| Abstract
|
:
|
Stunting syndrome is an enteric disease of turkey poults with unknown etiology. The objective of present study was to determine the etiologic agent(s) of SS. It was hypothesized that the intestinal epithelial cells (IELs) are infected during the disease. IECs, isolated from SS infected poults at 4 days post inoculation (PI), when inoculated to day-old susceptible poults produced the disease on the basis of reduction in weight gain and intestinal maltase activity. Following lysis of IECs, the 0.2 and 0.1 mum filtrates produced the disease. Fractions collected following density gradient ultracentrifugation (using accudenz) were infectious for day-old poults. Direct examination of these fractions and IECs lysate filtrate (0.1 mum) revealed enveloped, pleomorphic particles ranging in size from 65-95 nm and were termed stunting syndrome agent (SSA). In an attempt to isolate SSA, a cell culture system was developed whereby, turkey IECs were cultured in vitro using intestinal fibroblasts as a feeder layer. The primary cultures of IECs supported the growth of SSA. Attempts to grow SSA in chicken (amniotic, allantoic, choroallantoic membranes, yolk sac), turkey (chorioallantoic membranes, allantoic, yolk sac), and primary and continuous cells were unsuccessful. However, inoculation of 24-to-25-day-old turkey embryos via the amniotic cavity resulted in SSA replication. The infection in embryos resulted in enteric lesions (pale, thin intestine filled with fluid), reduced intestinal maltase activity, reduced D-xylose absorption. The intestinal fluid contained SSA. The relatedness of SSA to other mammalian and avian viruses was determined using avidin-biotin enhanced ELISA, serum virus neutralization, and RT-PCR. Based on these assays, the SSA was distinct from turkey coronavirus (bluecomb disease agent), bovine coronavirus (Nebraska calf diarrhea virus), transmissible gastroenteritis virus, bovine breda-1 virus, bovine breda-2 virus, avian infectious bronchitis virus (Massachusetts strain), Newcastle disease virus, and avian influenza virus. Studies on the physico-chemical properties revealed that SSA was sensitive to ether but was resistant to proteolytic enzymes (trypsin, pancreatin, pepsin), sodium deoxycholate, and phospholipase C. Treatment with proteolytic enzymes resulted in increased viral infectivity. SSA was also resistant to pH changes between 3.0 and 9.0. SSA has a single stranded RNA genome. These characteristics are consistent with an enteric virus. From these studies, it was concluded that the SSA causes SS in turkey poults and is a newly identified but unclassified viral agent.
|