Mycoplasmas - Old diseases, new problems

Old diseases have a habit of re-emerging and showing up the holes in our biosecurity procedures. Mycoplasmas are no exception. Having been around for the last 100 years, they still have the capacity to cause chronic respiratory disease (CRD) in chickens, infectious sinusitis (puffy faces) and leg problems in broilers, layers and especially turkeys. Although predominantly diseases of chickens and turkeys, mycoplasmas can infect a number of avian species including game birds, pigeons and other wild birds, which may be significant in the spread of infection to commercial poultry.

Mycoplasmas appear to be very contagious and effective control of the more pathogenic (disease causing) types has been a fundamental stepping stone to improved performance and productivity in the poultry industry. There is evidence that certain mycoplasmas are making a bit of a comeback, sometimes with renewed vigour or virulence and sometimes capable of causing significant financial loss.

There are four main mycoplasmas of commercial poultry:

Mycoplasma gallisepticum (MG)

Mycoplasma synoviae (MS)

Mycoplasma meleagridis (MM)

Mycoplasma iowae (MI)

Fortunately, two of these don’t seem to affect chickens so we are left with MG and MS as the potential bugs that may attack your layers.

Mycoplasma gallisepticum (MG)

This mycoplasma has the ability to cause respiratory disease seen as puffy faces, runny eyes and head shaking. Coughing and sneezing may also be seen. Death is usually related to secondary coli infection, air sac damage and peritonitis. Subclinical (quiet) infection is probably tickled up by a number of other respiratory bugs. MG infection needs to be differentiated from other respiratory viral infections such as IB, ILT and, more recently, avian pneumovirus (causing ART or TRT). MG infection can be confirmed by specific blood test and frequently requires antibiotic treatment to bring about a clinical recovery.

Mycoplasma synoviae (MS)

MS, on the other hand, can infect birds without them showing any clinical signs or effect on production or egg quality. Often the only way you know you have infection in your flock is when a blood test proves positive. The text book shows that MS infection can cause swellings of the leg joints and mild damage to the air sacs leading to low grade respiratory problems. It seems there are big differences between strains of MS in their ability to cause disease problems, and they may need other diseases or trigger factors to cause any clinical harm to your birds or their egg production.

At present, it seems that most of the detected MS infection in commercial layers is "silent" and not associated with disease unless there are significant problems with air quality or simultaneous infection with other diseases.

However, the fact that infection is so widespread is a warning that we all have problems with maintaining our site biosecurity. Mycoplasmas are not thought to survive well outside the bird, so are unlikely to persist on single age sites. Our multiage, continuous production sites are the problem. There are specific treatments that can be used to help control infection, via feed or water, but exclusion is the key.

Keeping diseases out – effective biosecurity – would be a separate topic for a future issue of The Ranger. Until then, the story is the same as it is for so many diseases. Effective monitoring using blood tests and good use of eyes and ears in assessing the health of your flocks throughout their life will allow you to identify which diseases are present and what effect they are having . A real case of knowing your enemy!