What factors cause or predispose to respiratory disease in poultry?

What factors cause or predispose to respiratory disease in poultryRespiratory physiology of poultry is unique. Unlike human respiratory anatomy the avian lungs do not expand or contract on breathing. The direction of the flow of gases is unidirectional in the lungs making it more efficient in gas exchange.  The air sacs associated with the poultry respiration form a very important component for air storage during inhalation or exhalation.  The air sacs also regulate body temperature by diverting air flow to pneumatic bones for effective heat exchange.

All etiologies for respiratory disease in poultry have an aerosol mediated entry point. The contact of these agents with the capillary system associated with the lungs is brief as they are diverted to the air sac for temporary storage. Air sacculitis forms a major finding for respiratory related mortalities on post mortem examinations. Keeping these facts in mind we can list factors affecting respiratory disease as;

Environmental stress affecting breathing of the birds

a) Heat/cold stress

b) Handling stress

Immunisation failures

a) Vaccine component failure

b) Immunodeficiency

Inflammatory agents affecting respiratory system

a) Microbial etiology in bio-aerosols

b) Irritant gases and particulates

Nutritional deficiencies

a) Hypovitaminosis ( A & B 12)

b) Amino acid deficiencies

Respiratory Disease In Poultry

Respiratory Disease In PoultryImagine a flock of 1000 chickens or may be a few backyard chickens. In both the case you can encounter major challenge in controlling respiratory diseases, when trying to maintain a healthy flock. So what are the most common signs you see in your flock. These could be- sneezing, discharge around the nostrils and eyes, open mouthed breathing, ruffled feathers, head shaking and wheezy breathing sounds.

The most common causes are described in brief below:

Newcastle Disease (ND), also known as pneumoencephilitis, is highly contagious and that attacks the internal organs (viscerotropic). All birds of wide age groups are susceptible to ND. Humans and other mammals are also affected by ND. ND occurs in three forms, lentogenic (mildly pathogenic), mesogenic (moderately pathogenic) and velogenic (highly pathogenic). It is characterized by a sudden onset of clinical signs including hoarse chirps (in chicks), watery discharge from nostrils, labored breathing (gasping), facial swelling, and paralysis, trembling and twisting of the neck. In laying birds, show symptoms such as decreased feed and water intake and a substantial drop in egg production. Newcastle virus can be transmitted by the air borne route or wild birds, contaminated footwear, workers, visitors, and dirty equipment. Newcastle virus is also transmitted in the egg and the infected embryos die before hatching.

In live birds, the virus is shed in body fluids, secretion, excreta and breath. There is no specific treatment for ND. Antibiotics can be given for 3-5 days to prevent two bacterial infections. However, prevention programs should include good sanitation, vaccination and implementation of a comprehensive biosecurity programme.

Infectious Bronchitis, also known as bronchitis or cold. It is found only in chickens. Similar disease occurs in quail caused by a different virus. The severity of infection is influenced by the age and immune status of the flock, by environmental conditions and by the presence of other diseases. Breathing noises are evident with a watery discharge from the eyes and nostrils. Feed and water consumption declines. Egg production drops dramatically. The IBV infects many tissues of the body, including the reproductive tract. It is known to spread by air, infected dead birds, infected houses and rodent. No specific treatment is available. But it can be prevented by enforcing a bio-security program. Vaccinations are also available.

Infectious coryza mostly affects chickens, pheasants and guinea fowl. It shows swelling around the face, foul smelling, thick, sticky discharge from the nostrils and eyes, labored breathing and rates. The birds may have diarrhea and growing birds may become stunted. Mortality is usually low. Transmission is primarily by direct bird-to-bird contact. This can be from infected birds brought into the flock as well as from birds which recover from the disease. Sulfadimethoxine is the preferred treatment antibiotic. Others such as erythromycin, sulfamethazine, and tetracycline can be used as alternative can be used as alternative treatment. Good management and sanitation are the best ways to avoid infectious coryza.

Avian influenza can occur in most, if not all, species of birds. AI is categorized as mild form which produces loss of appetite, listlessness, diarrhea, respiratory distress, dramatic drops in egg production and low mortality. The highly pathogenic form produces blue comb, facial swelling, wattles and dehydration with respiratory distress. Egg production and hatch ability decreases. There can be an increase in production of soft-shelled and shell-less eggs. AI virus can remain viable for long period of time at moderate temperatures. It can spread through shoes, clothing, crates and other equipment. Insects and rodents may mechanically carry the virus from infected to susceptible poultry. Broad spectrum antibiotics may reduce losses from secondary infections with proper nutrition, good husbandry. A vaccination program used in conjunction with a strict quarantine has been used to control mild form of the disease. With the more lethal form, strict quarantine and rapid destruction of all infected flocks remains the only effective method of stopping an avian influenza outbreak.

Infectious Bursal disease, also known as infectious bursitis mostly affects chickens. In affected chickens greater than three weeks of age, there is usually a rapid onset of the disease with a significant drop in feed and water consumption, watery droppings leading to soiling of feathers around the vent, and vent pecking. The virus is spread easily by infected bird contact, as well as by contact with contaminated people and equipment. The virus is also shed in the bird droppings and can be spread by air through dust particles. Dead birds are good source of the virus which should be incinerated. Antibiotics, sulfonamides and nitro-furans have little or no effect. Vitamin-electrolyte therapy is seldom effective. High levels of tetracycline are contaminated because they tie up calcium, thereby producing rickets. A vaccine is commercially available.

Fowl pox, also known as bird pox, sore head, avian diphtheria, chicken pox (not to be confused with chicken pox in humans). It affects mostly poultry, turkey, quail, duck; chickens- of all ages are susceptible. The clinical signs occur in two forms. The dry form characterised by raised wart-like lesions on un-feathered areas (head, legs, vent, etc). The lesions heal in about two weeks. In laying hens, infection result in a transient decline in egg production. The wet form shows presence of canker-like lesions in the mouth, trachea, pharynx, and larynx. It may cause respiratory distress by obstructing the upper air passages. Mosquitoes are the primary reservoir and spreaders of fowl pox on poultry ranges. Mosquitoes are infected by feeding on birds with fowl pox in their blood stream. Fowl pox can also be transmitted through direct contact with infected to susceptible birds. Currently, no treatment is available; however, fowl pox outbreaks can be controlled by killing mosquitoes. If fowl pox is endemic in the area, vaccination is recommended.

All the above diseases depict the significance of bio-security that is required in the farm. To help maintain a healthy poultry flock, farmers should buy birds from a reliable source, maintain a clean pen, feed an appropriate diet and protect the birds from disease and predators through proper biosecurity. Small flock owners should seek guidance from veterinary doctors if they have queries about the healthy and management of their flocks. In addition to improving animal welfare, economy, occupational health and consumer protection, future-oriented sustainable farm animal production should enhance standards aimed at preventing or reducing the respiratory diseases through air.