When the disease affects the nasal passages, these can become blocked, causing labored breathing and, as a result, lethargy and loss of appetite in the sick bird.

Injuries to the corner of the beak force the bird to keep its beak open at all times; this is a warning sign for the bird keeper that something is wrong with the bird.

Eyelid lesions cause the eye to water continuously; the eyelids may become stuck together due to the abundant, thick discharge.

Diagnosis of diphtheria:

The first thing we need to keep in mind is that, based on the lesions we see, we might think it’s diphtheria, but we must remember that there are other diseases that present similar lesions. We need to keep this in mind and check for them first; examples.

• Vitamin A deficiency: The membranes or small lesions that form do not leave behind bleeding ulcers when they slough off.
• Sporadic pseudodiphtheria: It has the character which gives the name of sporadic, appearing only in one, two or three birds, but you never have the character diffusive of diphtheria.
• Stomatitis: caused by fungi, it is not usually widespread or diffuse and is localized in the esophagus, though it may extend into the crop.
• Aspergillosis The coatings nasal have a greenish color.
• Contagious coryza: Although the eyes exhibit caseous lesions, the membranes, when they detach, do not leave ulcerative beds.

The onset of this disease in an exploitation was due to the introduction of animals that are sick or in an incubation period.

The agent that determines the disease is a virus-type filtrable, which according to its location in the body produces smallpox and diphtheria as isolated forms and in other cases as a mixed form of both.

The virus is highly contagious, making it easy for healthy birds to become infected; as a result, fowl pox is a common disease in chicken coops.

The latent virus remains in the birds' bodies without causing any symptoms; it is only when certain factors—such as rain, cold weather, or other diseases (e.g., parasites)—trigger the onset of the disease.

The virus can enter a bird’s body through the mouth when it drinks or eats contaminated food, but the easiest route of entry is through skin abrasions caused by pecking, spurs, or small accidental wounds.

The transmission from animal to animal is occasionally a directly through skin wounds or mucous membranes.

The symptoms of the dipteran-fowl pox vary according to the form in which it appears.

The presentation can be in one of three ways:

Cutaneous form:

The first indication of the infection is the appearance, in the crest, and the chins, mainly of small spots of gray vesicular. These they dry quickly, forming crusts that will enlarge gradually, and they may join with lesions adjacent to form the largest eruption with the appearance of warts.

If the scabs are picked off (which should not be done to avoid spreading the virus), the underlying surface appears rough and bloody. These lesions may occur in small numbers or be so numerous that they cover almost all of the unfeathered skin on the head, including the crest, wattles, face, eyelids, earlobes, and corners of the mouth.

Rashes may also appear on the legs and toes, around the anus, and under the wings. The scabs covering the lesions persist for some time—between three and four weeks—and then gradually fall off, leaving a grayish scarred area. Birds affected by this type of disease may show few or no symptoms if the infection is mild.

In summary, it is characterized by the presence of wart-like lesions on the featherless parts of the body, located mainly on the head—particularly on the crest, wattles, edges of the eyelids, corners of the beak, toes, and legs.

Form diphtheria or of the throat:

The way díptera of the disease is characterized by the formation of plaques yellow, outgoing, and membranous in the mouth and throat. These portions of necrotic tissue are strongly adhered to, and if you get up forcing them to become vicariously, they leave a rough surface bleeding.

As the disease progresses, the plates become larger, thicker, and consistency, cheesy, and sometimes extend both to prevent the bird to close the mouth.

The presence of plaques in the larynx, or close to it can make breathing difficult, and to do that it is accompanied by grunting noises. If it is difficult in any degree to the ingestion of food, the birds soon lose weight and have a general look weak.

It is not uncommon for affected eyes, characterized initially by the inflammation of the membranes and the presence of distillation in water. This phase is often followed with the formation and accumulation of pus yellow and pasty, which makes the eye to swell and look bulky. 

In short: it Is manifested in the form of plates, membranous in the mouth and throat, nodules opaque in the mucous membranes of the respiratory tract and digestive, eyes and eyelids.

Mixed form:

In this form, lesions appear equally on both the skin and the mucous membranes.