Managing fleas and mites (Proceedings)

Fleas

Fleas are still the most common cause for parasite induced pruritic skin problems in many geographical regions. Since the nineteen's many different drugs and preventative have been introduced to prevent and to treat flea infestation, and certainly the occurrence of severe widespread infestations have declined. However, the lack of pet owner compliance and neglect of addressing environmental flea ainfestation are probably the most common causes for a chronic recurring flea problem. Once a home is infested, control is often difficult, time-consuming and expensive, and so a lot of emphasis should be concentrated to prevention. Successful eradication of a flea infestation requires knowing the specifics of the flea life cycle and the mechanisms and efficacy of available flea preventatives. Although concern has been raised of fleas developing resistance to some of the commonly used topical flea preventatives (e.g. Frontline), these reports are rather anecdotal and have not been confirmed by controlled studies so far. At this point we have to consider that the "appearance of flea resistance" is more likely due to lack of compliance and knowledge about the flea life cycle, as well as unrealistic expectations from the flea product dispensed by veterinarians.

Flea biology

The flea life cycle of Ctenocephalides felis felis consists of 4 main stages and is completed between 21-174 days. Most adult fleas live on animals, but adult fleas make only ~5% of the entire flea population, whereas the rest (eggs, larvae and pupae) live in the pet's environment. Female fleas start to produce eggs, approximately 24 hours after their first blood meal. Adult fleas can survive up to 100 days and produce 40-50 eggs per day! Flea eggs usually fall of the animal and will hatch within 2-10 days. The larval stage is the most sensitive stage and less than 25% will survive. Heat, cold, dryness and limited food supply (organic debris) is the limiting factor for the survival of the larval stage. For this reason the larvae seek protection by crawling (up to 40cm) into deeper areas of the carpet, underneath furniture, etc. After two molts the third larval stage enters the pupal stage. The pupa is resistant to desiccation and temperatures of >3°C and <35°C. The flea remains in the pupal stage 5 to 140 days depending on the environmental condition (ideal: 27°C, 80% humidity, mechanical pressure, vibration). If the environmental conditions are ideal, it is not unusual that many fleas will emerge from the pupal stage at once and cause a sudden outbreak.

For indoor only pets a flea growth inhibitor may be enough as a preventative. However, pets with outdoor exposure are more likely to get in contact with fleas. In these animals a preventative with a fast-acting adulticide will interrupt the flea life cycle before the flea has a chance to establish indoor. Urban wildlife such as opossum, raccoon, coyote, fox and feral cats are important carriers of fleas and potential source for infesting a pet owner's yard. Removing and/or limiting access to areas such as crawl spaces, dark areas under decks, garage, door mats, cat and dog food put outside, moist dark areas under shrubs and piles of leaf and limb will help to minimize the areas for fleas to establish.

Flea preventatives

Flea allergic dermatitis or flea bite hypersensitivity is commonly present in atopic patients, and so effective and strict monthly flea prevention is strongly recommended. Because owners often don't see the fleas on their pets and don't understand the concept of flea allergic dermatitis they are often arguing about the sense of a strict flea prevention protocol. It is important to make the owner understand that current flea preventatives don't have an effective flea repellent effect, and that even the use of fast-acting adulticides (e.g. Comfortis) may not completely prevent the flea from biting the pet and cause irritation. Scientists have shown that once a flea gets in contact with a pet, biting and feeding occurs within few minutes. Despite this deficiency, the use of a fast-acting adulticides will reduce pruritus due to the faster reduction of the flea burden in the pet's environment.

Don't forget that all pets in the household should be treated at the same time. If a flea infestation has established in the pet's environment topical or oral flea preventatives alone will not be able to eliminate the problem immediately. In fact it can take several months until the flea population starts to decrease. For this reason a combination of flea prevention and environmental control and treatment should be initiated to achieve a successful and quick elimination of the flea problem.

Mites

Ectoparasites are common and distributed worldwide. Most of them cause pruritus which results in self-trauma and secondary problems such as pyoderma. Many of these ectoparasitic diseases are contagious, zoonotic and so a public health concern. Based on their dermatological implication the 5 following parasites will be discussed: Demodex spp., Sarcoptes scabiei, Cheyletiella spp., Otodectes cynotis, and lice.

Demodicosis

Causes inflammatory skin disease due to larger than normal numbers of mites within hair follicles. Genetic predisposition and immuno-compromised animals seem to be an important factor in the development of generalized disease. In dogs 3 different species (D. canis, D. injai, and an unnamed short-bodied mite) and in cats 2 different species (D. cati and D. gatoi) are known.

In dogs we differentiate between juvenile- and adult-onset demodicosis. Demodicosis is considered a non-contagious disease, except for D. gatoi.

Clinical signs are variable and may range from a non-pruritic localized area of alopecia to generalized severe pruritic dermatitis with extensive alopecia and crusting. In the pruritic patient secondary pyoderma is commonly present.

Diagnostic test of choice are multiple skin scrapes, which should be repeated during treatment at least once monthly until complete cure has been achieved.

Treatments considered effective for generalized cases are:

     - Ivermectin: 0.2-0.6mg/kg PO every 24 hours (cure rate up to 90%)

     - Milbemycin oxime: 0.5-2mg/kg PO every 24 hours (cure rate up to 90%)

     - Doramectin: 0.2-0.6 mg/kg SC once weekly (cure rate ~85%)

     - Amitraz: whole body dips with 0.03-0.05% amitraz solution once weekly (cure rate up to 86%)

     - Topical moxidectin (Advantage Multi): applied topically once weekly (cure rate ??%)

If D. gatoi has been identified all in contact cats should be treated with 2-4% lime sulfur dips every 3-7 days for 4-8 weeks. A treatment alternative in cats could be 0.2-0.6mg/kg SC once weekly.

One of the most common causes of treatment failure is premature treatment discontinuation!

Scabies

Intensely pruritic and contagious disease. Sources of infection are: animal shelter, contact with stray dogs or wildlife, grooming or boarding facility. Diagnosis must be based on history, clinical presentation, presence of pinnal-pedal reflex, response to scabicidal treatment, because skin scrapings are often negative.

If scabies is suspected treat all in-contact animals:

     - Selamectin (Revolution): 6-12mg/kg topical every 14 days for at least 4 times

     - Ivermectin: 0.3mg/kg PO every 7 days or SC every 14 days for 4-6 weeks

     - Doramectin: 0.2-0.6mg/kg SC every 7 days for 4-6 weeks

     - Moxidectin (Advantage Multi): apply topically every 14 days for at least 3 treatments

     - Lime sulfur 2-3% dips: whole body dip once weekly for 4-6 treatments

     - Amitraz 0.025-0.03% dips: apply every 14 days for 3 treatments

     - Fipronil spray: apply 3ml/kg to the entire body every 14 days for 3 treatments

Cheyletiellosis

Uncommon variable pruritic disease which is contagious and can affect different animal species (is considered the number one ectoparasite in rabbits). Asymptomatic carrier may be present. Excessive seborrhea especially over the dorsum is a common finding.

Mites, larvae or eggs may be found on superficial skin scrapings, acetate tape imprints, or material obtained from flea-combed hairs.

All animals in the household should be treated once weekly for at least 6-8 weeks

     - Selamectin (Revolution): 6-15mg/kg topical every 14 days for at least 4-6 weeks

     - Ivermectin: 0.3mg/kg PO every 7 days or SC every 14 days for 4-6 weeks

     - Doramectin: 0.2-0.6mg/kg SC every 7 days for 4-6 weeks

     - Moxidectin (Advantage Multi): apply topically every 14 days for at least 3 treatments

     - Lime sulfur 2-3% dips: whole body dip once weekly for 4-6 treatments

     - Fipronil spray: apply 3ml/kg to the entire body every 14 days for 3 treatments

Ear mites

This psoroptic mite most commonly affects kittens. Adult cats are often asymptomatic carriers. The condition is often intensely pruritic with dark-brown crumbly to purulent (indication for secondary bacterial infection) discharge. Diagnosis is made by otoscopic exam and ear smears.

Before medication is applied to the ears, thorough ear cleaning should be performed in house. In-contact animals should be treated as well. Effective treatments currently used:

     - Milbemycin solution (Milbemite) instilled into each ear once

     - Ivermectin topical solution (Acarex) instilled into each ear once

     - Neomycin-thiabendazole-dexamethasone (Tresaderm): 0.125-0.25ml every 12 hours for 2-3 weeks

     - Gentamicin-clotrimazole-mometasone (Mometomax): 0.25-0.5ml every 12 hours

     - Fipronil 10%: 2 drops into each ear twice 2-4 weeks apart

     - Selamectin: 6-12mg/kg every 2-4 weeks for 4-8 weeks