Anneke Feberwee is a poultry veterinarian and expert in the field of mycoplasma in poultry. She keeps you up to date on the latest developments.
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Mycoplasma Gallisepticum, Mycoplasma Synoviae and Mycoplasma Meleagridis are important pathogenic mycoplasma strains affecting commercial poultry. Mycoplasma is a small bacteria-type pathogen that can cause diseases in poultry.
Mycoplasmosis in poultry is caused by three different mycoplasma strains, namely M. gallisepticum (M.g.), M. synoviae (M.s.) and M. meleagridis (M.m.)
- M. gallisepticum occurs in chickens and turkeys, and mainly causes inflammation of the respiratory system and also laying problems in older animals.
- M. synoviae occurs in chickens and turkeys. Besides strains with affinity for the respiratory system that lead to subclinical infections, there are also strains with affinity for joints and the oviduct. These latter two strains cause particular economic damage. The joint strains cause inflammation in the joints and tendons. The oviduct strain causes eggshell abnormalities (EPS), which can lead to increased breakage and an indirect and direct reduction in egg production.
- M. meleagridis occurs in turkeys and can cause inflammation of the respiratory system, reduced production, skeletal abnormalities (in young animals) and stunted growth.
Mycoplasmas are sensitive to disinfectants and dehydration. They will therefore not survive long in an empty, clean and dry barn.
However, they can survive for days or even weeks when protected by egg remnants or other material. Mycoplasmas are almost impossible to eradicate in a flock of chickens, as the bacteria are present in the respiratory tract and air sacs very soon after chickens become infected. Medication is then insufficiently effective. Treatment of mycoplasmas will therefore never suffice; the flock will remain infected.
Survival in material outside chickens can vary:
Hair: up to 3 days
Nose: up to 1 day
Feathers/dust: 2-4 days
Straw, rubber, cotton: 1-2 days
Egg material: 6-18 weeks
Faeces: 1-14 days
Species of mycoplasma
Mycoplasma gallisepticum (M.g.) is a small, bacterial pathogen that generally causes severe disease in layers and poultry. The severity of the disease depends on the age of the infected animals, the virulence of the M.g. strain and the presence or absence of other infections. An M.g. infection can cause considerable damage in laying flocks, particularly due to reduced egg production and diminished egg quality.
M.g. can be carried via (direct and indirect) contact and from maternal parent stock to their offspring via the egg (vertical transmission).
Infection with M.g. can take place via contact with infected dust, feather or water particles, which infect the chicken via its nose and/or eye mucus membranes. Such particles may come from infected chickens in a flock at the same farm, but equally from animals at some distance from the farm. The infection may also be introduced via infected dust (on clothing and hair), feathers, material contaminated with egg remnants (on trays!), etc. Day-old chicks can be infected by their mother or at the hatchery. They are then (more) sensitive to respiratory problems.
Young chicks almost always become sick when infected with M.g. In the worst case scenario, the chicks will suffer acute pulmonary restriction and may even suffocate. This is particularly the case in combination with an Escherichia coli or Ornithobacterium rhinotracheal (O.r.
) bacterial infection. Such a combined infection often results in a rattling noise. Because the problems tend to re-occur, this disease is commonly referred to as Chronic Respiratory Disease (CRD). Chicks that survive the disease often remain low in weight and have a strong respiratory reaction following vaccination with live viruses. The clinical signs are usually milder in older animals and they may even be asymptomatic. Since 1997, the strains of M.g. detected in the Netherlands are known to also cause audible and visible respiratory problems in adult animals. When animals become infected shortly after the start of egg production, the production volume will generally start 10 to 15 percent lower than average. However, production will then gradually increase to a (near) normal level. Production will regularly drop to 5 percent under the norm when the infection re-emerges or co-infections occur such as Infectious Bronchitis. In very mild infections, the owner will not notice any real difference in the animals, and the disease will only become apparent following blood tests.
M.g. can cause considerable damage in meat turkeys due to stunted weight development, increased losses, costs of medication and higher feed conversion. Following infection, the animals are more sensitive to other respiratory problems. Once an M.g. infection is detected at a meat turkey farm, we advise that the veterinarian establish a control programme, tailored to the farm. An ‘M.g. control programme for meat turkeys’ guide has been drawn up and is available via your veterinarian. Monitoring and prevention of M.g. in breeding animals is covered by EU legislation (Animal Health Regulation, EU 2019/2035). The monitoring of M.g. at layer farms and farms housing meat turkeys is established at the national level in the Rules for animal husbandry, whereby end layer flocks and meat turkey flocks are tested for the presence of M.g. antibodies prior to slaughter.
(M.s.) occurs worldwide. Breeding poultry is not generally infected with this bacteria. There is however a high prevalence in the end product in the Netherlands (layer and meat sector, approximately fifty percent). In commercial poultry farming (chickens and turkeys), M.s. often causes subclinical infections of the respiratory system. The bacteria can also enter joints via the bloodstream, resulting in infectious synovitis, exudative synovitis, tenosynovitis or bursitis. The variation in clinical signs depends on the various M.s. strains. The damage in the case of meat poultry consists of retarded growth and increased losses. Production drops are also seen in layers, and now also arthritis and joint amyloidosis particularly in brown hens.
M.s. is transmitted both vertically and horizontally. Depending on the strain, all contact animals may become infected within one to six weeks, though generally a small number of animals (ten to fifteen percent) will develop infectious synovitis. M.s. does not have a cell wall and is therefore fragile. The bacteria can survive one to three days in feather material, dust and clothing; one to two weeks in faeces and six to eighteen weeks in egg material.
(M.m.) only occurs in turkeys. Due to a multi-year control programme in the reproduction sector, M.m. infections have been considerably reduced worldwide. In Europe, there are organised efforts to combat both M.m. and M.g. in reproduction stock. M.m. can result in respiratory problems and skeletal abnormalities, which may worsen when there is co-infection with for example M.s. The turkey sector in the Netherlands has been free from M.m. for the past 20 years. M.m. antibodies have recently been detected at three meat turkey farms, and M.m. was also isolated at one of these farms. All these cases concerned imported flocks. Additional insight is necessary in order to determine whether these were incidental cases. We must continue to be alert to M.m. when importing meat turkeys.
(M.i.) is isolated in chickens and turkeys. The most important indication for an M.i. infection in turkey breeding stock is increased embryo mortality and a reduced hatching percentage. M.i. can also cause a limited degree of respiratory and foot abnormalities. M.i. is assumed to occur worldwide, though there are no indications that M.i. is to be found in the Netherlands.
Diagnosis of mycoplasma
Detection of antibodies
The bacteria are often difficult to detect due to them ‘hiding’ in the respiratory organs, and detection is relatively time-consuming and expensive. Bacteriological testing is therefore generally not the chosen method of diagnosis; instead serological testing can detect specific antibodies in the blood of infected animals. This is a simple, quick and inexpensive method. Approximately three weeks after infection, there are sufficient antibodies in the blood to detect the presence of M.g., M.s. or M.m. The (sero-)diagnostics are based on the RPA (rapid plate agglutination) test. This test is positive within seven to twenty-one days of infection. The classical confirmation test requires cultivation. This test can take three to four weeks and may even prove negative. GD uses a combination of the RPA test and the ELISA test for serological diagnosis of M.g. and M.s.
The PCR test is important in order to detect infections with M.g. and M.s. (as well as M.m.). In particular, the PCR can detect early infections (prior to antibodies being formed). The PCR is also used as a confirmation test for the cultivation method. A differentiating PCR has been developed for M.s. This PCR distinguishes between the MSH vaccine strain and field strains.
Approach to and prevention of Mycoplasma gallisepticum
A number of measures can prevent problems caused by M.g. infections:
- Only purchase chicks or layer pullets from M.g.-free farms. This can be checked by having blood samples taken and tested from 24 animals prior to them being moved.
- The standard of operating hygiene must be sufficient to prevent infection being brought in by persons, equipment and other materials. Avoid any direct or indirect contact with infected flocks. We advise very strongly against the reuse of pulp trays. This page provides information on disinfecting, and the GD protocol for ‘Cleaning and disinfecting poultry barns following an M.g. infection’ can also be downloaded here.
- Prevent introduction from the surrounding area. Keep out wild birds by fitting mesh in all openings. Show poultry must also be kept away from the barn. An effective windbreak can considerably limit dust from being blown over from neighbouring poultry farms. This will also provide protection against other pathogens.
At infected layer farms housing multiple age groups, we advise that rearing flocks intended for that farm be vaccinated against M.g. This will render them less susceptible to infection, thus limiting the damage. The hens will however have a positive blood test due to the vaccination. In order to check whether the farm is already free from M.g., a part of a flock (e.g. one percent of the animals) can be left unvaccinated. If those unvaccinated animals remain free from antibodies, it is safe to assume that the farm is no longer infected, and the vaccination process can be stopped.
Prevention is generally better than cure. In combating M.g., the emphasis therefore lies on preventing infection. After all, treatment will only result in (temporary) suppression of the infection, while the treatment options for layers are also extremely limited due to the residue that then occurs in eggs. Treatment is therefore only advised if the problems give serious cause, such as a production drop or respiratory problems. In those cases, we advise you to consult with your veterinarian or GD.
Vaccination using a dead vaccine to combat M.g. will reduce the economic damage in case of infection with M.g. It is a fact that layers can still become infected even after being M.g. vaccinated. Research also shows that vaccination reduces the level of excretion of the M.g. bacteria within a flock.
The current approach to M.g. is based on detecting poultry farms infected with M.g., premature slaughter at infected breeding farms (reducing transmission from maternal parent stock to offspring), optimisation of farm hygiene (reducing transmission from the surrounding area) and vaccination (applied in the layer sector). The current use of M.g. vaccination in the layer sector is mainly intended to contribute to reducing the economic damage caused by M.g. infections in layer flocks and reducing the risk of infection. Vaccination will reduce respiratory problems, losses, egg production drops and transmission of the bacteria from maternal parent stock to their offspring.
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Approach to and prevention of Mycoplasma synoviae (M.s.)
A flock infected with M.s. will remain infected throughout its life. Treatment with antibiotics can only serve to combat any secondary infections. The problems often re-occur once treatment is ceased. Mycoplasma is resistant to antibiotics that lyse the cell wall, such as penicillin, but it is sensitive to quinolones, macrolides and tetracyclines. M.s. is mainly combated by preventing vertical and horizontal transmission. There is very limited use of vaccination worldwide. The discovery that M.s. currently plays a role in arthritis and joint amyloidosis has resulted in renewed interest in M.s. research. M.s. can be transmitted from infected maternal parent stock to offspring via the egg (vertical transmission). Furthermore, this bacteria can infect your chickens via contact between the animals, via introduction from outside, via visitors, via infected materials, etc. (horizontal transmission). M.s. monitoring in 2013 showed that the horizontal transmission of M.s. is most relevant within the Dutch poultry farming sector. These monitoring results (see Table 1 in the flyer) show the M.s. prevalence in the layer sector to be 70% in 2013, even though only 19% of the layer pullet farms tested M.s. serologically positive. This means that flocks subsequently become infected with M.s. (during transport, upon arrival and during the production period, etc.). This also means that any measures that can prevent such introduction/horizontal transmission of M.s. are extremely important.
With this in mind, it is also important to emphasise that a multiple age group system will perpetuate an M.s. infection, due to an infected M.s. flock in situ repeatedly infecting the subsequent flock. In this situation, it is important to continuously pay attention to management measures intended to prevent introduction of M.s. to other farms.
At the request of the PPE advisory committee for poultry healthcare, GD has provided poultry farmers with an information booklet. The information booklet is intended to (1) help you prevent further spread of M.s. from your farm within the poultry sector and (2) to advise you on prevention of reinfections and/or new infections. We also provide you with background information on M.s., with emphasis on the transmission routes.
Legislation for mycoplasma
The monitoring of M.g. at layer farms and farms housing meat turkeys is established at the national level in the Rules for animal husbandry, whereby end layer flocks and meat turkey flocks are tested for the presence of M.g. antibodies prior to slaughter.
Monitoring and prevention of M.g. in breeding animals is covered by EU legislation (Animal Health Regulation, EU 2019/2035). Based on this legislation, the offspring of M.g. and/or M.m. infected breeding stock (chickens and turkeys) may not be sold within Europe.
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