Viral diseases are one of the major diseases that affect chickens yearly. So, as a poultry farmer, it’s your job to watch out for these diseases and keep your poultry safe from them. In this article, most of the viral diseases of chicken will be stated out and you’ll be enlightened on everything you need to know about them and their prevention.
1. Newcastle disease
Newcastle disease is a highly contagious viral infection in several species of fowl including chickens and turkeys that causes a respiratory nervous disorder. Various types or strains of the virus have been identified. They differ in their capacity to induce nervous disorder, visceral lesions, and death.
The most chronic strain is the Viscerotropic Velogenic Newcastle Disease (VVND).
It can also be referred to as “Exotic Newcastle Disease,” and susceptible fowl infection with this form generally results in high mortality.
A lighter type of illness is called mesogenic Newcastle disease.
Newcastle is a highly infectious illness. Normally all the birds in a flock get infected between three to four days.
Recovered birds also aren’t regarded carriers and the virus doesn’t usually live on the premises for more than thirty days.
Method of transmission: Contaminated equipment and clothing, contact with an infected bird, through air especially during the active respiratory stage.
Signs/symptoms: In young chickens, signs exhibited include; difficulty in breathing, nervous disorders, sneezing, gasping, paralysis of wings and legs, twisting of head and neck, mortality which may differ from none to complete loss of the flock.
In adults, the rate of respiratory problems is higher.
Symptoms include; nervous disorders, quick reduction on egg production, production of small, soft and irregular shaped eggs, nasal discharge, mucous in the trachea, plugs in air passages of the lungs, cloudiness in the eye cornea and mortality though it is usually low.
Indications of the respiratory nervous disorder as well as other typical lesions could be sufficient for a course of treatment to be made.
Treatment: Newcastle disease has no treatment. Even the best management programs are not always respected by the disease but good “biosecurity” practices will help minimize the chances of exposure to Newcastle disease virus.
Control and prevention:
The most effective way to prevent the disease is by vaccination.
There are several types of vaccines available but the mild live virus vaccine known as the types B1 and La Sota are the most successful and widely used.
Method of application and when to apply:
The vaccines may be used by dropping into the nostril or eye, drinking water or by spraying.
Chickens are usually vaccinated when they are between seven and ten days old. Chickens kept for the development of eggs are commonly at least three times vaccinated. The vaccine is administered when birds are about seven days old, then at about four weeks old and a third time at about four months old. Revaccination is typically done when in the chicken is inlay position.
2. Avian pox as one of the Viral Diseases of chicken
Avian pox is a viral infection in birds that is relatively slow to spread, identified by wart-like nodules on the skin and diphtheritic necrotic membranes lining the mouth and upper respiratory tract. It has been evident in birds since the very beginning of history. Mortality is generally not significant unless there is a mark on the respiratory involvement. The disease can happen at any bird’s age, at any time.
Avian pox is caused by a virus that has at least three species or types; fowlpox virus, pigeon pox virus, and canarypox virus.
Natural pox is considered to be caused by fowlpox virus in chickens, turkeys, and other domestic fowls.
Fowlpox can be spread through either direct or indirect contact. In dried scabs, the virus is extremely resistant and may survive on polluted premises for months under certain conditions. A number of species of mosquitoes can transmit the disease. Mosquitoes can carry infectious virus after feeding on affected birds for one month or more. After the virus has been introduced, it spreads through direct or indirect contact within the flock or by mosquitoes. Recovered birds don’t remain carriers.
Since fowl pox usually spreads slowly, it could affect a flock for several months. It takes three to five weeks for the disease to move in the individual bird.
The disease is reflected in one or two ways, either cutaneous pox (dry) or diphtheritic pox (wet form).
Wet pox, in particular larynx and trachea, is associated with the oral cavity and the upper respiratory tract. The lesions are diphtheric in character and usually involve the mucous membranes to such an extent that an ulcerated or eroded area is left after removal.
Dry pox begins with small whitish foci, which develop into wart-like nodules. Eventually, the nodules(irregular growths) are shed, and the formation of scab precedes the final cure. Lesions are most often found on the body’s featherless sections (comb, wattles, ear lobes, lips, and sometimes feet).
Signs and symptoms: Stunted growth, reduction in egg production, poor feeding rate, difficulty in breathing, lesions on face, and feet.
Treatment: Unfortunately, there is no treatment for fowl pox. But it can be controlled.
Disease control is best achieved by preventive vaccination since it is not prevented by ordinary management and sanitation practices. There are many types of vaccines available, and they are safe if adequately administered.
Broiler vaccination is generally not required unless the mosquito population is high or infections have recently occurred. Using the wing-web system and using a one needle applicator, the chicks can be vaccinated as young as one day. When the birds are six to ten weeks old, all the replacement chickens are vaccinated against fowl pox.
Single-use of the vaccine against fowl pox results in lifelong immunity.
3. Infectious bronchitis
Infectious bronchitis in chickens is a highly infectious respiratory disease.
It is known to be the most infectious disease in poultry. When it develops, all vulnerable birds on the premises become sick, irrespective of measures regarding sanitation or quarantine.
It is caused by a virus that only affects the chickens. This virus can not affect other fowls or laboratory animals. There are several distinct virus types.
The disease is not spread by the egg, so when poultry is not present, the virus can survive in the house for potentially no more than a week. Heat and ordinary disinfectants easily break it down.
The infection confines itself to the respiratory system.
Signs/symptoms: Coughing, sneezing, rattling, difficulty in breathing, slight watery nasal discharge, reduction in feed consumption, stunted growth, reduction in egg production, production of small, thin, and soft-shelled irregular-shaped eggs and high mortality in young chicks.
It’s hard to differentiate infectious bronchitis from most of the other respiratory diseases. As a result, a clearly defined clinical diagnosis requires an analysis by the research lab.
Treatment: There is no treatment for infectious bronchitis. Although, for younger chicks, increased room temperature can be helpful.
Control/prevention: Vaccinate the chickens with the guidance of your local vet.
Numerous vaccines are available in the market.
Many represent a selected or modified form of the infectious bronchitis virus.
The vaccine used should contain viruses commonly observed to exist in the environment.
All vaccines contain live viruses and many of those that provide excellent defense is also able to cause symptoms and reduce the development of eggs. The vaccine virus propagates to other susceptible birds. Usually, the vaccine is applied to the drinking water, but you can also drop some of it into the eye or nostril of the chicken or use it as a spray in the poultry house.
4. Lymphoid leukosis as one of the Viral Diseases of chicken
Lymphoid leukosis is a disease of adult chickens. Although lymphoid leukosis virus can produce blood, bone, and lymph responses, the lymphoid response to the tumor is more common.
Method of transmission: Through eggs and feces, from infected birds to weak ones through bloodsuckers like mosquitoes, during fowlpox vaccination.
Clinical diagnosis of lymphoid leukosis is based on the history of the flock and symptoms of the disease. The lymphoid condition can not be easily differentiated from the visceral reaction to Marek ‘s disease; but, in the differential diagnosis, there are some features that help to identify it.
Signs/symptoms: Tumors present in the liver, spleen, ovary, and lungs, loss of appetite, weight loss, diarrhea, poor egg production, and death.
Treatment: The disease has no treatment but can be prevented.
Control/prevention: Buy resistant bird species, as genetic resistance is a constraint. Do not keep birds of different ages together, let the younger birds be separated from older birds. Disinfect the incubator and keep it clean. Avoid stressing the chickens and control blood-sucking parasites in the brooder.
5. Gumboro or Infectious Bursal Disease
The infectious bursal disease is a severe viral disease of young chickens which is highly contagious. It is most commonly found in the areas rearing highly concentrated poultry.
Method of transmission: Direct bird to bird contact, contaminated air, equipment, feed, litter, and feces, from infected insects, wild birds, and humans to the chicken.
Though this disease causes serious damages, its impact on reducing the ability of the bird to develop immunity to other diseases is perhaps the most serious effect this disease produces.
Signs/symptoms: Marked morbidity and mortality in birds, ruffled feathers, loss of appetite, difficulty while excreting, slight tremor, dehydration, unsteadiness, confused movements, whitish diarrhea, high/extremely low body temperature, prostration, post mortem lesions like changes in skeletal muscle, liver, kidneys, and bursa, oblong shape of the bursa, the formation of a gelatinous film around the bursa, death.
Infectious bursal disease treatment depends on flock history and post mortem lesions. The assessment may be substantiated through laboratory procedures.
Treatment: There is no exact treatment for Gumboro.
Prevention/control: Facilitating measures are advantageous, such as raising the heat, proper airflow/ventilation, and water consumption.
Vaccines have been developed but need to be used with caution. Good immunity will build if issued appropriately.
6. Marek’s Disease Virus (MDV)
Marek ‘s disease is a disease of young chickens but it can also affect older birds. Contrary to the tumor response to lymphoid leukosis, Marek ‘s disease can be found in more diverse environments.
It appears the virus is concentrated in the follicles of the feather and sheds in the dander (sloughed cells of the skin and the feather). In dander, the virus has a long survival time since the viable virus can be isolated from houses which have been depopulated for several months.
Young birds are most vulnerable to Marek’s disease infection; but, because the incubation period is minimal, clinical symptoms may occur much earlier than it does for lymphoid leukosis.
Marek ‘s disease can yield a number of clinical responses, all of which are lymphoid in nature. There are acute visceral, sensory, ocular, skin, or variations of the observable responses.
The most severe losses in broilers are due to skin leukosis. The losses at the processing plant result from heavy condemnations. A typical lesion is the widening of the feather follicles due to lymphocyte aggregation. This is the most infectious virus as it is developed in feather follicle regions and is shed with skin dander.
Ocular leukosis or grayish-eye is typically seen at early maturity. Mortality rates are usually low in some flocks but may be close to 25 percent. The spotty depigmentation or diffuse graying of the iris in the eye is indicative of this. The pupil forms an unusual shape and does not respond to illumination. Diarrhea of emaciation and death result.
Method of transmission: The normal method of transmission is through aerosols that contain contaminated dander and dust.
Signs/symptoms: Large internal tumors, lesions on gonads, liver, spleen, kidney, heart, muscles and lungs, paralysis of wings, neck, and legs, weight loss, diarrhea, anemia, difficulty in breathing, and death.
Treatment: There is no cure for Marek ‘s disease as is the case for lymphoid leukosis.
Nevertheless, the lesions may degenerate in some cases, and clinically affected birds might well make significant recoveries.
Control/prevention: There is a vaccine available that is up to 90% successful in preventing Marek ‘s disease. It is given as a subcutaneous injection to day-old chickens when the birds are in the hatchery. The use of the vaccine should be in a clean area and requires strict compliance with manufacturer’s guidelines.
7. Avian influenza
Avian influenza is a highly contagious disease that can lead to 100% mortality in birds.
The disease is caused by a virus known as Orthomyxoviridae.
All bird species are vulnerable to the disease but outbreaks in turkeys and chickens occur more frequently.
Influenza viruses have two surface proteins, haemagglutinin, and neuraminidase, which decide their subtype and the species of animals they affect.
When AI viruses of two types of haemagglutinin, H5, and H7, infect domestic poultry, they often evolve and lead to virulent diseases in these birds, which are called highly pathogenic avian influenza (HPAI). The initial infection that stimulates none or minimal illness is called low pathogenic avian influenza (LPAI).
Birds from wild water serve as reservoir carriers of influenza viruses, but the viruses in these birds do not usually cause disease.
Environmental factors have a pronounced effect on the out-of-bird virus survival. Avian influenza virus can live in manure for at least 35 days at 4 ° C and can be isolated from water in the lake. The virus can survive at ambient temperature for up to 23 days when stored in the fridge, and for several days in animal carcasses. The virus may persist in products made from poultry meat but is eradicated by cooking.
Method of transmission: Direct or indirect contact with infected birds, contact with infected equipment, contaminated eggs, litter, and drinking water.
Signs/symptoms: Depression, a sudden rise in mortality rate, fast breathing, reduction in the poultry’s egg production and production of soft-shelled eggs, watery diarrhea, blue discoloration of comb and wattles, swelling of the face, and sudden death.
Treatment: Vaccination and disposal of infected birds
Prevention/control: Bio-security program, treatment of drinking water, quarantine method, cull diseased birds immediately.
8. Avian Encephalomyelitis
AE is a viral illness of the poultry’s central nervous system, particularly chickens, and turkeys.
It is caused by a picornavirus.
The disease is most common among 1-6-week-old chickens. Symptoms typically begin at age 7-10 but may be present at hatching or slowed down for several weeks.
Recovered birds are immune, and the virus does not continue to spread.
Method of transmission: Vertical transmission, direct contact with infected birds, infected droppings.
Signs/symptoms: Tremors of the head and neck, drop on egg production, high mortality rate, loss of muscle coordination, dull eyes, unsteadiness, weakness, paralysis, reduction in feed and water intake, loss of weight, death.
Treatment: There is no treatment for Avian Encephalomyelitis.
Control/prevention: Vaccination, cull diseased birds, dispose off and burn dead birds.
9. Chicken Anemia Virus Infection (CAV)
CAV is an acute viral infection of chickens. It is a small DNA virus.
It can infect birds of different ages but mostly affects young chickens.
CAV deprives the immune system and as such makes infected birds more prone to other diseases. Mortality may also result from secondary infections.
Vaccinated birds have antibodies that neutralize them against further infection.
Chicks from resistant breeder hens will be secured by maternal antibodies until they are able to develop their own resistance. Defense by maternal antibodies could however be surpassed if another extreme immunosuppressive disease affects the chick, such as infectious bursal disease, Marek ‘s disease, or reticuloendotheliosis.
Method of transmission: From parent to offspring, Fecal-oral transmission, contact with the diseased bird.
Signs/symptoms: Anaemia, depression, hemorrhage, incompetence, high mortality rate.
Treatment: Antibiotics can be administered.
Control/prevention: Bio-security practices, maintaining good hygiene, vaccination, proper management generally.
10. Egg drop syndrome (EDS)
EDS is a result of a viral infection in layers.
This leads to a sudden decrease (10-40 percent) in the production of reported eggs or an inability to meet the normal production rates. The early stages of the disease can be difficult to identify, as hens eat the shellless eggs, and the only proof that can remain are the membranes.
Failure to reach estimated production targets is noticed in flocks where certain birds have obtained immunity as a result of the spread of the virus.
Chickens of all ages are vulnerable but the disease is most intense in broiler breeders and layer strains of brown-eggs. EDS was first introduced by infected vaccines into chickens and transmitted through breeder flocks.
EDS can be differentiated from Newcastle disease and influenza virus infections due to the absence of disease, and from infectious bronchitis due to changes in the eggshell that develop at or just before egg production decreases.
Method of transmission: From parent to offspring, contaminated egg trays, infected droppings, contact with infected wild birds, contaminated vaccination needles, and farm equipment.
Signs/symptoms: Production of soft-shelled and shell-less eggs, drop in egg production, diarrhea, loss of shell color.
Treatment: There has not been any successful treatment for EDS.
Control/prevention: Good bio-security methods, clean and disinfect egg trays before use, avoid your birds coming in contact with other birds especially waterfowl, give them clean water to drink, practice good hygiene, vaccination.
11. Infectious Laryngotracheitis as one of the Viral Diseases of chicken
It is an extremely contagious disease of chickens caused by a herpes virus.
Disinfectants, fumigants, and direct sunlight can quickly kill the virus but it can survive in the infected litter for up to two days and in dead birds for about a year.
The disease tends to occur in high broiler farm density areas, and vaccination may be the only control means.
Method of transmission: Direct contact with infected birds (dead or alive), contact with contaminated bird tissue, contaminated equipment, infected humans, and animals.
Signs/symptoms: Drastic drop in egg production, high mortality in young birds, watery eyes, difficulty in breathing, watery discharge from the nose, sneezing, and coughing of blood or mucous.
Treatment: Antibiotics can be used to control infection and reduce losses.
Control/prevention: Vaccination, good bio-security measures, incinerate dead birds.
12. Lymphoid Tumour Disease (Reticuloendotheliosis)
Lymphoid Tumour disease is a retrovirus illness usually found in chickens, turkeys, ducks, geese, and quails with morbidity levels of up to 25 percent.
Method of transmission: From ovary to egg, from mosquitoes to birds, contaminated vaccines i.e Marek’s Disease vaccine.
Signs/symptoms: High mortality rate, weight loss, weakness of the legs, diarrhea.
Treatment: The disease has no treatment but can be controlled.
Control/prevention: Bio-security program, avoid live vaccine contamination.
13. Viral Arthritis (Tenosynovitis) as one of the Viral Diseases of chicken
Tenosynovitis is triggered by reoviruses, and the clinical symptoms and signs of the virus differ significantly based on its pathogenicity.
Viral arthritis is a common form of chicken reovirus infection, and there are at least 5 viral serotypes. Morbidity is high but, usually, mortality is lesser.
Method of transmission: Fecal-oral
Signs/symptoms: Malabsorption syndrome, reduced mobility, and growth, sickly appearance, swelling, hock inflammation, lameness, pericarditis disease.
Treatment: Vaccination (live and inactive vaccination)
Control/prevention: Good bio-security program, maintain good hygiene, proper management.
As a good poultry farmer, the safety of your chickens should be your priority, you must apply the above necessary measures to prevent/reduce losses.