Chicken colibacillosis is a general term for different types of diseases in chickens caused by certain pathogenic serotypes of Escherichia coli.
It is characterized by pericarditis, perihepatitis, airsacculitis, peritonitis, ocular inflammation, arthritis and synovitis, salpingitis, Escherichia coli enteritis, granulomas, septicemia, and other conditions in chickens. The disease was first reported in Sweden and subsequently occurred in many countries around the world.
Since the nineteen eighties, the disease has continued to spread and expand in China. In recent years in particular, Escherichia coli disease has been widespread at many poultry farms, with persistently high morbidity and mortality rates. In addition, Escherichia coli readily develops drug resistance, driving up treatment costs. This poses a serious threat to the healthy development of the poultry industry and causes it huge economic losses.
Cause of onset
I. Incorrect use of antibacterial drugs
Users often regard medication as the primary means of controlling Escherichia coli. However, antimicrobial susceptibility testing is not widely used, and medication is often administered without sufficient guidance. In actual production, medication is sometimes used inappropriately, such as arbitrarily increasing the dosage, using low doses for a long time, administering drugs by an inappropriate route, or failing to rotate medications. This can lead to Escherichia coli developing drug resistance, reducing the effectiveness of the drugs or even rendering them ineffective, and making drug-based control more difficult. In addition, drug abuse can disrupt the microbial flora in the body, which is also a common predisposing factor for colibacillosis.
II. Effects of immunosuppressive diseases
In our country, infections with immunosuppressive diseases in poultry are very widespread. These diseases can damage the body’s entire defense system, including humoral immunity, cellular immunity, nonspecific immunity, and local immunity, resulting in immunosuppression or reduced immune function and increasing susceptibility to Escherichia coli.
III. The level of purification in the breeder flock is low
Immunosuppressive diseases caused by chicken infectious anemia virus (CIAV), subgroup J avian leukosis virus (ALV-J), reticuloendotheliosis virus (REV), and reovirus are transmitted vertically to chicks through hatching eggs.
Four. Infectious bursal disease virus
Four. Infection with infectious bursal disease virus (IBDV) or use of a relatively virulent infectious bursal disease vaccine causes bursal damage, a reduction in lymphocytes, and impaired differentiation and maturation, leading to immunosuppression.
Six. Immunosuppression
Six. In China, broiler flocks other than those of Sanhuang chickens do not use Marek’s disease vaccines, leaving most broiler flocks in China susceptible to immunosuppression caused by infection with virulent Marek’s disease virus.
Seven, numerous serotypes
Seven. There are numerous serotypes, and different regions have different predominant serogroups. The antigenic structure of Escherichia coli is complex, consisting of three parts: somatic antigens, capsular antigens, and flagellar antigens. Many antigens are currently known, and these can combine to form numerous serotypes with different antigenic properties. As a result, different regions within the country each have their own predominant serogroups, and serotypes can vary considerably between farms in the same region. Multiple serotypes may even be present within the same flock at the same chicken farm.
Because antigenic cross-protection between different serotypes is weak, it is impossible to produce a super-broad-spectrum vaccine that covers all serotypes. Moreover, Escherichia coli is not highly immunogenic. Therefore, even when the bacterin is of good quality, the actual immunization results in production are not very satisfactory with an inactivated bacterin corresponding to the serotype.
Eight. Vertical transmission of Escherichia coli
There are two routes of vertical transmission: one is infection of the hen’s ovaries and oviducts associated with septicemia and peritonitis caused by Escherichia coli, resulting in contamination inside the egg and transmission to the next generation of chicks; the other occurs when hatching eggs are initially free of bacteria, but their shells are contaminated with Escherichia coli in feces. The bacteria can penetrate the eggs during storage or incubation, causing embryonic death, egg explosions, or infection in chicks after hatching. In this case, infection can be more severe if disinfection during incubation and hatching is inadequate.
Nine. Mycoplasma infection
In particular, Mycoplasma gallisepticum infection acts synergistically with Escherichia coli in causing disease and is also one of the common triggers of colibacillosis. In addition to horizontal transmission, mycoplasma can be transmitted vertically through hatching eggs to chicks when the breeder flock has a low level of mycoplasma control. Infection can also result from using live vaccines manufactured with non-chicken embryos containing mycoplasma. These are also transmission routes that should not be overlooked.
Ten. Secondary infection
Secondary infections are mainly caused by infection with Newcastle disease virus, avian influenza virus, and infectious bronchitis virus in chickens. Some highly pathogenic strains are often easy to diagnose because they can cause death, but those that are not highly pathogenic are often difficult to detect and distinguish. It is precisely these non-highly pathogenic strains, which remain widespread in poultry environments, that often damage the integrity of the mucosal barrier systems of the respiratory and digestive tracts, causing infected poultry to experience varying degrees of immunosuppression and thereby opening the door to invasion by Escherichia coli.
Eleven, poor husbandry and management, severe environmental pollution, and persistent stressors
Chicken colibacillosis is a conditional disease. Poor environmental conditions and various stress factors can promote its occurrence and spread. These factors include sudden climate changes, cold, heat and humidity, inadequate ventilation, and excessive ammonia odors. They weaken the flock’s resistance to disease, allowing various pathogens to invade and cause illness.
Poor sanitary conditions and the failure to safely dispose of feces, wastewater, and dead chickens have led to severe environmental pollution at the poultry farm, with large numbers of bacteria and viruses present. A lack of attention to disinfection or lax disinfection practices, excessive stocking density, and a damp environment have also created conditions for the proliferation of E. coli and other pathogenic microorganisms.
Twelve. Other reasons
Nutritional deficiencies in feed, insufficient vitamin content, feed mold, and other factors can reduce chickens’ resistance and increase their susceptibility to E. coli, leading to the occurrence of colibacillosis.