**7.3 History and transmission**

Firstly reported cases of the isolates have reported the susceptibility of bones with this pathogen and the prominent clinical signs as synovitis and arthritis [63–66]. Navel of the day-old chicks, surgery as trimming, and vaccination in un-hygienic conditions can be the trigger for the infection. Diseases that involve the predilection site to be the immune organs as being directly involved can also the root cause of this infection as the infectious bursal disease [67] and chicken infectious anemia. This is usually fatal as it leads to septicemia. Aged turkeys can have this infection with exposure to the hemorrhagic enteritis virus (HEV) [68]. Genetics of the poultry as the major MHC is also the predisposing factor for the skeletal-related problems of the poultry [69]. The incubation period of 2–3 days is a thumb rule but it is dependent upon several factors as the immune status of the host, the potency, and route of infection of the bacteria as the aerosol and tracheal routes are reported not to be the potent routes of infection [70, 71]. Infections with less than 105 organisms/kg body weight are reported to be defeated by the immune system of a healthy bird [25, 72].

### **7.4 Clinical signs, morbidity, incubation period, and pathology**

Clinical signs of this disease include lameness, depression, pyrexia, and gait abnormalities, and death. Survived animals have arthritis, osteomyelitis [73, 74] unable to stand and sit on the hock and keel [25, 75]. This makes the fragility of the bones, mostly the femur and the tibiotarsus. It also leads to the congestion of the spleen, liver, lungs, and kidneys [23], gangrenous dermatitis, and ultimately the "blue wing disease" that presents the infection to the tip of wings of the birds that are infected with the chicken infectious anemia virus. Other clinical signs include enlarged yolk sac, planter abscess, discolored liver [27, 76]. Usually, the bacteria are not subjected to enough titer that may be the cause of higher mortality rates as compared to another fatal disease as the New Castle disease, etc., under optimal environmental conditions with most of the birds. But this bacterium has also been reported to have very high mortality rates that were primarily due to the immunecompromised state of the birds and the poor management conditions, and this bacteria in these conditions too is not the primary cause of the losses. The common site for the isolation and identification of that agent is the joints [18, 76–78].

#### **7.5 Immune response**

There are no convincing reports of the facts the active immunity or passive immunity other than that of the anti-*Staphylococcus aureus* antibodies may have any effect on this bacterium [79, 80]. Immunized hens can have antibodies within their

egg yolk that can be used to prevent the bacteria in vitro. Toxoids are ineffective in other species [81, 82], and vaccines have not proven to be a very effective way of controlling the disease [83–86].
