The avian infectious bronchitis virus (IBV) population is not constant. Prevention of avian infectious bronchitis (IB) is complicated by the presence of a large number of virus serotypes that differ in antigenicity. The high genetic diversity of IBV in Moldova is explained by the high mutability of the genome and the constant use of live vaccines. It should be noted that new strains do not replace the old ones, which continue to stand out often too. And the old strains, in turn, do not disappear, but simply degenerate "mutate". The primary and main site of virus replication is the tracheal epithelium. From this place, the virus spreads to other organs of the lungs, spleen, liver, kidneys, oviducts, ovaries, testes, digestive and intestinal tracts. In the trachea, kidneys, fabric bag, the virus is detected within 24 hours after infection. The virus can be excreted for a long time from the tonsils of the cecum (up to 14 weeks) and from feces (up to 20 weeks). In IB, three clinical syndromes are noted: respiratory, nephros-nephritis and reproductive. The incubation period for IB depends on the infectious dose and the route of infection and lasts from 18 hours (with infection intratracheally) to 36 hours (intraocularly). The manifestation of clinical signs also depends on the age of the bird, the virulence of the strain of the virus and the current level of immunity. More susceptible chickens up to 2-6 weeks of age. Which manifests a respiratory syndrome characterized by cough, shortness of breath (with an open beak), nasal discharge, tracheal wheezing, sometimes conjunctivitis, rhinitis, sinusitis. The lumens of individual bronchi are completely filled with a dense fibrinous mass. In the cavity of the air sacs, foamy exudate with flakes of fibrin. In small chickens - catarrhal rhinitis and sinusitis. General weakness is observed, followed by depression. Food intake and body weight are significantly reduced, feathers are tousled, wings are lowered.Disease of chickens leads to abnormal development of reproductive organs, and the appearance of "false" laying hens - chickens that can not carry eggs. Clinical signs in uncomplicated infections may not last long, usually less than 7 days. Mature follicles have defects, the yolk seeping through the leak, accumulates in the abdominal cavity, as a result of which vitelline peritonitis may develop. In "false" layers, the lumen of the oviduct is overgrown. They ovulate in the body cavity. Often complicated by a secondary infection of E. coli, colibacteriosis and mycoplasmosis, resulting in increased respiratory symptoms. A chronic respiratory disease develops that can last several weeks with a mortality rate of 5-25%. Mycoplasma leads to more acute clinical signs with growth depression. Reproductive syndrome manifests itself in chickens older than 6 months. Their disease is asymptomatic or with minor damage to the respiratory system. The disease is manifested in the form of a prolonged decrease in egg production. After illness, chickens for a long time lay small eggs of irregular shape with a thin shell. The nephro-nephritic form of chicken infectious bronchitis is characterized by weak and short-term respiratory symptoms, followed by inhibition. The bird is ruffled, bored by heat sources, consumes excessive amounts of water, and quickly loses weight. Characteristic is liquid droppings. Mortality is observed 12 days after infection. In young animals affected by jade, mortality reaches 25%. With nephronephritic kidney syndrome, yellow-brown in color, with a mottled pattern, due to the accumulation of urates in the urinary tubules. Flabby consistency. The ureters are stretched with uric acid salts. General carcass cyanosis, dehydration, and uneven skeletal muscle staining are noted.  Thus, avian infectious bronchitis significantly delays the growth and development of a growing number of poultry, leads to direct economic damage and to a decrease in the quality and safety of food eggs and poultry meat.