Zoonotic diseases of poultry

Poultry is a significant pathogen reservoir. A wide range of zoonotic disease concerns exists in poultry. Disease transmission can occur through infected poultry. A consumer demand is for safe and high-quality animal protein. Backyard and small-scale production flocks are becoming more popular, as is public concern about global chicken disease outbreaks. Humans can contract infections from chickens in two ways. One is transmitted by contact with live birds, while the other is transmitted through food, as a result of exposure to or consumption of infected birds meat or egg products.

Avian influenza

Avian influenza is at the top of the zoonotic list due to its severe zoonotic global events. Avian influenza viruses (AIV) are members of the family Orthomyxoviridae. They are divided into A, B, or C influenzas. The Type A category includes  most of the human influenzas and is also the only one seen in most domestic animals, including birds. All influenza A viruses have two prominent glycoproteins – hemagglutinin (H) and neuraminidase (N). There are 17 different forms of hemagglutinin protein and 7 of neuraminidase. As a result, all influenza A viruses are classified based on which kind of H and which type of N they contain, resulting in the H#N# subtype classification. Birds, unlike other animals, can be infected with all possible H and N combinations, resulting in a total of 153 influenza A subtypes. Because the majority of these viruses do not cause sickness in birds, they are referred to as “low pathogenic avian influenza” (LPAI) strains.

Waterfowl, in particular, are known to facilitate the reproduction of a variety of avian influenza viruses in their intestines, which then spread when they fly and defecate in the air. Some of these “low pathogenic influenza” viruses can infect fowl below, and they have been found to mutate to become virulent within poultry, transforming a “low pathogenic avian influenza virus” (LPAI) into a “highly pathogenic avian influenza virus” (HPAI) that causes sickness. All of these extremely pathogenic viruses so far have been H5 or H7 subtypes. As a result, all H5 or H7 viruses found in birds are deemed “notifiable” due to the risk of them mutating and becoming severe enough to kill poultry.

Humans have been infected by avian influenza virus H5N1 and other subtypes also (H7 and H9). The H9 subtype, has occasionally infected humans with some respiratory impairment, but no deaths. These viruses were of the LPAI variety.

Newcastle Disease Virus

Newcastle disease (ND) is another very deadly poultry disease that causes concern among poultry owners and authorities around the world. This disease, like its cousin, avian influenza, has a zoonotic potential, but it is far less severe in humans.

Newcastle Disease Virus (NDV) is one of the members of the Paramyxoviridae family which infects both poultry and wild birds. NDV has been categorized into five pathotypes based on clinical signs in infected chickens, as viscerotropic velogenic, neurotropic velogenic, mesogenic, lentogenic or respiratory and asymptomatic.

Accidental exposure to vaccines or fluids from infected birds or carcasses is the most common cause of clinical infections in humans. Conjunctivitis usually appears within 24 hours and is accompanied by lacrimation, palpebral edoema, discomfort, and, less commonly, fever, chills, a loss of appetite, and photophobia.

Avian tuberculosis

Infections caused by Mycobacterium avium can be found in a wide range of birds, from poultry and game birds to wild and zoological species, all across the world. In poultry, avian tuberculosis is caused by M. avium serovars 1, 2, and 3. The bacteria first form yellow to white tubercles in the small intestine of birds, then spread to other organs, including the liver, spleen, and bone marrow. The granulomatous disease that results causes emaciation and ultimately death. When diseased birds contaminate the environment by shedding tubercle bacilli, the durable acid-fast bacilli are disseminated via the fecal-oral route.

Infection with M. avium from birds in humans is exceedingly rare in immunocompetent people and more common in immunocompromised people, such as AIDS/HIV patients. Serovar 2, the most prevalent isolate in poultry, is not seen in the majority of serovars isolated in humans.

Avian chlamydosis

Infections caused by Chlamydophila psittaci can be found in over 400 different bird species, often undetected. Only turkeys have a well-defined clinical disease condition, which manifests as a mild respiratory infection in poultry. Because there are numerous genotypes of C. psittaci that tend to infect just certain species, and these species-specific genotypes differ in their severity for birds and people, the disease may be undetectable in other poultry species.

Humans have been infected by turkeys on multiple occasions, as per reports. Inhalation of contaminated aerosols causes infection in either turkeys or people. Infected birds will shed the organism in respiratory and ocular secretions, as well as faeces, whether they are clinically unwell or asymptomatic. When environmental conditions allow, the organism survives drying and becomes aerosolized. Once inside a human, the organisms attack respiratory epithelial cells and subsequently enter macrophages, where they can spread throughout the body and cause widespread necrotizing and inflammatory lesions in visceral organs like the liver.


Salmonella is a zoonotic pathogen that causes gastrointestinal sickness in both humans and animals. One of the most common sources of human Salmonella infections is poultry items contaminated with these pathogens. Salmonella typhimurium and Salmonella Heidelberg can infect chickens and transfer to other hosts, including humans, without causing illness. When materials from the digestive tract contaminate carcasses at slaughter, problems arise. Inadequate hygiene measures in the home during food preparation will therefore result in disease transfer to humans.

Salmonella enteritidis can infect the female reproductive system of chickens, causing the hen to exhibit no clinical indications, but the bacterium will be excreted into the eggs, causing sickness in people. Cooking eggs thoroughly kills the organism. Uncooked egg products in food, such as caesar salad dressing or egg nog, can cause human sickness. The organism on entering the intestinal tract stimulates a secretory diarrhea and also destroys epithelium, creating ulcers and an effusive diarrhea. The endotoxin on Salmonella leads in cytokine activation and massive cytokine release known as septic shock.


Campylobacteriosis is the most common foodborne gastroenteritis disease, and it is a major public health concern in developed countries. Campylobacter jejuni, a zoonotic pathogen, is the leading cause of disease in humans. Within 2 to 5 days of ingesting the organism, people develop sporadic gastroenteritis, which causes abdominal discomfort, watery to bloody diarrhoea, and an occasional fever that can last anywhere from a day to a week. Following infection, death (typically in immunocompromised people) or serious sequelae such Guillain-Barré syndrome, reactive arthritis, nephritis, myocarditis, pancreatitis, or septic abortion can ensue. During processing, one infected carcass can easily contaminate the entire production line and thus, much of the control measures in place focus on this stage of production.

Escherichia coli 

E.coli is naturally present in the gastrointestinal tract of animals and people. Avian colibacillosis is a disease that affects chickens, turkeys, and ducks. It is caused by opportunistic virulent strains, the majority of which are extraintestinal E.coli. It can be localised or systemic. Poor management, poor sanitation, or a secondary infection following respiratory or immunosuppressive disease are all common causes of disease. It is a major economic concern around the world.

Some types of E. coli are harmful and can cause disease especially in people with compromised immune systems. E. coli infections can result from accidental ingestion of fecal material or consumption of contaminated, undercooked foods. Infected birds usually do not show any signs, but people infected with harmful E. coli can have severe symptoms such as bloody diarrhea and even kidney failure.


Although human infections are infrequent, there are significant zoonotic dangers associated with chicken and poultry products that veterinarians and general public should be aware of and consider in their everyday practise.

Asiya Mushtaq

PhD Scholar, Department of Veterinary Microbiology, GADVASU