94 (68)

A Practical Guide to Feline Detmatology

ducibility in both diagnosis and treatment ^23,24.

Some Ctenocephalides felis felis antigen fractions have now been produced by genetic engineering^19,a. These reagents may allow development of better diagnostic tools offering enhanced reproducibility, especially in vitro but also in vivo^23,2S.

Intradermal testing

Intradermal testing kits contain non-standardised whole body extracts of Ctenocephalides felis felis, ready to use at a concentration of 0.1% W/V. The protocol for using flea extract is exactly the same as for the aeroallergens. Reactions are read at 15-20 minutes and 48 hours after administration. At 20 minutes, any clearly erythematous reaction with a diameter greater than the average of the positive (histaminę) and negative (diluent) Controls is considered positive (Fig. 9 : 16). If the reaction around the injection site of the flea extract is “negative” at 20 minutes, it is re-examined at 48 hours. At that time, the presence of just a palpable swelling can be interpreted as a positive result. In practice, intradermal testing in the cat is often hard, even impossible, to interpret. Furthermore, in the absence of studies comparing normal animals with those with FAD, the diagnostic value of this test is unknown. Most reactions are seen at 20 minutes, those at 48 hours seem much rarer⁴'⁶.

Laboratory tests

No serological test has to datę been validated for use in the cat⁵. With regard to FAD diagnosis, two approaches are promising: the in vitro basophil degranulation test and serological tests using an alpha recombinant chain of the human FceRI receptor. However, the incidence of sensitisation in normal cats is so great that the positive predictive value of this test is very poor²⁶.

Allergy testing in the cat is, therefore, very unrewarding. A positive allergy test does not confirm FAD. Eąually, a negative test does not rule it out⁶.

Treatment

Treatment is based mostly on flea control for the affected cat, in-contact animals and the environment. Efficacy relies on the owner having a good understanding of the flea control programme. The life cycle and flea habits must be carefully explained to the owner along with the circumstances in which FAD appears (i.e. injection of flea saliva into the skin).

Antipruritic treatment is often necessary to give immediate relief to the cat (and the ownersl). It may be need-ed for long periods in cats which have marked pruritus despite well-conducted flea control.

Short-acting corticosteroids (prednisone, prednisolone or dexamethasone) can be given at usual anti-inflam-matory doses. They produce few side-effects when given over a short period. Cats with severe pruritus must be treated with dexamethasone, often morę effective but associated with morę rapid onset of side-effects. When pruritus has sufficiently subsided, prednisone or prednisolone should again be prescribed at a dose of 0.25-0,5 mg/kg BID. For prolonged use, orał, alternate-day, corticosteroid therapy, is preferable to parenteral administration, despite being harder to administer to some cats.

Antihistamines are sometimes useful. Chlorpheniramine (0.5-1 mg/kg BID) and hydroxyzine (2 mg/kg BID) are most commonly used in the cat. Several weeks treatment may be needed to achieve a satisfactory response and the concomitant use of corticosteroids during the first few weeks is therefore desirable²⁷.

Synthetic progestagens (e.g. megoestrol acetate) are no longer in vogue given their severe side-effects: pyome-tra, diabetes mellitus, gynecomastia, mammary hyperplasia or adenocarcinoma, polyuria and polydipsia, obe-sity, behavioural changes and increased arterial pressure.

Immunotherapy using whole body extracts of Ctenocephalides felis felis is not effective ²⁸. This could be due largely to the poor allergenic ąuality of whole body extracts. Trials with purified fractions or recombinant anti-gens could, in futurę, offer new treatment opportunities.