Smallpox in pigeons

Smallpox in pigeons . It is a disease caused by a poxvirus (of the Avipoxvirus group ).

Summary

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• 1 Characterization
  • 1 Transmission:
• 2 clinical forms of the disease:
• 3 Diagnosis:
• 4Control:
• 5 Treatment:
  • 1 Vaccine
• 6Fuente

Characterization

17 types of Avipoxvirus have been described, all of them related. The one that affects pigeons is species-specific, that is, it only causes the disease in pigeons and birds of prey. It is a disease that is spread all over the world. The typical crusty deposits on the skin ( smallpox ) give the name to the disease.

Transmission:

Aviproxviruses cannot penetrate intact skin , hence contagion occurs through direct contact with affected birds or contaminated material, through skin or mucosal wounds, or from vectors ( mosquitoes and hematophagous mites ). That’s why the disease is most prevalent in late summer , fall , and early winter , when mosquitoes are abundant. A mosquito that feeds on an infected bird can retain the infective virus in its glands .salivaries from 2 to 8 weeks. In addition, Avipoxviruses are very resistant to environmental factors such as desiccation, sunlight and chemical disinfectants.

They can survive in contaminated soil for up to 1-2 years. In the transmission of the virus, wild pigeons, hematophagous insects and man play an important role as contaminating agents. Birds of all ages are susceptible, but the youngest are the most frequently affected. Birds in the recovery phase act as asymptomatic carriers and eliminate the virus through feces, feet, feathers , saliva ., nasal secretions, tears and crop milk. Chicks can be infected by their parents who sometimes act as healthy carriers. The disease can remain dormant for years, particularly in flocks of large pigeons. No specific stressors have been described that are associated with the reactivation of the virus, it being possible to mention the effort of breeding, feathering, competitions, etc. Avipoxviruses also produce moderate depression of organic defenses, which enhances secondary infections.

Clinical forms of the disease:

Avipoxvirus-induced infections vary in clinical expression according to the virulence of the virus strain, the mode of transmission, and the susceptibility of the host. The incubation period varies from 4 to 14 days, usually being 1 week. The course of the disease is generally subacute and it takes an individual 3-4 weeks to recover. Mortality is low, although 90% of the campus can become infected. A flock of pigeons requires 2-3 months to return to their normal state. Clinically the following forms are recognized:

• Cutaneous or dry form: it is the most common and benign in pigeons. It is characterized by the presence of yellowto dark brown papules and later vesicles at the level of the skin without feathers ( eyelids , corner of the beak, cere, legs and around the cloaca). In a few days these lesions enlarge and several of them may coalesce. Subsequently, they open spontaneously, dry out and form scabs, which require several weeks to spontaneously desquamate. They usually heal without scarring. Bacterial or fungal complications are also frequent and can alter the classic appearance of the lesion, aggravating it. These lesions are very difficult to remove because of the bleeding and adherence they are.
• Diphtheria or wet form: it is characterized by nodules that coalesce and form membranous-diphtheroid-type lesions ( gray-brown and gaseous plaques), which when trying to detach them produce severe hemorrhage . They are usually located on the tongue , pharynx and larynx causing difficulty in swallowing food and respiratory symptoms. An individual may present with the cutaneous and diphtheritic forms concomitantly.
• Septicemic form: can occur in young pigeons. It is of acute presentation and high mortality (70-99%). General signs of illness are observed: embolism, anorexia, depression, weight loss, respiratory signs (from the pneumonia that occurs) and diarrhea( enteritis ). Most birds die within 3 days of developing clinical signs. Skin lesions are rare and early diagnosis of the condition is difficult. This form of the disease can also occur with very aggressive virus strains or when the birds have low organic defenses (poor diets, stress or concomitant bacterial and/or parasitic infections).
• Tumor form: some strains of Avipoxivirus are easy to produce tumors. Pigeons that survive the infection are prone to the formation of skin tumors. These are fast growing and warty in appearance and are usually dark in color; if one wishes to detach them, they are very bleeding. Surgical treatment is the only effective therapy in these cases, although they can re-form if the virus still persists in the skin. During an outbreak of the disease in a school, all the mentioned forms can coexist.

Diagnosis:

A definitive diagnosis of Avipoxvirus infection can be made by:

• Histopathology, a technique that consists of examining microscope slides of diseased organs. If smallpox is suspected, the samples of choice are: Skin and liver lesions. The sample will be positive if accumulations of viral particles in formation, commonly called inclusion bodies, appear in them.
• Culture and virus isolation can also be performed on embryonated chicken eggs.
• Blood tests are of little value in diagnosing this disease.

Control:

• Birds that recover from the disease are usually protected for at least 8 months.
• Vaccination is the best method to control Avipoxvirus infection. Because, as we mentioned, these are species specific, pigeons should be vaccinated with pigeon vipoxvirus vaccines. Commercial vaccines for these are available in Europeand the United States of America .
• All high-risk populations should be vaccinated: imported pigeons and flocks in areas with high mosquito density. Depending on the type of vaccine used, pigeons can be immunized for 6 to 12 months. It is advisable to vaccinate the entire flock after breeding is finished, when the pigeons are between 4 and 5 weeks old (December-January). In case of using live virus vaccines (those that are generally administered by brushing the feathery follicles of the thigh), it is necessary to control the post-vaccination reaction, since it shows the activity of the vaccine and the establishment of immunity. The reading is done 7-10 days after vaccination and appears in the form of small reddish pustules, surrounded by a slightly edematous area, which disappear after a week.
• Because Avipoxviruses can be transmitted by mosquitoes or hematophagous mites, breeding sites must be proofed against these: placement of mosquito nets on doors and windows and periodic disinfection.
• Affected birds should be isolated until fully recovered as they can transmit the virus by biting others.
• Disinfect all facilities and implements.

Remember that birds that recover are immunized against the disease, but can act as asymptomatic carriers by continuing to shed the virus, which occurs for about a month.

Treatment:

There are no specific treatments for Avipoxviruses. Antibiotics may be helpful in controlling secondary infections, and vitamin A or its natural precursors may aid in the healing process. The use of immunostimulants and normalizers of the intestinal flora is also advisable . Topical applications of astringent solutions such as mercury – chromium at 1-3%, in alcohol at 70º , are useful in skin lesions . Physical removal of crusted skin lesions is not advised as they generally spread infection by releasing viral particles.

Vaccines

• The Chevipok vaccine can be used by pricking into the neck or using a brush by removing feathers from the pigeon’s leg.
• NOBILIS® PIVESPOX is a lyophilized active virus vaccine for the immunization of healthy pigeons against diphtheria pigeonpox.