Sinusitis is the inflammation of the infraorbital sinuses (essentially a sinus infection). The infraorbital sinus interconnects with the nasal cavity and porous calvaria. This interconnection of facial elements is why when any inflammatory reaction in the sinus or nasal passages occurs, it involves most of the anatomic structures of the chicken's head; this is why sinus infections in chickens are often difficult to diagnosis and treat. Any incidences of upper respiratory tract disease in chickens can result in an accumulation of pus and cellular debris in the infraorbital sinus, often leading to conjunctivitis.
The following diseases can cause sinusitis in chickens:
- Chronic respiratory disease (CRD): Chronic respiratory disease (CRD), also known collectively as mycoplasma gallisepticum (MG) infection, is considered to be one of the major pathogens that cause respiratory disease in poultry. It tends to develop slowly in flocks and associated with progressive and chronic respiratory signs. Chickens with chronic respiratory disease often show clinical signs associated with the respiratory system, which include mild tracheitis, sinusitis, airsacculitis and conjunctivitis.
- Infectious Coryza: Infectious coryza is an acute upper respiratory disease of chickens, caused by Avibacterium spp. It is most often transmitted to flocks by introduction of a new chicken or reintroduction of existing flock member that recently attended an event which included other poultry.
- Infectious laryngotracheitis: Infectious Laryngotracheitis (ILT) is an acute respiratory tract infection of chickens, caused by the Laryngotracheitis Virus (LTV). LTV strains vary in virulence from highly virulent strains that is highly infectious and usually fatal to low virulent strains that cause mild to inapparent infections. The two historically most common presentations of ILT are classified as two forms--mild epizootic and severe epizootic.
- Swollen head syndrome: Swollen head syndrome (SHS) is an acute, highly contagious upper respiratory tract infection of poultry. SHS is caused by infection with the avian metapneumovirus (AMPV), a type of pneumovirus which is classified into four subtypes (A, B, C, and D). The typical clinical signs seen in chickens infected with the virus include swelling of the periorbital and infraorbital sinuses, particularly around the eye, coupled with mild conjunctivitis.
- Avian Influenza: Avian influenza (AI) is a highly contagious reportable disease of poultry that is sporadically seen in backyard flocks. AI is caused by infection with type A influenza virus, which is a type of orthomyxovirus of the family Orthmyxoviridae. Clinical forms of AI range widely from low pathogenic (LPAI) to highly pathogenic (HPAI). Clinical signs can vary from a mild infection (chickens show loss of appetite, deceased egg production, mild respiratory disease, and diarrhea) for LPAI to severe respiratory, neurological, and gastrointestinal (GI) signs with HPAI (resulting in high mortality rates).
- Fowl cholera (FC): Fowl cholera, also referred to as avian pasteurellosis, is a contagious bacterial disease caused by Pasteurella multocida and affects domesticated and wild birds worldwide. FC usually appears as an acute, septicemic disease but it can also occur as a chronic disease. Mature chickens are more susceptible than young ones, and turkeys are more susceptible than chickens. Chickens less than 16 weeks of age generally are quite resistant.
With severe chronic sinusitis, the accumulation of mucus and pus turns into caseous necrotic debris, which becomes so bulging that the increased pressure causes damage to the nares, nasal conchae, operculum, and nasal cavity of the chicken. In addition, with chronic sinusitis, chickens are at an increased risk of developing whats referred to as a 'sunken eye', in which the globe of eye retreats into its socket. This gives the appearance of the chicken 'losing it's eye', and usually just involves one eye, but it can occur in both eyes.