Allergic reactions to insect bites are not unique to cats and occur in all species of mammals. Reactions to insect bites have been commonly reported with mosquitoes, ants, spiders, bees and wasps.
Where there is a history of exposure to mosquitoes, as occurs near water (rivers, lakes, swamps) or if there are water containing vessels surrounding the habitat where the cat resides, then allergic reactions are likely to occur. Generally cats are insensitive to mosquitoes and considerable numbers are required to evoke allergic responses.
Mosquito-bite hypersensitivity is an atypical form of eosinophilic granuloma complex, and the hypersensitivity to mosquito saliva triggers localised reactions characterised by papular, erosive, crusting and depigmentating eruptions on the nose and pinnae. Immunoglobulin E appears to be the predominate antibody responsible in this unique allergic response in cats.Mosquito bite hypersensitivity in cats is triggered by a type I hypersensitivity reaction to mosquito saliva antigens. Certain other factors may be involved in the formation of delayed papular reactions, including presence of other secondary parasites such as filarids and their associated bacteria.
Typical clinical features are seasonal (summer) and cats show symmetric dermatitis primarily on the pinnae (ears), planum nasale and bridge of the nose. Peripheral lymphadenopathy and moderate fever associated with blood eosinophilia are commonly seen. No age, breed or coat color predisposition has been noted. Allergic reactions occur with most species of Anopheles spp and Culicoides spp mosquitoes. Some cats also show wheals on chest, pads and tail/rump region within 20 minutes of mosquito exposure.
Other clinical forms, indolent ulcers, oral granulomas, cutaneous plaques and eosinophilic keratitis due to mosquito bites are seen, in the absence of typical papular and scaling lesions on the ears and distal limbs. These lesions regress when the cat is kept in a moquito-free environment.
Aside from causing hair loss and irritation to the sensitive skin of the area, reactions to flea bites are relatively innocuous. However, the likelihood of infection from mosquitoes with Dirofilaria immitis or Dipetalonema reconditum have been recorded and are a cause of sudden death in adult cats.
Differential diagnoses would include flea allergy dermatitis, food allergy dermatitis, atopy, drug reactions, pemphigus foliaceous lupus erythematosus, actinic (U-V) dermatitis and squamous cell carcinoma.
Avoiding cat exposures to mosquitoes during prevalent times when mosquitoes feed (dawn and dusk) and prudent use of insect repellents/lotions may help alleviate clinical symptoms. The judicious use of Heartworm preventative medication is warranted in mosquito areas to prevent secondary infection of cats with Heartworm disease.
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