The presentation by UK health specialist Fiona Lovatt at last week’s Teagasc sheep conference left those attending in no doubt to the importance of facing up to a new wave of hidden diseases. She said that so called iceberg diseases such as OPA, CLA, Ovine Johne's and Maedi Visna were becoming more commonly diagnosed in the UK and represent a similar threat to Irish producers.
The presentation by UK health specialist Fiona Lovatt at last week’s Teagasc sheep conference left those attending in no doubt to the importance of facing up to a new wave of hidden diseases.
She said that so called iceberg diseases such as OPA, CLA, Ovine Johne's and Maedi Visna were becoming more commonly diagnosed in the UK and represent a similar threat to Irish producers.
The reason the diseases are included under the term of iceberg diseases is due to the high number of undiagnosed cases and small number of clinical cases failing to represent the severity of the problem.
The diseases are all hard to diagnose, partly due to a slow, deceptive onset and absence of simple and accurate testing procedures, but can have significant production-limiting consequences in a flock.
UK health specialist Fiona Lovatt.
For example, the disease Ovine Pulmonary Adenocarcinoma (OPA) caused by Jaagsiekte sheep retrovirus has been on the rise in pockets of the country but the true prevalence is not known.
The difficulty is a readily available accurate method of diagnosis, with Fiona explaining that extensive research has been undertaken in the Moredun research centre in Scotland but has yet to yield positive results.
A recent large-scale study of the lungs of over 1,900 sheep identified 1.6% prevalence, with cases in Donegal, Kerry, Kilkenny, Offaly, Tipperary, Waterford and Wicklow. The study estimates that the prevalence in Ireland is likely to be in line with the UK where there is a high prevalence in geographical regions.
Symptoms
The symptoms are an increased respiratory rate, with sheep possessing a soft cough in the early stages of the disease.
This can progress to increased respiratory problems and sheep coming under pressure when flocked and exhibiting a frothy fluid discharge from their nostrils when their head is down.
This stems from cancer in the lungs with the incubation time generally three years but anywhere from two months to 11 years depending on the severity of the infection.
A secondary bacterial pneumonia can also develop and is more common in affected flocks.
Fiona says the disease can be spread through a number of avenues and the virus is capable of lasting weeks in the environment. It can be spread by respiratory aerosol and contaminated troughs and water while it can also spread to progeny via milk or colostrum.
There is no immune response so blood serology is therefore not an avenue of identification. Fiona says that PCR is possible in the respiratory and peripheral blood lymphocytes but this is not commercially available and even if it was it is not always accurate as it has low sensitivity and virus levels can fluctuate.
Thoracic ultrasound can also be used to identify infected animals but again this method has shortfalls because lesions of greater than 2cm are required on the surface of the lung.
The limited avenues of identification make the disease hard to control. Suspect cases should be explored with infected ewes and their offspring culled.
Where present in a flock, housing single age animals can help to limit its spread. Taking newborn lambs immediately from ewes has been shown to be an option and could be used for high-value animals. Management is also an important consideration.
Stocking density and feeding management should be tailored to reducing close contact between animals.
Read more
Sheep welfare scheme deadline extended
First confirmation of Jaagsiekte retrovirus in Irish sheep
Information on the other diseases listed will be covered in next week's edition.
This is a subscriber-only article
SHARING OPTIONS: