Dacryocystitis – Rabbit

Description

Dacryocystitis is one of the most common conditions encountered in practice and can be one of the most difficult to treat due to the persistence of the organism involved and the tendency of the condition to recur. It is very important to examine the teeth and both nasolacrimal ducts of every rabbit irrespective of the reason for which the animal is presented for clinical examination.

Clinical Signs

Clinical signs of dacryocystitis include a milky discolouration of the precorneal tear film, epiphora, crust formation along the affected eyelid margins and a caseous discharge from the nostril. The condition can be unilateral or bilateral. The clinician may have to apply digital pressure on the lacrimal sac to observe a milky discharge from the lacrimal punctum. Keratitis and conjunctivitis are sometimes observed. A white crust on medial canthus is a frequent early clinical sign.

Aetiology

The prime agent of aetiological significance is dental malocclusion. The constant growth of the teeth combined with the low bone density of the rabbit skull results in the migration of the roots of the teeth leading to:

1. Occlusion of the naso-lacrimal duct by the roots of the incisors (welling of the milky discharge up the lacrimal apparatus results in epiphora).
2. Invasion of the eye socket by the roots of the molars leading to retrobulbar infection, buphthalmos or simply ocular irritation and epiphora.

Microbiological investigation yields profuse growth of many organisms, usually Pasteurella multocida (Petersen-Jones and Carrington 1988), but Staphylococcus species and Streptococcus species, can also be frequently involved. Dacryocystitis can be due to an ascending infection from the nasal cavity via the nasolacrimal duct and is a constituent part of the syndrome of Pasteurella infection in rabbits (Whittaker 1989).

A survey conducted by Leo Laboratories in 1994 yielded:

1. Staphyloccus spp. - non-haemolytic, 17 isolates; haemolytic coagulase -ve, 10 isolates; haemolytic coagulase +ve, 5 isolates.

1. Streptococcus spp. - non-haemolytic, 4 isolates; alpha-haemolytic, 2 isolates

1. Pasteurella spp. - Pasteurella aerogenes 2 isolates, Pasteurella multocida 3 isolates, unidentified Pasteurella spp. 2 isolates,

1. Bacillus spp. - 7 isolates,

1. Corynebacterium spp. - 5 isolates,

1. Enterobacter spp. - 3 isolates

1. E coli - (non-haemolytic) 3 isolates

1. Pseudomonas spp. - Pseudomonas vesicularis 2 isolates, unidentified Pseudomonas spp. 1 isolate,

1. Branhamella spp. - one isolate

1. Proteus spp. - one isolate

1. Acinetobacter junii - one isolate

1. No isolates were detected in 12 specimens.

As well as dental disorders, a triggering factor for the establishment and persistence of infection is thought to be the ammonia produced either by the degenera­tion of urinary urea in a poorly absorptive litter (Okerman 1988) or from a pet maintained on an imbalanced (high protein) diet (Jenkins 1991). I always counsel the owners of affected animals to attend to hygiene and diet simultaneously. Peat moss /Turf mould is recommended as hutch litter due to its ability to absorb the ammonia produced by the decomposition of urinary urea.

Treatment

The condition is very difficult to treat as tooth roots are an important factor in the persistent eye infections of rabbits and the distal naso-lacrimal duct may become involved with periapical abscessation of the maxillary incisors (overlong incisor root with thinning or periosteal proliferation of the palatial bone). Dental conditions do not, generally speaking, resolve quickly in rabbits, if at all. Also the causative organism, particularly if it is the ubiquitous Pasteurella multocida, seems to be well adapted to the conjunctival microclimate and local immunity appears to be suppressed. In addition, cannulation of the entire course of the lacrimal duct is impossible due to the tortuous course and varying diameter of the duct although flushing from the lacrimal punctum is possible (Burling et al 1991). Even if the condition is discovered only co-incidentally when the rabbit is presented for some other reason, the following approach should be undertaken:

• Make sure that the dental disease is thoroughly addressed.

• Under local analgesia using proxymetacaine hydrochloride BP 0.5% (Minims; Alcon), I canulate the lacrimal duct as described by Petersen-Jones and Carrington (1988) and flush the apparatus (irrigating canula reference AS85 from Arnolds Veterinary Products, or iv cannula) with sterile saline until the fluid runs clear from the the nares. The bevelled end of the Surflo intravenous canula makes it an easier instrument for this purpose. The apparatus is then irrigated diluted ophthalmic preparations of antibiotics, ideally following microbial cultures and sensitivity testing.

• In some cases it is impossible to effect drainage of the tenacious purulent material. I once had success with a solution of trypsin is infused into the duct and the procedure is reattempted after twenty-four to forty-eight hours.

• Follow-up treatment comprises systemic and topical antibiosis, usually with oxytetracyline (Engemycin® 5%; Intervet) and tetracycline ophthalmic ointment (Fucithalmic®; Leo) or gentamicin (Tiacil®; Virbac) applied to the conjunctival fornix q 6-8 hrs, or antibiotics are select­ed after sensitivity testing. In the absence of antibiotic sensitivi­ties. I have noticed that topical applications of ophthalmic preparations containing neomycin are frequently not effective in the treatment of this condition.

Prognosis

Prognosis the favourability of the prognosis is inversely proportional to the dental health and to the length of time taken for any response to treatment. Poor response is an indication for withdrawal of treatment and microbiological investigation, including antibiotic sensitivity testing. Long-term, repeated irrigation may result in permanent stenosis or obstruction.

In young animals in a collective situation (eg. pet shops) a simple conjunctivitis in which the teeth are not involved may be encountered. Cytology may be useful in identifying the causative organism(s). Chlamydophila psittaci may be involved (scrapings from the back of the membrana nictitans may be helpful) and should respond to ciporofloxacin eye drops (Ciloxan®; Alcon Labs).