Prevention and Treatment Methods for Mycoplasma gallisepticum Infection

I. Disease Overview;

Mycoplasma gallisepticum infection mainly manifests in chickens as respiratory symptoms, such as tracheitis, airsacculitis, etc., so it was once named chronic respiratory disease. In turkeys, aside from airsacculitis, it mainly causes infectious sinusitis. This infection is distributed worldwide and is also very common domestically.

Mycoplasma gallisepticum has the general morphological characteristics of mycoplasmas, is Gram-negative, ferments glucose, does not hydrolyze arginine, does not obtain energy from urea, is sensitive to digitonin, reduces tetrazolium, adsorbs chicken red blood cells, lyses sheep red blood cells, and does not form films or spots. Mycoplasma gallisepticum has the ability to move slowly, and this ability may be related to a special ultrastructure, namely a vesicle-like structure at one end of the cell, occasionally at both ends; the mycoplasma uses this vesicle to contact eukaryotic cells, and when moving, moves in the direction of the vesicle.

Mycoplasma gallisepticum has weak resistance to the environment. It dies immediately in water. It can survive 1-3 days in chicken manure at 20 degrees. In egg yolk at 37 degrees it survives 18 weeks, and at 45 degrees it dies after 12-14 h. Liquid culture kept at 4 degrees does not exceed 1 month, at -30 degrees it can be preserved for 1-2 years, and at -60 degrees it survives even longer.

II. Epidemiological Characteristics;

Mycoplasma gallisepticum infection is prevalent in chicken farms worldwide. According to serological surveys, the average infection rate is between 79%-80%. Factors affecting the prevalence of Mycoplasma gallisepticum infection, aside from the pathogenicity of the mycoplasma itself, clearly include the age of the chicken; the susceptibility of chickens to mycoplasma infection strengthens with increasing age. Concurrent infection has a considerable impact on Mycoplasma gallisepticum infection; even a recessive infection with weakly pathogenic Mycoplasma gallisepticum often results in an outbreak of clinical mycoplasma disease after vaccination with Newcastle disease vaccine or infectious bronchitis vaccine.

Environmental factors also play an important role affecting the prevalence of Mycoplasma gallisepticum infection. Overcrowding of the flock intensifies the spread of the pathogen, and at the same time overcrowding is a stress that reduces the chickens' resistance. Dirty chicken houses, accumulated manure, and increased ammonia content in the air irritate the respiratory mucosa, facilitating the development of mycoplasma.

Nutritional deficiency can lead to the occurrence of mycoplasma disease. The spread of mycoplasma mainly occurs in two ways. One is direct contact, in which droplets carrying mycoplasma exhaled by infected poultry are transmitted through the respiratory tract to chickens or turkeys in the same house or cage. The other way is transovarian transmission, in which the pathogen is transmitted through the eggs of infected chickens to the next generation; this way may be more important. In some regions, especially developing countries, ordinary eggs are often used for chicken embryo culture to manufacture live vaccines for poultry; mycoplasma transmitted through eggs develops in chicken embryos and contaminates the vaccine, and through vaccination it infects the vaccinated chickens; the role of such contaminated vaccine in transmission cannot be ignored.

III. Clinical Symptoms:

The most common symptoms of infection are respiratory symptoms, manifested as coughing, sneezing, tracheal rales and rhinitis. Rhinitis is especially common in turkeys; the affected poultry has inflammation and swelling of one or both infraorbital sinuses, and in severe cases the eyes cannot open. Often nasal discharge plugs the nostrils, and sometimes the nostrils are completely filled with a mucous mixture; the sick poultry frequently shakes its head, eager to shake it off, and sometimes wipes its nose with its wings so that the wings become soiled with nasal discharge. Mild conjunctivitis often occurs, with clear ocular discharge, but sometimes the eye inflammation is also very severe. Sometimes joint inflammation occurs, causing lameness, but inability to stand is rarely seen. The production performance of infected flocks declines.

IV. Differential Diagnosis:

Because the external symptoms of Mycoplasma gallisepticum disease are not specific, when respiratory symptoms appear in a flock, attention should be paid to differential diagnosis from Newcastle disease, infectious bronchitis, infectious rhinitis, Mycoplasma synoviae infection and fowl cholera; when sinusitis appears in turkeys, attention should be paid to differential diagnosis from chlamydial infection. For differential diagnosis, some cases can use serological methods, and some can use pathogen isolation methods.

V. Prevention and Treatment Measures:

Prevention:

At present, our country has not yet bred mycoplasma-free breeding chicken flocks; it can be said that Mycoplasma gallisepticum infection exists in all chicken farms, and under normal conditions no obvious symptoms appear. Once stressed by unfavorable factors, disease may break out and cause death. Therefore, routine feeding management must be done well, balanced feed provided, attention paid to cleanliness and hygiene, no accumulation of manure or urine in the house, no overcrowding in cages, and avoidance of various

stress factors:

1. Vaccination Vaccination is an effective method to reduce mycoplasma infection. There are two types of vaccines, attenuated live vaccines and inactivated vaccines.

Attenuated live vaccine: At present, the live vaccine used internationally and domestically is the F strain vaccine. The F strain has extremely slight pathogenicity; eye-drop vaccination of 1-day-old, 3-day-old and 20-day-old chicks does not cause any visible symptoms or air sac changes and does not affect weight gain. When vaccinated simultaneously with Newcastle disease live vaccine B1 or LaSota strain, it neither enhances each other's pathogenicity nor affects each other's immune effect. The immune protection rate is above 85%, and immunity lasts at least 7 months.

Inactivated vaccine: Oil-adjuvant inactivated vaccine has good effects; after use it can prevent the occurrence of this disease and reduce the induction of other diseases, and increase egg production. There are reports abroad that chickens used for two consecutive generations can clear mycoplasma infection within the flock.

2. Clearing Mycoplasma gallisepticum in breeding eggs Transovarian transmission is an important transmission route of Mycoplasma gallisepticum; blocking this route is of great significance for preventing and treating the disease and is the basis for breeding mycoplasma-free chickens. Two methods can be used to reduce or eliminate mycoplasma in eggs: antibiotic treatment and heating method.

Antibiotic treatment: Warm the breeding eggs before incubation to 37 degrees and then immediately place them in an antibiotic solution at about 5 degrees that has an inhibitory effect on mycoplasma for 15-20 minutes; the eggs can also be placed in an antibiotic solution in a sealed container, part of the air withdrawn, and then air slowly let back in so that the medicinal liquid enters the eggs; there is also the method of injecting antibiotic solution into the eggs.

Heating method: For breeding eggs in the incubator, hot air is forced in so that the temperature rises uniformly to 41.6 degrees within 12-14 h, and then they are moved to normal incubation temperature for incubation; this can achieve relatively satisfactory results in eliminating mycoplasma in eggs. However, the hatchability of breeding eggs decreases by 8%-12%.

3. Breeding mycoplasma-free infected flocks.

Treatment:

At the early stage of disease, some antibiotics with an inhibitory effect on mycoplasma can be tried for treatment. Antibiotics can be mixed into feed or administered through drinking water, or injected. The dosage of oxytetracycline and tetracycline is 400 g per ton of feed; tylosin is 2-3 g added to every 4.5 L of water; kitasamycin is 300-500 g per ton of feed. The drinking water content of tiamulin (Mycoplasma Clear is a preparation of tiamulin) is 120-500 mg/L; whether administered in drinking water or mixed into feed, it must be used for several consecutive days. If the medication effect is poor, then the problem of concurrent disease should be considered, or the relationship of the pathogen strain having resistance to the antibiotic used.