This article includes the lecture prepared by Dr. Alphonse Gnanarajan for the XXXI International Symposium of Biovet in Tarragona, 2018, which took place on May 29th, 2018. Under the title, “Main avian pathologies found in India” Dr. Maria Soriano, of the technical team of Biovet SA, who replace Dr. Alphonse Gnanarajan, presented the 10 main avian diseases in India.

MAIN POULTRY DISEASES – TOP 10

• MAREK’S DISEASE (MD)

Marek’s disease is a neoplastic disease caused by an oncogenic herpesvirus. The virus infects lymphocyte cells that, in some cases, will become tumour cells and infiltrated in different organs and tissues of the animal.

It has a worldwide distribution, so it could be said that all birds end up being exposed to the virus, although only a few cases develop the disease, usually the ones that are still very young and are not vaccinated or if there is a vaccinal failure.

Infected animals without symptoms are of primary importance since they are the ones that cause greater economic losses, due to poor growth of the animals, loss of uniformity and quality of the carcass, reduction in egg production, greater susceptibility to other diseases and worse response in other vaccinations.

Symptomatology depends on the location of the tumours and appears in the rearing animals that are almost ready for production. There are three types of presentation of the disease: cutaneous, nervous or visceral.

The cutaneous presentation appears as nodules at the level of the follicles of the feathers.

Nervous presentation shows different signs depending on the peripheral nerve in which the lymphocytic infiltration occurs, although the most frequent is to observe flaccid paralysis of the legs due to unilateral affection of the sciatic nerve or blindness due to the effect of infiltration on the nerve.

The visceral presentation with nodular lesions is what causes the general disorders and death of the animal.

• NEWCASTLE DISEASE (RD)

It is a highly contagious disease, caused by an avulavirus, in which the usual form is a respiratory condition, but other main clinical signs may include nervous manifestations (depression, drooping wings, twisted head or paralysis), diarrhea and swelling of the eyes and the neck.

Its importance lies in the mortality and the low productive yield an outbreak could cause, since it may lead to a partial or total stop in egg production and rough or thin egg shells.

This pathology, also known as Ranikhet disease in India, shows diphtheritic hemorrhagic lesions of the alimentary tract, mainly in the ceca and cloaca, in its viscerotropic presentation. It is also common to find edema and petechiae in the gizzard and hemorrhagic ovaries.

• INFECTIOUS LARYNGOTRACHEITIS 

It is a respiratory disease caused by a herpesvirus that could appear in different presentations: peracute, subacute or chronic. Due to this, clinical signs vary from an extreme severity, with deaths by asphyxia, to a very mild symptomatology, that is not possible to differentiate from other respiratory diseases.

This virus causes fibrinous and hemorrhagic infiltration of the respiratory tract, so the presence of blood in the trachea, sinuses and oral cavity makes breathing difficult. In the postmortem examination, fibrinous, necrotic, caseous and/or diphtheritic plaques and plugs are found in the trachea, larynx and mouth.

• GUMBORO DISEASE (IBD)

Gumboro disease, also known as infectious bursal disease (IBD), is an acute viral infection, caused by a birnavirusthat, as one of its names indicates, it mainly affects the Bursa of Fabricius, destroying the immature B lymphocytes of young animals.

Clinically, it is observed in chickens between 3 and 6 weeks old, which show depression and diarrhea. This diarrhea is the cause of dehydration, that affects the kidney and may cause the death of the animal.

Younger birds suffer from a subclinical disease causing immunosuppression, and thus increasing susceptibility to secondary infections and decreasing effectiveness of vaccines and productive parameters.

In cases showing clinical signs of the disease, diffuse hemorrhagic lesions are often observed in pectoral muscles and thighs. Hemorrhages and erosions may also appear at the level of the proventriculus-gizzard junction, as well as different degrees of nephritis or nephrosis.

Lesions at the level of the Bursa of Fabricius are variable and depend on the evolution of the disease. Initially, it is enlarged and edematous, around 5 days post-infection it returns to its normal size, although it can be hemorrhagic until it finally atrophies.

• INFECTIOUS BRONCHITIS (IB)

This viral disease, exclusive of chickens, is confined to the respiratory system and the urogenital tract. There are different strains of the virus, with greater or lesser affinity for the systems named before. This virus has high mutagenic capacity, hence the main difficulty to fight against it, because vaccination does not guarantee to be resistant to the disease.

Most visible signs are those of the upper respiratory tract (sneezing and nasal discharge), but the condition of the ovaries is of greater importance, since it produces a marked decrease in the egg production and an increase in poor quality eggs (deformed or without shell). When kidneys are affected, a significantly increase in water consumption may appear, resulting in watery stools and wet litter.

According to all that it is mentioned above, the most frequent lesions caused by this disease are: serous, hemorrhagic, catarrhal or caseous exudate in trachea; pneumonia and/or opaque air sacs with possible caseous material; atrophied ovary and inflamed oviduct and interstitial nephritis, where kidneys are enlarged and pale.

• INFECTIOUS CORYZA (IC)

Infectious coryza is a highly contagious bacterial disease produced by Avibacterium paragallinarum. It shows mainly rhinitis and infraorbital sinusitis, seen as facial edema in this area.

Conjunctivitis and abundant nasal and ocular secretion that may cause eyelids adherence could also appear. Usually, this state is accompanied by decreased consumption of food and water, and in laying birds, by variable reduction of egg production. Low respiratory tract infection rarely occurs.

• CHRONIC RESPIRATORY DISEASE (CRD)

It is a contagious disease, with slow development and prolonged course, caused by bacteria of the genus Mycoplasma spp. Affected animals develop respiratory symptoms such as sneezing, nasal discharge or dyspnea.

In broilers, mortality rate may be low in cases without complications, but could reach 30% in cases complicated with other bacteria or viruses. There are also collateral losses due to stunted growth and sacrifice before reaching the term. Mortality can be low in layers; however, it causes a drop in the laying rate.

Lesions that appear are very variable, depending on whether there are other concomitant infections or not and on the mycoplasma agent itself. Sinusitis, tracheitis, air sacculitis, thickening and turbidity of the alveoli, exudative accumulations, fibrinopurulent pericarditis and perihepatitis could be observed.

• FOWL CHORERA or AVIAN CHOLERA

It is a contagious bacterial disease, caused by Pasteurella multocida, which affects adult birds or birds in the period of sexual development, that consists of 3 clinical presentations:

• PERACUTE FORM: Development of sudden deaths without previous symptoms. It is not frequent nowadays due to the immunization of breeders.
• ACUTE FORM: It has a course of 1-2 days, where the birds show anorexia, fever, depression, profuse white or grayish diarrhea, respiratory difficulty with abundant mucus, and cyanosis visible on crests and wattles.
• CHRONIC FORM: Animals remain sick and cachectic for a long time, with purulent or caseous inflammation of the wattle and possible subcutaneous abscesses.

Mortality and morbidity are variable and may affect a high percentage of animals. Acute cases that survive tend to evolve towards chronicity. Avian cholera causes very high economic losses due to high mortality, decreased posture and reduced fertility of hatching eggs. Outbreaks occur during low temperatures and high humidity (late summer, autumn and winter).

Necropsy findings seen in an acute outbreak lesions look like hemorrhagic septicemia, with petechiae and generalized hemorrhages in organs and skin, congestive spleen without splenomegaly, milliar necrosis in the liver and edematous lungs, sometimes with small purulent grayish areas. Caseous masses may appear in the air sacs and/or in the peritoneum in chronic presentations.

• COCCIDIOSIS

Avian coccidiosis is a parasitic disease caused by protozoa of the genus Eimeria, originating a clinical or subclinical process characterized by bloody diarrhea and decreased production. There may also be a certain degree of dehydration, blood stained cloaca and anemia.

Destruction of the epithelial cells and the villi is what leads to a malabsorption syndrome that causes the loss of productivity of the infected animals. In addition, these lesions enable the action of other pathogens, such as Clostridium.

There are 7 species of Eimeria identified as pathogens of chickens, all located in the small intestine, except E. tenella, which is located in the caecum. Because of that, different lesions could be observed depending on the type of Eimeria and its virulence. Most of clinical outbreaks are due to mixed infections of several species of Eimeria and, therefore, lesions are observed in different areas of the intestine.

This protozoon causes enteritis of different severity, usually hemorrhagic, that is visible externally as petechiae. Species located in the cecum cause hemorrhagic typhlitis, with fresh or clotted blood mixed with fibrous exudate.

• FOWL POX or AVIAN POX

It is a moderate to severe viral disease, with a slow development, caused by a poxvirus.

This virus induces a rapid growth of superficial layers in the skin and mucous membranes that form masses of proliferative tissue. The disease has two presentations depending on its location: cutaneous or “dry” from, on the skin without feathers, or diphtheric or “wet” form, in the alimentary and upper respiratory tract. Both could evolve alone or simultaneously. Diphtheria injuries are more serious, as they can cause death from suffocation or starvation.

Infection may occur at any time of the year, however, is believed to exist an association between outbreaks of the disease and climatic conditions favorable to the abundance of mosquitoes, with rains and warm temperatures.

Lesions vary according to the stage of development: papules, vesicles, pustules, or crusts, mainly in the region of the head. Diphtheric lesions are yellowish or whitish plaques that grow on the mucous shells of the nasal and buccal cavities, sinuses, larynx, pharynx, trachea or esophagus.

CONCLUSIONS

After describing each disease, it could be observed that their common fact is that they all lead to a decrease in decrease in productive parameters, either because broilers do not grow at the expected rate or because egg production is not appropriate for the week of the laying period and/or the quality of the egg is worsened.

The best way to solve these problems is to anticipate them. Applying the three essential points mentioned below will allow us to prevent the outbreak of a disease or will improve our control on it:

• Apply a management, including environmental and animal density monitoring, suitable vaccination plan, etc.
• Maintain adequate hygiene conditions and control of facilities that prevent the entry of wild animals.
• Establish an appropriate nutritional plan for each period and ensure that this feed is stored in the right conditions.

* Photos provided by Dr. Alphonse Gnanarajan