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"Common Signs are Common"
Diagnosing respiratory problems in poultry

DAHS Technical News Bulletin, 16 July 2009

In this short technical news bulletin, Stephen Lister talks about the respiratory problems in poultry.

Respiratory disease is not uncommon in poultry production and can be associated with significant clinical signs and morbidity. The exact nature of the clinical signs and the level of subsequent mortality can be determined by a variety of factors. These include the agent or agents involved, or the combination of infectious challenges experienced, all of which can be significantly modified by environmental effects. Infectious agents involved include viruses, mycoplasmas, and primary or secondary bacterial challenge.

Most respiratory signs in poultry tend to be non-specific. This, and the frequent occurrence of multiple agent challenges, can make specific diagnosis of the involvement of particular disease agents very difficult.

Confirmatory diagnosis can therefore require a combination of techniques. These include local knowledge of disease problems on other farms in the locality, knowledge of the disease status of any supplying breeder flocks within the integration, together with detailed veterinary involvement using clinical examination, post mortem examination and subsequent laboratory tests.

The current concerns relating to highly pathogenic H5N1 avian influenza infection on a global basis mean that all producers should be keen to diagnose any suspicion of influenza infection without delay. Prompt identification of index cases of H5N1 infection in any significant poultry population and its rapid confirmation and stamping out is the cornerstone of effective control of this potentially devastating infection. As a result, producers are likely to be concerned with any significant or unusual clinical disease in their flocks at this time.

Suspicion of the presence of highly virulent avian influenza infection, or indeed Newcastle disease virus infection, in a poultry flock is most likely to result from high, rapid and unexplained mortality, or very severe drop in egg production. The severity of clinical signs can be significantly influenced by the strain or type of virus involved. Infection with highly virulent strains should be more straightforward. Affected flocks are likely to show a large number of depressed, sick and dying birds, where clinical respiratory signs may be difficult to detect due to rapid death. The likelihood of the presence of either of these viral diseases will be greatly influenced by their known presence in the vicinity of the affected flock, or known risk factors associated with likely introduction from a more distant source. Clinical respiratory signs when present tend to involve mouth breathing, runny eyes and nose, dark congested combs and wattles and variable degrees of sinus involvement and head swelling. Affected birds are likely to show a high fever. In addition, in the case of Newcastle disease infection there may be significant nervous signs of twisted necks, trembling or difficulty walking.

In relation to less severe, endemic diseases being dealt with by producers on a more regular day-to-day basis these are almost by definition able to be suspected by virtue of the less severe clinical signs observed and the basis of the fact that common things are common.

One of the most common respiratory infections of chickens is Infectious Bronchitis (IB) infection. With IB infection clinical signs of respiratory noise, runny eyes and nose and egg production drops can be sudden and severe, but differentiation from influenza or Newcastle disease infection would be related to the absence of significant acute mortality in uncomplicated IB infection.

In the case of mycoplasma infection, notably with Mycoplasma gallisepticum, severe sinusitis and head swelling can show rapid onset, frequently with high numbers of sick birds. Differentiation from influenza or Newcastle disease infection can usually be made on the basis of the absence of high acute mortality, and circumstantial evidence of mycoplasma in supplying breeding stock or possible horizontal spread from other affected flocks in the locality. However, without treatment, mortality with mycoplasma can rise significantly and rapid laboratory investigations and blood testing may be needed to confirm suspicions.

Other agents that may be associated with significant respiratory disease in commercial or backyard poultry include viruses such as avian pneumovirus (also known as TRT or SHS) and infectious laryngotracheitis (ILT), and bacteria such as Ornithobacter rhinotrachale (ORT) Haemophilus paragallinarum (fowl coryza), and Pasteurella multocida (fowl cholera). Such agents can be present in multiple infections in a flock, often complicated by secondary E coli infection.

The variety of agents which may be present, the non-specific nature of clinical signs of respiratory signs in affected flocks and understandable concern about the introduction of potentially devastating viral infections of avian influenza or Newcastle disease illustrate the need for prompt veterinary involvement, detailed clinical and post mortem examination and laboratory testing as appropriate in any case where disease is severe or of sudden onset.

Constant vigilance and frequent clinical examination of poultry flocks for signs of ill health are significant aspects of good stockmanship at all times. With the spectre of the presence, however remote, of virulent viral infections of avian influenza or Newcastle disease all producers should seek veterinary advice whenever they are concerned about the health of their birds. However, common things are common and producers should maintain effective well planned biosecurity programmes using disinfectants of proven efficacy, such as DuPont’s Virkon® S, and common sense procedures of disease control, in good times and bad!

 

Stephen Lister BSc BVetMed CertPMP MRCVS

 

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