Mycoplasma synoviae (MS) is a bacterial pathogen that commonly affects poultry, particularly chickens and turkeys. This microorganism is unique because, unlike many other bacteria, it lacks a cell wall. This structural difference impacts how the bacterium interacts with its host and influences the effectiveness of certain treatments. MS is found globally and can lead to various health issues in poultry flocks.
Clinical Signs and Forms of Infection
Mycoplasma synoviae infection can manifest in two primary forms, affecting different systems within the bird’s body. The first is the synovial form, also known as infectious synovitis. Birds with this condition often display lameness, a stiff gait, and a tendency to sit frequently. Swelling typically appears in the hocks and footpads, and sometimes breast blisters can develop from prolonged sitting.
Other signs include pale combs, ruffled feathers, depression, reduced appetite, or greenish droppings.
The second common presentation is a respiratory form, which often remains subclinical, meaning birds carry the infection without showing obvious signs of illness. While mild respiratory sounds like rales may occur, more pronounced respiratory disease, such as inflammation of the air sacs (airsacculitis), often develops when MS is present alongside other respiratory pathogens like Newcastle disease or infectious bronchitis viruses. Subclinical infections are particularly challenging because infected birds can spread the bacterium widely without appearing sick, making their detection difficult for flock owners. Mortality rates from MS are generally low, typically ranging from 1% to 10%.
Transmission and Spread
Mycoplasma synoviae can spread through a flock and between different flocks via two main pathways. One method is vertical transmission, where the bacterium passes from an infected hen directly to her offspring through the egg. Although not every egg from an infected hen will transmit the infection, this route plays a significant role in widespread dissemination.
The other common mode of spread is horizontal transmission, which involves bird-to-bird contact. This occurs through respiratory aerosols, such as sneezes or coughs, and direct physical interaction between birds. Contaminated environments also contribute to horizontal spread; equipment, feed, water, and even people or vehicles can carry the bacterium between birds or farms. The introduction of even a single subclinically infected bird can lead to rapid transmission within a flock, with nearly all birds potentially becoming infected over time, regardless of whether they display symptoms.
Diagnosis and Treatment
Diagnosing Mycoplasma synoviae infection typically involves laboratory testing performed by a veterinarian. Serological tests, such as ELISA (Enzyme-Linked Immunosorbent Assay) or serum plate agglutination, are used to detect antibodies in blood samples, indicating exposure to the bacterium. However, these tests may produce false positives or require several weeks post-infection for antibodies to become detectable.
For a more direct and often quicker diagnosis, Polymerase Chain Reaction (PCR) tests are employed to detect the bacterium’s genetic material directly from tissue samples, such as those from the respiratory tract or affected joints. PCR is increasingly favored for its speed and accuracy in confirming the presence of MS. Regarding treatment, certain antibiotics can help manage the clinical signs of an MS infection. Common choices include tetracyclines (like oxytetracycline and chlortetracycline), macrolides (such as tylosin and tilmicosin), and pleuromutilins (like tiamulin).
It is important to understand that while these antibiotics can reduce the severity of symptoms, they often do not eliminate the bacterium from the bird’s system. Infected birds frequently remain carriers for life, capable of intermittently shedding the bacterium and potentially infecting others.
A veterinarian must be consulted for proper diagnosis and prescription of antibiotics to ensure appropriate treatment and to help prevent the development of antibiotic resistance. Providing supportive care, such as maintaining good water hygiene, also contributes to managing the flock’s health during an outbreak.
Prevention and Flock Management
Preventing Mycoplasma synoviae in poultry flocks relies heavily on robust biosecurity measures. Sourcing new birds or chicks from Mycoplasma-free flocks is a primary step to avoid introducing the bacterium. Ideally, this involves purchasing from suppliers participating in programs like the National Poultry Improvement Plan (NPIP), which certifies flocks as free from specific poultry diseases, including MS.
Implementing strict biosecurity protocols for existing flocks is also paramount. This includes quarantining any new birds for a period, typically around 30 days, before integrating them with the main flock. Using dedicated clothing and footwear solely for the coop area helps prevent accidental transmission from outside sources.
Limiting contact with wild birds and rodents, which can carry and introduce the bacterium, further protects the flock. For larger operations, an “all-in, all-out” management system, where an entire group of birds is raised and then removed before a new group is introduced, helps break disease cycles. Vaccines are also available as part of a comprehensive prevention strategy, particularly for larger commercial operations, and can help reduce clinical symptoms and bacterial shedding.