Bacterial diseases are the most common in livestock and poultry farming. Although we cannot see or touch bacteria, since the invention of the microscope, people have been able to observe them firsthand in the microscopic world. So when Escherichia coli, Salmonella, Pasteurella, Avibacterium rhinotracheale, and others are mentioned today, no one doubts their existence.
Among these pathogens, Gram-negative bacteria, Gram-positive bacteria, and mycoplasmas receive considerable attention. Anaerobic bacteria such as Clostridium, although also widespread in nature, are often overlooked. However, the harm they cause should not be underestimated. Under normal circumstances, anaerobic bacteria live in oxygen-free environments, aerobic bacteria need oxygen to live, and facultative bacteria can live in either oxygenated or oxygen-free environments.
In poultry farming, bacteria are present in most parts of a chicken’s body and throughout the poultry house. Chickens take in bacteria every time they breathe, eat, or drink. When the number of pathogens ingested is great enough to overcome the body’s own defenses, or when the body’s resistance to disease falls below a certain threshold, bacteria can cause disease in chickens. Of course, some bacteria can cause disease even in very small numbers.
As pathogens requiring special conditions to live, anaerobic bacteria are present on all parts of the body surface, and even in the lungs and intestines, in astonishing numbers. Under normal circumstances, anaerobic bacteria and other bacteria remain in balance, and no problems arise. Once this balance is disrupted and environmental conditions meet the needs of anaerobic bacteria for growth, they multiply rapidly and cause disease. Infections caused by anaerobic bacteria are mostly endogenous, meaning they are caused by bacteria already present in the body.
Conditions that trigger the proliferation of endogenous anaerobic bacteria and cause disease include immunosuppression, trauma, inadequate blood supply, necrosis, cachexia, and the growth of aerobic or facultative bacteria (which creates an oxygen-free environment).
Of the various anaerobic bacteria found in poultry, the most important group is Clostridium. Clostridium is found in all poultry houses and in most soils around the world. One of its most important characteristics is its ability to form spores. These spores are very small and highly resistant to adverse conditions; in theory, they can survive for hundreds of years.
Clostridium can also produce the most potent toxins known to date. After these toxins enter a chicken’s body, they damage and kill the tissues they come into contact with, destroy red blood cells and thereby reduce the blood’s oxygen-carrying capacity, and sometimes prevent nerve impulses from being transmitted to the heart and lungs.
In recent years, clostridial diseases in poultry have occurred sporadically in various regions, seriously affecting poultry farmers. These diseases mainly include ulcerative enteritis caused by Clostridium colinum, necrotic enteritis caused by Clostridium perfringens, and gangrenous dermatitis caused by Clostridium septicum.
1, Ulcerative Enteritis
Ulcerative enteritis is an acute infectious disease caused by Clostridium colinum and characterized by diarrhea, intestinal ulcers, and sudden, rapid death. It often occurs alongside or after coccidiosis or other stressors that can damage intestinal integrity. The disease also often occurs following immunosuppressive diseases, such as infectious bursal disease or chicken anemia virus infection.
The disease is mainly transmitted when chickens ingest contaminated feces, feed, drinking water, or litter. Chickens that die acutely appear normal externally, have well-fleshed muscles, and have feed in their crops, showing almost no signs of illness. Chronically affected birds show lethargy, ruffled feathers, full crops, abdominal distension, and loose, watery white droppings.
In affected chickens, the intestines are prone to rupture, and deep ulcers appear on the inner surface of the intestinal wall. The ulcers may penetrate the intestinal wall, and ulcerative lesions may be distributed throughout the entire intestinal tract, including the ceca. Chickens affected by coccidiosis, by contrast, are likely to show only general enteritis without ulcerative lesions, with the enteritis lesions relatively confined to one region of the intestinal tract. In birds with ulcerative enteritis caused by clostridia, numerous round yellow to yellow-green areas of discoloration are also commonly seen on the liver.
An essential differential diagnosis is to determine whether the liver lesions are caused by histomoniasis (blackhead disease). Characteristic lesions of histomoniasis are caseous necrosis of the ceca and coin-shaped necrotic lesions in the liver.
2, Necrotic Enteritis
Necrotic enteritis is an acute infectious disease caused by Clostridium perfringens and characterized by bloody droppings and necrosis of the small intestinal mucosa. It often occurs after the ingestion of high levels of fishmeal or wheat, and commonly accompanies or follows coccidiosis. This bacterium rarely causes disease in chickens with an intact intestinal tract unless the intestinal mucosa is damaged.
The disease is transmitted through ingestion of contaminated feces, soil, drinking water, feed, or litter, and has a high mortality rate. Affected birds are extremely lethargic, with reduced or even absent appetite, and pass watery, sauce-colored droppings. Some cases show limb spasms, a twisted head and neck, legs splayed outward, and difficulty breathing; mucus mixed with feed flows from the mouth. Affected birds often lose weight rapidly and die acutely.
On necropsy, lesions in affected birds are confined to the small intestine, especially the jejunum and ileum. The intestines are distended and filled with gas; the intestinal mucosa is thickened and covered with a layer of yellow-green pseudomembrane. The intestinal contents are mixed with blood. In severe cases, the entire jejunum and ileum may be filled with blood. In some cases, mucus is present in the trachea and the larynx is hemorrhagic.
Necrotic enteritis and ulcerative enteritis are easily confused. Ulcerative enteritis causes necrosis and ulcers in the small intestine and ceca, with necrotic foci on the liver surface. Necrotic enteritis, by contrast, affects the jejunum and ileum, while the liver and ceca are rarely affected.
3, Gangrenous dermatitis
Gangrenous dermatitis is caused by a combined infection with one or more pathogens: Clostridium septicum, Clostridium perfringens, and Staphylococcus aureus. In most cases, gangrenous dermatitis is a secondary condition associated with certain diseases. The disease generally occurs in poultry chicks aged 2-3 weeks.
The disease may also occur following ingestion of contaminated feces, feed, drinking water, or litter. Staphylococci are common resident bacteria on the skin and mucous membranes. If an immunosuppressive disease occurs before the integrity of the skin is compromised, the pathogens can enter through a wound and cause this disease.
Affected birds are lethargic, anorexic, weak in the legs, and uncoordinated. The disease course is very short, generally no longer than one day, and acute death often occurs without any symptoms. The skin of affected birds is black; the subcutaneous tissues of the wings, breast, abdomen, and legs show blood-like edema. The muscles are grayish-brown, with edema and gas between the muscle bundles. Most internal organs show no lesions, though scattered white necrotic foci are sometimes visible in the liver.