Download canine itchy diseases

CANINE ITCHY DISEASES
Cesar Alvarez Yotti
Ctro Dermatológico Veterinario Skinpet
C/Nazaret 2 (Móstoles)
C/ Andrés Torrejón 18 (Madrid)
Parasitic diseases
Sarcoptic mange
It is a contagious parasitic skin disease caused by a mite called Sarcoptes scabiei variety canis, which
excavates galleries in the stratum corneum of dogs where the females lay their eggs .The signs appear 3
week after the contact with the parasite. It causes a very intense itching, 9-10 on the canine pruritus
scale, and self-trauma, accompanied by crusted lesions mainly in areas of low capillary density such as
ear margins, outer side of the elbows and sternal and groin regions.
The diagnosis is obtained after performing extensive multiple superficial scrapings of the areas preferred
by the parasite. Extensive skin scrapings with negative result do not rule out the disease, since a very
small number of mites is capable of producing very severe symptoms through a host hypersensitivity
mechanism against the mite. It is important to note that the Sarcoptes scabei variety canis doesn't
normally multiply on human skin. Therefore, the itching usually subsides when the source of infection is
treated.
Otodectic mange
It is also called ear mites, and is a skin disease caused by the multiplication of the mite Otodectes cynotis
in the ear canal. It can affect both the dog and the cat, though the latter is much more common, especially
in puppies less than six months of age. Otodectes feeds on earwax and cellular debris inside the ear,
where they complete their life cycle in 21 days, but sometimes can leave the ear to colonize other
neighboring areas, where they can live a few days. They cause a ceruminous otitis, resulting in abundant
brownish-black ooze secretion referred to in literature as "coffee grounds". Diagnosis is simple and is
performed by otic swabbing with a cotton swab and microscopic observation of the sample suspended in
mineral oil.
Demodicosis
Demodex canis occurs in dogs and is the most frequently identified mite. Demodex Injai variety is a much
less common cause of canine demodicosis. The disease develops due to a temporary or permanent
immunosuppression. Some of the most common predisposed breeds are: French and English bulldog,
Bullterrier, Pug and Shar Pei. The severity of the disease can be very variable, depending on its localized
or generalized extension and if accompanied by severe secondary infection in the pustular type. The
degree of pruritus is very variable, depending mainly on the extent of the disease, the host sensitivity and
the existence of secondary infection. The diagnosis is made by deep skin scrapings of the bald areas.
Cheyletiellosis
Mites from the Cheyiletiella family are large, visible even by the use of simple magnification systems, like
a magnifying glass. They affect different species such as dogs, cats, rabbits and humans. Cheyletiella
yasguri is typical of the canine species, and Cheyletiella blakei presents tropism for the feline species.
They mainly feed on scales and epidermal cellular debris to complete a cycle of 21 days. They cause a
severe scaly dermatosis, distributed along the trunk, and accompanied by itching of varying intensity. The
diagnosis is made by acetate tape applied on the affected skin surface, followed by direct microscopic
observation. In general, this method is very sensitive in dogs but not in cats because of their grooming
behavior and because a small number of mites may be often responsible for a very intense itching.
Trombiculosis
Seasonal disease (autumn and summer) caused by the pathogenic action of hexapoda mite larva of the
family of Trombiculidae. In Europe, the species is called Neotrombicula autumnalis. These larvae receive
different names depending on the geographical region where they are, such as red spider, summer mite
or harvest mites. The larvae have a distinctive orange color and feed on tissues of mammals and some
birds until completing their development. They adhere to the skin and introduce the cranial area or
stilostome in the dermis, to then secrete proteolytic enzyme substances that digest the tissue. The
infestation always occurs from the environment in shady areas such as forests, hedgerows and weedy
areas. Skin symptoms are often located in areas where larvae have easier access such as periocular,
interdigital, perioral, perianal and axillary region. The clinical pictures are usually pruritic, erythematous
and occasionally crusty.
Infectious diseases
A) Superficial pyoderma
Pyoderma is one of the most common causes of skin disease in dogs, but not in cats or horses. The
reasons for this increased canine predisposition are still under consideration (thinner stratum corneum,
absence of follicular plug at the entrance of canine hair follicle, higher skin pH, shortage of intercellular
lipids).
Etiopathogeny
Most cases of pyoderma are caused by Staphylococcus pseudointermedius, frequently isolated from the
nasal mucosa, perianal region and oropharynx of healthy dogs. Predisposing factors for the appearance
of surface pyoderma have been extensively studied and can be quickly summarized in the following
groups:
・ Animals with itching due to local trauma, rubbing or licking.
・ Use of long-term corticosteroid therapy in patients with chronic itching.
・ Inflammation, obstruction and / or follicular degeneration (e.g. Demodex)
・ Endocrine causes: Hypothyroidism, Cushing syndrome or diabetes.
Clinical signs
- Papular lesions, accompanied by erythema.
- Pustular lesions, which lead to the formation of epidermal collarettes.
- Scales and yellowish crusts.
- Multifocal alopecia in cases of folliculitis, in shorthaired breeds (moth-eaten appearance)
Typical cytological findings denote the presence of degenerated neutrophils by the action of bacterial
toxins, accompanied by phagocytized coccoid bacteria inside them.
Given the superficial nature of the disease and the emergence of the development of multiresistant
bacteria (MRSP) we face with increasing frequency, we should focus on the treatment of superficial
pyoderma using topical therapy, leaving systemic antibiotics for more stubborn or complicated cases.
B)
Malassezia Dermatitis
Dermatitis caused by Malassezia sp is a group of skin and ear conditions caused by saprophytic yeast,
which often cause intense pruritus.
Etiopathogeny
Malassezia pachydermatis is the most important commensal yeast in this disease, and it is considered as
a lipophilic, not lipid dependent, not forming mycelia and saprophytic yeast. It is usually found on the
canine skin inside the ear canal, mucocutaneous junctions and anal sacs.
Lesions in dogs can be localized or generalized. The most commonly affected regions are highly
moistened areas such as:
- Labial fold
- Ear canal
- Armpit and groin.
- Ventral neck region.
-
Perianal area.
Interdigital area.
Nail fold and nail shell.
In almost 70% of cases of cutaneous Malassezia there are concurrent diseases such as hypersensitivity,
seborrheic or endocrine conditions. And in up to 40% of cases, there is concurrent surface pyoderma due
to the symbiotic relationship of both infections.
In all cases, the itching of varying intensity is a constant symptom, and usually accompanied by a strong
rancid smell and erythematous areas with adherent yellowish scales in acute cases. In chronic or
recurrent cases, the skin thickens, appearing a very marked lichenification and hyperpigmentation.
The ideal sample collection technique is a dry surface scraping, application of acetate tape, sampling by
direct imprint with a slide, or by using a swab.
Yeasts are observed with the oil immersion objective (X1000) and are oval or rounded, with a
characteristic "peanut" aspect, often in groups frequently adhered to keratinocytes.
Allergic diseases
1) Atopic dermatitis
.
It is defined as an inflammatory pruritic and allergic disease, with a high genetic predisposition, and
commonly associated with the formation of IgE directed against environmental allergens.
The age of onset has been established between 6 months and 3 years, although it may vary depending
on the affected breed, and even geographic location or habitat of the patient.
Breeds that are predisposed are: Boxer, Shar Pei, French bulldog, West Highland White Terrier,
Dalmatian, English bulldog, Labrador Retriever, Golden Retriever and Yorkshire Terrier, among others.
Canine atopic dermatitis lesions are mainly located in:
- Ventral hairless or glabrous areas: Armpit and groin
- Peri-ocular region
- Chin
- Interdigital region.
- Pinna
- Elbow flexure
- Ventral neck region.
Currently, there is no reliable test to diagnose this disease. The diagnosis is based on clinical history,
clinical picture and ruling out other pruritic diseases.
Serologic or intradermal test should only be performed in order to identify specific allergens for the
initiation of a specific allergen immunotherapy, and never to confirm or exclude the diagnosis of atopic
dermatitis.
2) Food allergy
Definition
Food allergy has been broadly renamed as adverse food reaction (AFR), as some of these reactions do
not have true allergy nature and may be due to various kinds of phenomena such as enzymatic,
metabolic or idiosyncratic.
The age of onset is very variable in the case of the dog, one third of the reported cases are under 12
months of age, but has also been diagnosed in patients over 7 years with no clinical history of skin
disease. In cats, the average age of onset is 4 to 5 years, although again it is extremely variable.
There is no documented racial bias in the dog, although some authors suggest that the most susceptible
breeds to atopic dermatitis would also be at risk for AFR.
The lesion pattern is identical to that described for cases of atopic dermatitis. In some cases, less than
15%, concurrent gastrointestinal signs are also seen such as increased frequency of defecation, vomiting,
diarrhea or dyspepsia.
Currently, it is only possible to establish a diagnosis of FAR based on an elimination diet and rechallenge
with the offending food.
3) Flea bite allergic dermatitis (FAD)
Allergy to flea bites or FAD, is a hypersensitivity reaction, both immediate and delayed, to flea saliva,
which affects both the canine and feline species.
It is considered the leading cause of hypersensitivity in areas where the flea is endemic.
In the dog, the responsible protein of flea saliva in most FAD cases is Ctef1.
In the dog, the characteristic lesion distribution is a pruritic papular dermatitis affecting:
-
Lateral chest area
Flanks
Dorsal lumbar region
Tail
Perineal area
The visualization of the parasite or the droppings can help in the diagnosis, but often are difficult to
identify.
4) Allergic contact dermatitis
Allergic contact dermatitis is type IV hypersensitivity, characterized by a maculopapular reaction in areas
of low capillary density that causes severe itching.
The responsible element for contact dermatitis is a low molecular weight, liposoluble allergen.
In the dog, they have different origins such as plants, fabrics, household products and drugs.
Temporary removal of the suspected causative agent from the patient environment, at least for 14 days,
is used to confirm the diagnosis.
References.
- Favrot C, Steffan J, SeewaldWet al. A prospective study on the clinical features of chronic canine atopic
dermatitis and its diagnosis. Veterinary Dermatology 2010; 21: 23-30.
- Treatment of canine atopic dermatitis: 2015 updated guidelines from the International Committee on
Allergic Diseases of Animals (ICADA)Thierry Douglas J. DeBoer, Claude Favrot, Hilary A. Jackson,
Ralf S. Mueller, Tim Nuttall, Pascal Prélaud and for the International Committee on Allergic Diseases of
Animals 2015