Insect Bite Dermatitis
Insect bite dermatitis can be caused by various hematophagous insects due to the mediators or toxic products present in their saliva; it is sometimes associated with hypersensitivity reactions.
Cats are more commonly affected than dogs, perhaps because they roam more and because of their “lie and wait” way of hunting. Papules, erythema, erosion, and alopecia are seen mainly on the thickened tip of the pinna. The border and the dorsal side can also be affected. In dog breeds with pendulous or broken ears, lesions are seen on the surface of the pinna where the ear folds down. In severe cases, multiple small ulcers covered with hemorrhagic crusts are present.The causative insects vary with the season, environment, and climate.
The rabbit flea (Spilopsyllus cuniculi) can infest dogs and cats that are in contact with infected rabbits (pet, hutch, hunting). Transmission is reported to occur mainly at the time of rabbit parturition. This flea is found mainly in Europe and Australia. It stays tightly attached to its host’s skin, usually at the tip of the pinna, and should not be confused with a tick.
Mosquitoes (Aedes spp., Culex spp.), stable flies (Stomoxys calcitrans), and blackflies (Simulium spp.) may cause lesions on the pinna. The bridge of the nose and/or the periocular area can also be affected. Their presence is seasonal in endemic areas. Because they do not stay on their host, the diagnosis is often putative.
Differential diagnosis includes actinic dermatitis, trauma, canine eosinophilic pinnal folliculitis, and eosinophilic furunculosis of the face. Diagnosis is based on history and clinical signs. Lesions are often infiltrated with eosinophils and show secondary infection.
Treatment should be aimed at the lesions and at reinfestation prevention. Lesions are cleaned and topical antibiotics are applied. Steroids are often used because of the common hypersensitivity component of the disease. Steroids are not indicated if ulceration is present because they slow the healing process. Elimination of the animal’s exposure to the insects is the only effective prevention but is usually difficult to achieve. Measures include treatment of farmed or pet rabbits, prevention of free roaming, and application of a repellent. Permethrins and pyrethroids have good repellent activity, as shown with a deltamethrin-containing collar against phlebotomes, but they are toxic in cats. Vaseline mixed with citronella, DEET, or N,N-diethylmetatoluamide allows the product to stay longer on the ear tip.
More on the topic Insect Bite Dermatitis:
- Insect Bite Dermatitis
- Dermatoses of the Concave Pinna
- Allergic Dermatitis
- Streptobacillus moniliformis Infection: Rat Bite Fever
- Factors that Predispose the Ear to Otitis Externa
- Dermatoses of the Ear Margin
- EXAMPLES OF DISEASES CAUSED BY INSECTS, MITES, AND TICKS