Turkey rhinotracheitis, Avian rhinotracheitis, Swollen head syndrome
3. Introduction
Avian pneumoviruses have been implicated in the upper respiratory tract disease of turkeys and chickens known as turkey rhinotracheitis. The virus has also been associated with swollen head syndrome of chickens. First described in south Africa in the late 1970s, avian pneumovirus soon appeared in Europe and the Middle East. The disease has now been reported from all the major poultry-producing areas in the world except for Australasia. The virus has also been detected in pheasants and guinea fowl, and serologic evidence suggests other avian species are susceptible. Recent studies have indicated an antigenic relationship with a newly discovered human pneumovirus isolated from children with respiratory tract disease. Avian pneumoviruses are members of the subfamily Pneumovirinae, belonging to the family Paramyxoviridae. The subfamily consists of 2 genera: Pneumovirus, consisting of mammalian respiratory syncytial viruses and mouse pneumovirus, and Metapneumovirus, in which avian pneumoviruses are placed. Based on observed differences following sequence analysis of the viral genes, at least 3 subtypes of the virus have been described (A, B, C). Subtype C viruses appear to be the only subtype found in North America and have not been reported in other parts of the world (Merck Vet Manual: Avian Pneumovirus).
4. Microbial Pathogenesis
Following infection, the virus is shed from the nares and trachea but not in the feces. After initial introduction of the virus, the disease spreads rapidly within a geographic area or country. The methods by which the virus is spread are unclear and often unpredictable. Direct contact attributed to movement of infected birds, personnel, equipment, and vehicles have all been implicated, while airborne transmission has also been reported to occur. There is no published evidence of vertical transmission via the egg, even though the virus has, on occasion, been detected in the reproductive tract of laying birds. Persistence of the virus in turkeys and chickens has not been demonstrated and, following experimental infection, virus was detected for 6-7 days only after inoculation. Wild birds have been implicated in the spread of avian pneumovirus, particularly waterfowl and gulls (Merck Vet Manual: Avian Pneumovirus).
Vaccination Protocol:
One-week-old SPF poults were arbitrarily separated into four groups of five or six birds. All vaccinations were delivered by syringe injection into the thigh muscle in 0.1-ml aliquots. Control birds received PBS at days 7 and 21 of age. Birds receiving either pCMV, pCMV-F, or pCMV-N received 50 ag of plasmid DNA on day 7 and 100 ag on day 21 (Kapczynski and Sellers, 2003).
Vaccine Immune Response Type:
VO_0000286
Immune Response:
Serum neutralizing antibodies were significantly higher in birds receiving pCMV-F compared with all other groups (Kapczynski and Sellers, 2003).
Challenge Protocol:
Two weeks after the second vaccination, birds were challenged via intranasal route with 1 x 10^5 TCID50 Mn la per bird (Kapczynski and Sellers, 2003).
Efficacy:
Poults receiving pCMV-F had significantly decreased levels of virus in tracheal swabs on all days in Experiment I and on day 7 in Experiment II compared with other groups. In addition, the percentage of birds displaying clinical signs of disease was decreased in turkeys receiving pCMV-F in both experiments. In experiments I and II, only 20% and 30%, respectively, of birds vaccinated with pCMV-F displayed clinical signs at day 7 (Kapczynski and Sellers, 2003).
2. Avian Pneumovirus Modified Live Virus Vaccine (USDA: 1A31.20)
