Mycoplasma gallisepticum

The disease was first described in 1905. It was described as a respiratory disease that was found in domestic poultry. However, it wasn't for another 50 years that the causative agent, Mycoplasma gallisepticum, was cultivated. In January 1994, the first house finches with symptoms of M. gallisepticum were observed in the Washington DC area, including part of Maryland and Virginia. In the winter of 1994, an epidemic of mycoplasmal conjunctivitis caused by M. gallisepticum began in house finches. For a time, the disease appeared to be stopped by the Rocky Mountains, After crossing the Rockies, the disease spread south along the west coast before turning back inland. Research using RFID tags to track a sample of wild finches found an individual bird's likelihood of acquiring or transmitting the infection to be positively correlated with time spent at feeders. ==Clinical signs==

House finches Mycoplasma gallisepticum infection in house finches (Haemorhous mexicanus) causes conjunctivitis with the symptoms of periocular swelling, swollen eyelids, ocular and nasal discharge, impaired vision, depression, and weight loss. Infected birds may be listless or seem disoriented, present with reckless or limited flight, and a timid reluctance to flee predators or humans. These symptoms cause house finch populations to decline due to increased predation and susceptibility to trauma from impaired vision, Swollen eyelids, ocular discharge, and loss of sight are signs and symptoms that are very important for this disease as well. M. gallisepticum infections in chickens result in relatively mild catarrhal sinusitis, tracheitis, and airsacculitis." Other avian species Other avian species that have been affected by this disease are pigeons, chukar partridges, quail, ducks, geese, pheasants, psittacine birds, and peafowl. Most songbirds are resistant except for the wild house finches and some similar species in North America. ==Transmission==

M. gallisepticum can be transmitted within some poultry eggs, which can come from infected breeders to progeny. Also, M. gallisepticum can be transmitted via infectious aerosols and through contamination of feed, water, and environment as well as human activity on fomites which can come from equipment and shoes. When birds are stressed transmission can occur more rapidly through aerosols and respiratory which spread through the flock. When they are in a flock, transmission occurs by direct and indirect contact from the movement of the birds, people and fomites from infected species. With many outbreaks, the source of the infection in the flock is unknown. Some sources that could possibly cause infection and transmission are cold weather, poor air quality, concurrent infections, and some live virus vaccinations. ==Diagnosis==

The greatest success in isolating M. gallisepticum has been from tissue swabs from live trapped or newly dead birds. In recent studies, it has been found that generally results obtained from dead birds are more reliable. It is difficult to obtain a sample from frozen carcasses. Tissue swabs are taken from the inner eyelids, sinus, and trachea. Many serology tests can be performed to diagnose M. gallisepticum: serum plate agglutination (SPA) test, hemagglutination inhibition test (HI), or enzyme-linked immunosorbent assay (ELISA). The SPA test is more commonly used because it is the simplest and least expensive. Tests can be performed on serum samples as well as tissue samples. However, it has been stated that serological tests cannot be interpreted without the results to be obtained from the PCR method. It has been found that antibody responses change in the early and advanced stages of the disease and the results vary according to the test method. ==Health concerns==

Mycoplasma gallisepticum causes respiratory disease and weakens the immune system which makes the bird vulnerable to any disease that they come into contact with. Small bubbles will appear in the corners of the eyes and sinuses will swell up. Once infected, they are carriers for the disease for life. Some birds have good resistance to the disease while others may die; some become ill and recover and others may not show any symptoms at all. There is currently no risk to humans. For domestic animals, there is a high concern and there should be a prevention of any interaction between wild birds and domestic poultry. Wild bird species affected by the disease are infectious and are often found in close contact with domestic species. ==Wildlife rehabilitation and treatment==

Wildlife rehabilitators should be careful to not misdiagnose M. gallisepticum infection with other diseases with similar clinical signs, such as avian influenza, chlamydiosis, Newcastle disease, infectious bronchitis, head trauma, and avian pox virus. M. gallisepticum can be treated with antibiotics such as tylosin, tetracycline, or oral enrofloxacin with ophthalmic gentamicin. These are given through food, water or injections. Especially tylosin gives good results in the feed. However, treated birds must be kept in captivity and isolation for a long time period because birds may become asymptomatic carriers. At this point, it is very difficult to verify if previously infected birds are still infected with M. gallisepticum. Treatment and release is not wise for disease control in wild populations. ==Economic impact==

Mycoplasma gallisepticum is believed to cost the worldwide poultry industry over $780 million every year. In the United States it is believed to cost over $120 million on egg production alone. ==References==