled and litter may become damp, enhancing the possibility of secondary Prevention and control: RSS often appears suddenly and disappears equally suddenly, making it difficult To determine effective control measures. However, it is important to remember that RSS is a disease of young birds with symptoms and mortality peaking at about 11 days so control efforts should be focused early in the life of the flock. Control efforts should focus in three primary areas: Biosecurity, Good poultry house and management and vaccination. When RSS is reported in an area, it is important for the industry in the area to tighten Biosecurity procedures to reduce the possibility of exposure and to slow the spread of the disease. - Control farm visitors, properly manage disposal of mortality and limit vermin infestations (rodents, wild birds and insects). - The objective of proper poultry house management is to provide an environment for the birds that is virtually stress free. - In RSS situations, poultry house management is doubly important. Good management starts before the birds arrive. A minimum of 12 days of downtime should be allowed between flocks. Since litter has been shown to transmit the disease, it should be removed if birds have broken with RSS - The brood chamber should be cleaned and disinfected as thoroughly as possible prior to chick placement - Check on birds often and maintain a house environment that is as stress free aspossible. - Remove dead birds quickly and cull severely if RSS breaks. The application of vinegar or other acidifiers via water may reduce spread of the disease. - Supplemental vitamins and minerals in both breeder and broiler feeds has also been shown to improve immunity in chicks and their ability to deal with RSS. VACCINATION - Vaccination for reovirus is widely practiced. Protection is achieved through maternal antibodies followed by vaccination, if needed. - Maternal antibodies last a variable amount of time, depending on the hen’s titer when laying the egg. The goal should be for maternal antibodies to be present through the first week of life, the most susceptible time period. - When maternal antibodies are virtually depleted, a highly attenuated vaccine can be given at this time. This often occurs between 7 and 14 days. Protection from challenge can be expected to last five to six weeks. - PRIMING the two vaccinations described act as an excellent prime to the immune system for eventual boosting of breeders. Since all reoviruses are related to the S1133 strains of reovirus, this strain works well as the priming antigen. - BOOSTING Breeders are often given an inactivated vaccine four weeks prior to the onset of egg production. This further boosts their titer to increase protection to progeny. It has the added advantage of decreasing the risk of vertical transmission of the virus.