INFECTIOUS VIRAL DISEASES OF CHICKEN

Dr. Satuti Sharma (PhD Scholar), Dr. Shilpa Sood (Associate Professor), Dr. Nawab Nashiruddullah (Professor), Dr. Shafiqur Rahman (Assistant Professor), Dr. Sankalp Sharma (PhD Scholar), Dr. Prabjot Singh (MVSc), Division of Veterinary Pathology, F.V.Sc & AH, SKUAST- Jammu, J&K, India (181102).

Introduction

Respiratory infections in chicken are seen worldwide but especially in temperate poultry-producing areas in winter months. There are many common viral diseases which can affect the respiratory system (air passages, lungs, air sacs) of poultry. Dust, ammonia and other gases, and other factors associated with poor ventilation, may act as predisposing factors. Morbidity is typically 10-20%, mortality 5- 10%. If condemned birds are included mortality may be more than 10%.

Ranikhet disease

Ranikhet disease also known as Newcastle disease is highly contagious of chicken caused by paramyxovirus. There are five main forms of the disease: the highly pathogenic viscerotropic velogenic, neurotropic velogenic, mesogenic, mildly pathogenic is lentogenic and lastly is asymptomatic. In case of severely pathogenic form of the disease there is very high morbidity and mortality. Within a span of three or four days most birds on the farm can get the infection. In disease produced by less severe stains of the virus, the birds may remain asymptomatic. However, in birds that survive or those suffering less virulent form of the disease, the case get complicated and the birds become predisposed to develop secondary bacterial infections like Collibacillosis or mycoplasmosis.

Spread:

The disease can spread mechanically by means of contaminated equipment, shoes, clothing and aerosol. Recovered birds are not known to act as carriers. The virus can be transmitted by contaminated equipment, shoes, clothing and free-flying birds.

Clinical Signs:

In virulent forms of the disease, the sick birds exhibit clinical signs reflecting the involvement of respiratory system, nervous system and digestive system. Signs of respiratory system involvement are non specific and include nasal discharge, difficulty in breathing, gasping and sneezing. Birds also show nervous signs which are manifested as paralysis of wings, legs or twisting of the head and neck. Birds may also suffer from diarrhea.

Lesions:

Gross lesions are seen in the digestive tract or respiratory tract. Varying amounts of mucous can be seen in the trachea. Sometimes, there may be presence of casts or plugs in the air passages of the lungs and cloudiness of the air sacs. Lungs may be congested. In the viscerotropic velogenic form of disease, which affects the digestive tract, lesions include presence of haemorrhages in proventriculus, especially at the tip of proventriculus glands, and necrotic lesions or ulceration elsewhere in the intestinal tract especially involving the region of caeca and caecal tonsils.

Vaccination and Prevention:

            Vaccination is the recommended method for prevention. Use of the mild live virus vaccines called as the B1and LaSota commonly done for prevention of the disease. The vaccines are applied into the nostril or eye or added to the drinking water or applied in the form of spray. Broiler chickens are usually vaccinated when seven to ten days of age. Chickens kept for egg production are usually vaccinated at least three times. The vaccine is given when birds are approximately seven days, again at about four weeks and a third time at about four months of age. Revaccination while in lay is commonly practiced. There is no treatment for Newcastle disease. Good management programs and good “biosecurity” measures may reduce the occurrence of Newcastle disease virus.

Infectious Bronchitis

Infectious bronchitis caused by corona virus is an extremely contagious acute respiratory disease of chickens. The disease is characterized by coughing, sneezing and respiratory rales (rattling).In young chickens, there is severe respiratory distress occur. In layers, respiratory distress, nephritis, decrease in egg production, and loss of internal quality and external egg quality are reported.

Spread:

The disease is transmitted by aerogenous route. Other modes of spread of virus include spread by mechanical means such as clothing, poultry crates and equipment. The disease is also spread by droplet infection through the air, from bird to bird. The virus may also be spread by contaminated material and equipment, and via faeces.

Clinical Signs:

           There many different strains of the virus and can affect different organ systems like respiratory tract, reproductive tract and kidneys. In broilers, the infection is mostly confined to the respiratory system. Symptoms are difficulty in breathing, gasping, sneezing, rales and watery nasal discharge. In chickens under three weeks of age, mortality may reach thirty or forty percent. In birds over five weeks of age, this disease does not cause a significant mortality. Feed consumption decreases sharply and growth is retarded. When infectious bronchitis occurs in a laying flock, production usually drops to near zero with a few days. Four weeks or more may be required before the flock returns to production. Some flocks never regain an economical rate of lay. During an outbreak, small, soft-shelled, irregular-shaped eggs are produced.

Lesion:

The trachea, sinuses, and nasal passages may contain serous, catarrhal, or caseous exudates and the air sacs have foamy exudates initially, progressing to cloudy thickening. Birds infected when very young may have cystic oviducts, whereas those infected while in lay have an oviduct of reduced weight and length and regression of the ovaries. Infection with nephropathogenic strains results in swollen, pale kidneys, with the tubules and ureters distended with urates; in birds with urolithiasis, the ureters may be distended with urates and contain uroliths, and the kidneys may be atrophied.

Vaccination and Prevention:

Vaccination is practiced for chickens being retained as layers. Use of the killed virus vaccines called the LaSota strain commonly done for prevention of the disease. Vaccine is usually added to the drinking water, but may be dropped into the eye or nostril or used as a spray. Biosecurity protocols including adequate isolation, disinfection are important in controlling the spread of the disease

Avian Influenza

The disease is caused by orthomyxovirus type A. This is highly zoonotic disease and can infect domestic poultry and other birds. Avian influenza viruses can cause either mild or severe viral infections depending upon whether the infection is by highly pathogenic avian influenza virus or low pathogenic avian influenza virus. The mild form of illness is categorized by listlessness, loss of appetite, respiratory distress, diarrhea, transient drops in egg production, and low mortality. The highly pathogenic form produces facial swelling, blue comb and wattles, haemorrhages seen as dark reddish spots on shanks and legs, dehydration along with respiratory distress. Mortality can reach 100 percent in case of infection by highly pathogenic avian influenza viruses. Egg production and hatchability decreases drastically.

Spread:

           Direct contact with the infected birds. Avian influenza can be spread by contaminated shoes, clothing, crates, and other equipment. Insects and rodents may mechanically carry the virus from infected to susceptible poultry. The avian influenza virus can remain viable for long periods of time at moderate temperatures. As a result, the disease can be spread through improper disposal of infected carcasses and manure.

Clinical Signs:

           The main symptoms are depression, loss of appetite, cessation of egg laying, nervous signs, swelling and blue discoloration of combs and wattles due to disturbance of blood circulation, coughing, sneezing and diarrhea. Sudden death can occur without any previous signs. The mortality rate may reach up to 100% depending on the species, their age, the virus type involved and environmental factors like concurrent bacterial infections.

Lesions:

Necrotic foci present in the visceral organs and also show oedema, hemorrhage, and hyperemia and also there is perivascular lymphoid cuffing. Parenchymal degenerations and necrosis occur in spleen, kidney and liver.

Vaccination and Prevention:

There is no effective treatment for avian influenza. With the mild form of the disease, good husbandry, proper nutrition, and broad spectrum antibiotics may reduce losses from secondary infections. A vaccination program used in conjunction with a strict quarantine has been used to control mild forms of the disease, strict quarantine and rapid destruction of all infected flocks remains the only effective method of stopping an avian influenza outbreak.

Infectious laryngotracheitis

It is a viral disease of chicken caused by alpha herpes virus and it is a disease of respiratory track which also may result in severe production losses due to mortality and there is also decrease in egg production. The virus only affects the respiratory tract and strains vary in virulence. Fowls of all ages are susceptible, the disease mostly seen in field conditions in birds from 3-9 months old.

Spread:

The virus is present mainly in the exudate from the nares, oropharynx, trachea and the conjunctiva. Infection is spread in aerosol from infected birds, i.e. through the upper respiratory and ocular routes. It enters the body through the upper respiratory tract and conjunctiva. Ingestion can also be a mode of infection.

Clinical Signs:

            Clinical signs generally appear 6-12 days following natural exposure. Characteristic clinical signs include nasal discharge and moist rales followed by coughing, gasping, sneezing, depression and conjunctivitis. When severe epizootic forms of the disease occur, signs also include labored breathing and expectoration of blood-stained mucus; and upon gross examination of the trachea, severe hemorrhages and mucus plugs are characteristics.

Lesions:

             Gross lesions are observed in the larynx and trachea, and tissue changes include sinusitis, and mucoid tracheitis or severe, hemorrhagic tracheitis even though the conjunctiva and other respiratory tissues could be also been affected. In severe forms, degeneration, necrosis, and hemorrhage occur in later stages. Inflammation may extend down the bronchi into the lungs and air sacs. Multinucleated cells are formed and lymphocytes, histiocytes, and plasma cells migrate into the mucosa and submucosa after 2-3 days. Intranuclear inclusion bodies are found in epithelial cells by 3 days. Inclusion bodies generally are present only in the early stages of infection and they disappear as infection progresses, a result of the necrosis and desquamation of epithelial cells.

Vaccination and Prevention:

Vaccination is done with live attenuated vaccines and viral vector recombinant vaccines. Application of biosecurity measures will avoid exposing susceptible chickens via contaminated fomites. The importance of site quarantine and hygiene in preventing the movement of potentially contaminated personnel, feed, equipment, and birds is central to successful prevention and control of ILT.

References

Shanker, B. P.2008. Common Respiratory Diseases of Poultry. Veterinary World, Vol.1 (7): 217-219.

Swayne, D. E., Glisson, J. R., McDougald, L. R., Nolan, L. K., Suarez, D. L. and Nair, V.2013.Diseases of poultry. American Association of Avian Pathology, 13^th edition.