So-called because the whole eye develops a bluish tinge as a result of corneal opacity).
Blue eye disease (BE) is characterised by clinical signs of nervous derangement, reproductive problems and opacity of the surface of the eyes (corneal opacity). It is thought to be caused by a paramyxovirus.
Should you be concerned about blue eye disease (BE)?
BE was first recognised in central Mexico in 1980 and was later diagnosed in many other regions of Mexico. If you are involved in pig farming in Mexico, you should be concerned about it.
It has never been diagnosed in any other countries and is unlikely to spread to them.
In Japan, a paramyxovirus (the Sendai virus) can cause nervous disorders and reproductive problems but it is probably a different virus.
If you are involved with pig farming outside Mexico and your country has strict controls over imports of live pigs, particularly from Mexico, do not be concerned.
But beware! You could confuse ontario encephalitis (the nervous form of vomiting and wasting disease) which occurs in Europe and North America with it.
When the disease first breaks out in a susceptible breeding herd the first clinical signs are usually seen in the farrowing house. Piglets are hunched with rough coats for a short time and then suddenly develop acute nervous signs. They have difficulty walking, start to shiver, and sit in abnormal postures. Some lie on their sides, paddle their legs and roll their eyeballs back and forth. The eyes of some piglets water and the eyelids swell and get stuck together. Worst affected are piglets under 2 weeks of age. Up to 90% die. Older weaned piglets may develop blueing of the pupils (black centres) of the eyes. Up to 65% of litters may be affected. The disease disappears slowly and spontaneously after several weeks.
Older pigs of a month or more in age show milder transient signs of loss of appetite, fever, sneezing and coughing. Nervous signs, such as an unsteady walk, are less common.
Some adult pigs also show clinical signs including blueing of the eyes. There is an increased return rate in sows lasting about 6 months. Abortions and stillbirths may occur. Up to 40% of boars have testicular enlargement, which is usually one-sided, followed by shrinking with a concurrent loss of fertility.
In acute severe outbreaks a strong presumptive diagnosis can be made based on the nervous signs, corneal opacity, infertility and testicle changes.
For confirmation of the presumptive diagnosis serological tests have to be done in the laboratory. Virus isolation from brain tissue can also be demonstrated.
There are no lesions indicative of BE that can be seen with the naked eye.
Diseases with similar clinical signs include aujeszky’s disease (AD), PRRS, ontario encephalitis (vomiting and wasting disease), and brucellosis. However, none of them have all the clinical signs of BE.
- There is no effective treatment.
Management control and prevention
- Vaccination – This should be a useful method if and when an effective vaccine is developed.
- Biosecurity – This should reduce the chances of your herd being infected. Read the final section of this chapter.
- On-farm eradication – Once a herd has been infected and clinical signs have disappeared the virus may disappear. To help this do not introduce replacement stock into the herd for 1 – 2 months.