Respiratory disease in backyard poultry

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1 Vet Times The website for the veterinary profession Respiratory disease in backyard poultry Author : Marie Kubiak Categories : Vets Date : May 28, 2012 Marie Kubiak discusses the many possible causes of this condition in chickens you should be aware of Summary Respiratory disease is a very common reason for presenting backyard poultry to practitioners. Many bacterial, viral or fungal infections, and a number of other pathologies, can cause respiratory symptoms. A good knowledge of likely causes is important to allow a targeted diagnostic approach. Key words chicken, backyard poultry, respiratory FOR most vets treating commercial and backyard chickens, respiratory disease is a familiar problem, with many possible causes. Common clinical signs leading to presentation include a swollen face, discharge from the eyes or nose, open beak breathing, increased respiratory rate or effort, subcutaneous emphysema, coughing and cyanosis of the comb and wattle. Secondary effects include lethargy, partial or complete anorexia, a fluffed-up appearance and reduced egg production. Typically, this will affect many or all of the birds within a flock. Various bacteria, viruses, parasites, fungi and irritant substances can cause these symptoms, and effective treatment first requires an accurate diagnosis. 1 / 7

2 A comprehensive history of the flock is essential. Most incidences of respiratory disease are associated with introducing new stock. However, this does not necessarily mean the new birds introduced a disease, as the stress associated with mixing birds can cause recrudescence of an existing occult infection in the established flock. Clinical examination After a careful visual examination, prior to handling, a complete physical examination should be performed. For birds demonstrating severe dyspnoea, particularly open-mouth breathing or a hyperextended neck, it is prudent to administer oxygen therapy in a warm, quiet environment prior to examination. Where a group is affected, it is beneficial to examine more than one bird. Key factors to assess on examination are body condition, mucous membrane and appendage colour, evidence of ascites, checking for presence of oral lesions, glottis appearance and movement ( Figure 1 ), presence of emphysema ( Figure 2 ) and respiratory system auscultation. Cyanosis of the comb and wattle and a constantly dilated larynx carry a more guarded prognosis, as severe respiratory or gas exchange capacity compromise exists. Based on clinical findings, some differentials can be eliminated and a plan for further investigation can be created to identify specific pathogens or factors responsible. Bacterial causes Bacterial tracheitis, airsacculitis and pneumonia have all been documented in chickens. Opportunistic infections can occur in debilitated or immunocompromised chickens, but most bacterial infections are due to true pathogens. Mycoplasma are commonly isolated as a cause of bacterial respiratory disease in backyard poultry, although commensal species exist. Two particularly important species exist in chickens: Mycoplasma synovium and M gallisepticum. M synovium typically causes arthritis and very mild respiratory disease, and M gallisepticum causes respiratory and reproductive disease. Birds can be infected at any age (even as eggs), although young, stressed or ill birds are more susceptible. Spread occurs by close contact with other infected birds. Once infected, a bird remains infected chronically, even for life, so remains a risk to other birds and can have disease relapses if the immune system is compromised by stress or concurrent infection. M gallisepticum has a very typical appearance with upper respiratory symptoms, a clear nasal discharge, occasional sneezing and, very commonly, sinusitis ( Figure 3 ). As birds have an extensive infraorbital sinus surrounding the eye, the sinusitis and associated fluid accumulation is clearly seen as periocular swelling. Paralysis of respiratory epithelial cilia, due to local toxin production, can lead to opportunistic secondary infections and a more severe clinical 2 / 7

3 appearance, with airsacculitis and eventual septicaemia in advanced cases. Culture and speciation of bacteria from clinical cases is the gold standard for diagnosis, but Mycoplasma are a very fragile, thin-walled bacteria with poor survival outside the host. If samples are submitted for culture, then enriched swabs, post-collection chilling and rapid transport are essential. Polymerase chain reaction (PCR) techniques from choanal swabs are possible, but are not necessarily species-specific, and non-pathogenic species may be detected that lead to false positives. Serology is a very useful tool to assess antibody titres, but its use is limited where the vaccine status of birds is unknown. Treatment will reduce clinical signs, but may not clear the infection. Fluoroquinolones are mycoplasmacidal, but should not be used in birds producing eggs for consumption. Alternatives include soluble tylosin, which currently advises no egg withdrawal requirement following treatment. As mycoplasma is a recurrent problem once established in a flock, prevention is the best way to avoid problems. Eye drop and injectable vaccines are available, and measures to prevent wild bird contact are important in free-range birds. New birds should be quarantined and mycoplasma testing of unvaccinated birds considered before introduction into a flock. Other bacterial causes are much less common. Ornithobacterium rhinotracheale can cause a rapidly progressive upper and lower respiratory infection, often accompanied by arthritis, and demonstrates multi-drug resistance, so culture is necessary for appropriate therapy. Pasteurella multocida causes a rapid lower respiratory infection, with sudden death frequently noted in individuals. Viral causes Infectious bronchitis (IB) is a coronavirus with worldwide distribution that causes morbidity and mortality in galliformes particularly chickens. Many serotypes exist and pathogenicity varies dramatically. The virus is spread in respiratory, intestinal and renal secretions and, after a 24-hour incubation period, sneezing, nasal discharge, marked egg drop and general debilitation are noted. Adult birds with uncomplicated infection often recover within seven to 10 days, but secondary bacterial involvement or infections in juveniles can lead to significant mortality. As the virus damages cilia motility and epithelial integrity, opportunistic pathogens, such as Escherichia coli, can invade and cause more severe pathology. Death results from large caseous plugs of mucus obstructing the bronchi or trachea, or a secondary bacterial septicaemia. Concurrent mycoplasma infection leads to pathogen synergy and a dramatic increase in mortality. Some serotypes appear to have predilection for renal tissue, leading to increased and delayed mortality. Recommended diagnostic techniques include virus isolation in embryonated eggs, culture in tracheal ring preparations, PCR and serology. 3 / 7

4 In practice, clinical appearance combined with either PCR or serology are usually most practical. As with all serology, paired samples are preferable, but often treatment cannot be delayed until paired titres have been tested, so preliminary treatment must often be initiated based on significantly elevated single titres. No specific treatment is available, but prophylactic antibiotic therapy is strongly recommended to prevent secondary infection. Severely affected birds may need oxygen therapy, tracheal aspiration and supportive care. Vaccines are highly effective in prevention when administered correctly, and a live primer vaccine can be given from one day of age (though this is often given from three weeks of age for layers), with inactivated vaccine used subsequently for boosting immunity. It is important to vaccinate properly with a live strain, as IB is highly mutagenic and incomplete vaccination leads to potential progressive mutation and reversion to virulence as it passes through missed birds. Infectious laryngotracheitis (ILT) is a herpesvirus capable of latent state in the bird. Spread is horizontal in respiratory secretions and is usually slow through a flock, taking several weeks to affect all birds, unlike infectious bronchitis, which spreads through a flock within a few days. Dyspnoea with a highly productive cough results with ILT infection. Mucus and blood may be noted on the housing walls due to the violent nature of clearance in some cases. Mortality is frequently high and can reach 80 per cent. The virus persists in infected hosts with intermittent shedding, and is also stable for several weeks in the environment. Epidemiology is a key factor in diagnosing this condition with slow spread characteristic. Coughing up blood is pathognomonic in chickens. Tracheal histology is useful in the early stages, when inclusion bodies are widespread and PCR is more reliable in later disease. Serology is inconsistent. Although supportive care is possible for pet birds, antiviral therapies have not been validated and culling should be advised as birds remain a permanent risk to others. Vaccination should be considered in high-risk flocks, but is best avoided where no problem exists as live vaccines induce a latent infection and intermittent shedding of attenuated viral strains. Avian metapneumovirus (also known as turkey rhinotracheitis virus) is a cause of severe respiratory disease with up to 100 per cent mortality in turkeys. It is generally a lesser pathogen in chickens, with selflimiting oculonasal discharge and reduced production, activity and appetite noted. In chickens it infrequently develops to swollen head syndrome, with severe facial oedema and death ( Figure 4 ). This syndrome is believed to be due to secondary bacterial infection typically E coli and is never seen without concurrent metapneumovirus infection. However, avian influenza can present similarly and should be considered as a differential. PCR techniques are recommended for diagnosis and no specific treatment is possible. Vaccination is rarely justified in chickens. 4 / 7

5 Newcastle disease is caused by avian paramyxovirus-1 and is a notifiable and potentially zoonotic disease. Intestinal, respiratory and neurological symptoms may occur together or separately, with highly variable mortality dependent on strain characteristics. Mild respiratory symptoms may be seen alone with lentogenic or mesogenic strains, or in combination with nervous signs in neurotropic velogenic strains. A dramatic egg drop may also be noted with any form of the disease. No symptoms are pathognomonic, but combined neurological and respiratory disease or tracheal haemorrhage, airsacculitis and visceral haemorrhage on postmortem are indicative, and in suspected cases, advice should be sought from DEFRA. Fungal infection Respiratory aspergillosis is unusual in poultry, but should be a differential in any case of obstructive tracheal disease, air sac lesions or acute pneumonia. Endoscopy is recommended to evaluate potential lesions and debulking of fungal granulomas, plus systemic antifungal medication, is essential for treatment. No appropriate antifungal medications are licensed for use in poultry or other foodproducing animals, so treated animals should never be used for egg or meat production and owners should sign to agree to this condition should they choose to treat the chicken. Parasitic causes Syngamus trachea and cyathostomes are relatively common in free-range and backyard poultry, especially those in close proximity to wild corvids. Eggs are coughed up from the respiratory tract, swallowed and passed out in faeces. Under optimum warm conditions, the eggs take a week to develop to the infective larval stage within their eggs, but in cold conditions they may take several weeks to mature. S trachea can have a direct life cycle or utilise a paratenic host usually earthworms. The use of a paratenic host complicates elimination of this parasite from land as larvae can overwinter and are shown to persist for periods of more than three years within the earthworms. Other invertebrates, including slugs, beetles and ants, are also believed to be able to act as hosts. Ingested larvae hatch in the intestines and move via the bloodstream to the lung tissue, from which they migrate to the trachea. Cyathostomes require an intermediate host, but are otherwise similar in their transmission. Migration of large numbers of larvae through pulmonary tissue can lead to acute pneumonia and sudden death. Tracheal obstruction following infection is more common and presents with a gasping, outstretched neck, head shaking and anorexia. Older birds, or those with low levels of exposure, may be asymptomatic or develop an intermittent cough. Occasionally cyathostome egg inhalation can lead to aspiration pneumonia, but this is not seen with S trachea. 5 / 7

6 Diagnosis is by clinical signs, presence of worms within the trachea or identification of the nematode eggs in a faecal sample. S trachea has a distinctive bioperculate, thick-walled egg of greater than 80µm in length, whereas cyathostomes have a single operculum. Capillaria species are primarily intestinal parasites, but can cause fibrinonecrotic plaque formation in the pharynx, which may interfere with respiration. Cytology of plaques or faecal examination will show small, thin-walled bioperculate eggs (less than 60µm in length). Flubendazole (Flubenvet, Elanco Animal Health) is licensed for nematode treatment in poultry, including Syngamus and Capillaria species, and has a zero egg withdrawal period, so in the author s opinion, is the most appropriate agent for treatment. Non-infectious causes Environmental irritants can lead to respiratory distress. Ammonia build up, due to poor hygiene, leads to tracheal epithelial damage and, together with overcrowding, stress, poor ventilation and dietary inadequacies, can predispose to infectious respiratory disease. Smoke inhalation and various chemical sprays can also lead to respiratory symptoms and removal from contaminated areas should be carried out with oxygen therapy, as required. Smoke inhalation can lead to pulmonary oedema with diuretics, and covering antibiotics are necessary in severe cases. Steroid administration should be avoided unless critical due to avian sensitivity to immunosuppressive effects of corticosteroids and increased risk of secondary bacterial or fungal infection as a result. Ascites can present with respiratory signs due to respiratory tract compression and oedema, exacerbated by the lack of a diaphragm in birds. A distended coelom is clearly evident on examination and merits further investigation to determine the cause ( Figure 5 ). Many cases result from reproductive disease, such as egg peritonitis, but hepatopathy and congestive heart failure are differential diagnoses. Respiratory disease is very common in chickens and second only to egg-related conditions as the cause for presentation at the author s clinic. Many of the causes can be avoided by vaccination strategies, although owners are often reluctant to vaccinate as commercial vaccines come in large vials of several thousand doses and must be disposed of within hours of opening. However, these vaccine vials are not prohibitively expensive and encouraging flock owners or poultry clubs to group together to avoid waste leads to a very inexpensive way to protect their birds against disease. 6 / 7

7 Powered by TCPDF ( Biosecurity is also a major problem most smallholders will obtain birds from various sources intermittently, have no knowledge of seller flock health problems or vaccination strategies and introduce them immediately into an existing flock. Many poultry hobbyists also regularly show their birds. At shows birds might remain caged for up to three days in the proximity of other birds, with a high risk of disease transfer. These owners must be educated in disease prevention, including vaccination strategies and quarantine protocol. A closed flock is ideal, but should new birds need to be introduced, or existing birds mixed externally for any reason, then a prolonged quarantine period of an absolute minimum of one month in a completely separate enclosure with no possibility of airborne transfer between birds is essential. 7 / 7

MYCOPLASMOSIS - A SERIOUS PROBLEM OF POULTRY INDUSTRY

By, Dr. J. L. Vegad Advisor Phoenix Group MYCOPLASMOSIS - A SERIOUS PROBLEM OF POULTRY INDUSTRY Mycoplasmosis, commonly known as chronic respiratory disease of chickens, has existed in our country since