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Spiking Mortality Syndrome Of Turkeys

by 5m Editor
1 January 2008, at 12:00am

Dr John Schleifer of Hoechst Roussel Vet wrote this article for the Alberta Government's Agriculture and Rural Development department in 1996.

History

Spiking mortality syndrome in turkeys has a very short yet complicated history. The reason it is short is that the syndrome was first identified in 1991. However, since then a number of different possible causes have been identified. Yet, the identification of a single disease producing agent has remained elusive.

Most of the investigative work has been performed by researchers and diagnosticians at North Carolina State University. Dr. John Barnes has noted that in 1991, spiking mortality occurred sporadically and seemed to remain localized in certain regions in the mid-Atlantic states of the US. In the spring of 1994 the incidence of the syndrome took a turn for the worse and outbreaks were observed throughout most of the Eastern US. Since then the outbreaks have been variable, with some areas more widely affected than others. Dr. Barnes stated "the syndrome has been extremely devastating. In areas where the disease first started, individual farmers are losing their farms and companies are experiencing tremendous financial difficulties as a result of the problem."

Classification

As of this writing the syndrome has been described as poult enteritis - mortality syndrome. The syndrome has then been classified with two manifestations. The first being, excess mortality of turkeys. This form is characterized as mortality between two to nine percent during a three week period, and does not exceed one percent per day for three days. The more severe form is defined as SMT (spiking mortality of turkeys). This form is defined as mortality exceeding one percent per day for at least three consecutive days. Some flocks with SMT are reported to have mortality levels exceeding 50%. In one case, the mortality level approached 100%.

Symptoms

The syndrome appears to occur most commonly in the summer months. Poults two to four weeks of age seem to most affected. These birds often exhibit a brown flocculant diarrhoea and become unthrifty. Feed refusal accompanies the diarrhea and a stunting syndrome occurs. Of course mortality is the most common indicator of the syndrome. However, the stunting will remain with the surviving birds for the rest of the production phase.

Other lesions include dehydration, muscle loss, poor feathering, thin-weak intestinal conditions, and gas-filled intestines. Studies have concluded that a major component of SMT is a sudden and severe intestinal disease which is accompanied by immune and endocrine organ involvement. It has been observed that surviving birds are not only stunted but they have long-term immune suppression.

Causative Agents

The most significant complication with SMT is that a number of different disease agents are connected with the syndrome.

Work conducted at North Carolina State University has indicated that some of the cases have been associated with Highlands J alpha virus. In the early 1990s, this virus was associated with an epidemic of egg production problems in turkey breeders throughout many parts of the US. A spiking mortality problem has been noted in progeny from turkey breeders that were identified as harboring the Highlands J alpha virus. This virus is related to the eastern and western equine encephalitis viruses. In experimental work and the University of Georgia, the Eastern equine encephalitis virus was able to produce high mortality levels in experimentally infected turkey poults. In these studies, adult turkeys remained resistant to the disease.

Researchers at Ohio State University have reproduced an enteritis and stunting syndrome in turkey poults. A virus was classified as an enterovirus and was isolated from poults exhibiting diarrhea with ballooning of the intestines. When the virus was isolated and reintroduced into disease-free poults, the disease was reproduced.

Researchers at Iowa State University have reproduced a similar diarrhea and stunting syndrome with an isolated astrovirus. Studies with this virus have indicated that the virus does not produce as severe a level of enteritis.

Sentinel work conducted in the Southeast US has resulted in the isolation of a coronavirus. Challenge studies with the virus have been inconclusive. The cases with some of the most excessive levels of mortality, have resulted in the isolation of a coronavirus. A similar coronavirus has been isolated from cattle on affected farms. Coronavirus in cattle causes infectious bovine rhinotracheitis. Some researchers think that there is a link between high cattle density on turkey farms and outbreaks of the disease.

Another researcher from North Carolina State University reported that the cryptosporidia parasite may have a role. This parasite has been isolated from the intestines of many birds from severely affected farms. The significance of this finding remains unknown.

December 2008