Animals can develop skin problems just like humans. These problems usually cause itching, inflammation, alopecia, rash, and peeling [1].Dermatological diseases in dogs, cats, birds, and exotic species are the second reason for veterinary consultation, just behind preventive consultations. Among the most common symptoms in veterinary consultation, itching is the first reason, since most skin conditions produce an activation of the itching system [2]:

  • Fleas: Dogs are susceptible to fleas and can develop allergies that cause serious skin conditions.
  • Infections: Bacterial infections usually occur as a result of other conditions because when the animal scratches, it breaks the skin, allowing bacteria to infect the wound. Additionally, different types of mites can cause scabies, which is characterized by the production of skin lesions and hairless areas. Similarly, ringworm caused by a fungal infection also produces hairless, itchy patches.
  • Allergies: Dogs and cats can become allergic to the foods they eat. Food allergies usually cause itching in the nose, legs, ears, and around the anus. On the other hand, they can develop environmental allergies, which usually occur during hot seasons and typically have a genetic component, making some breeds more prone than others. Therefore, intense itching occurs in the nose, legs, ears, and ventral region.
  • Autoimmune diseases: These diseases occur when the immune system attacks the structure of the skin. Dermatitis is the most common autoimmune skin disease in pets. In this article, we will focus on atopic dermatitis in the most common pets: dogs and cats.

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Atopic dermatitis

Atopic dermatitis in pets, especially dogs and cats, is very similar to that in humans. In both cases, it causes itching, inflammation, and a decrease in the barrier function of the skin.

In a previous post we talked about the characteristics of atopic dermatitis in humans, however, today we want to focus on knowing how atopic dermatitis affects the most common pets. In dogs, the incidence of atopic dermatitis is between 5 and 10 times higher than in humans, 10 to 15%, and it is considered to have a multifactorial origin. While the incidence of feline atopic dermatitis is similar to that of dogs, with an average of 12.5% [3]. Among the causes that can trigger atopic dermatitis in dogs and cats, there are multiple factors:

Genetics

In the case of the dog, there is a genetic predisposition in which most of the genes involved are linked to the maintenance of the barrier function of the skin [4]. Likewise, it seems that certain dog breeds have a greater predisposition to developing atopic dermatitis. Thus, in German shepherds, different polymorphisms of chromosome 27 have been associated with a higher risk of suffering from this disease. More specifically, these polymorphisms affect both the plakophilin 2 gene, which encodes a structural protein of epithelial and immune cells, and its adjacent genes [5].

Other dog breeds with a greater predisposition to develop atopic dermatitis are Labrador, Golden Retriever, Boxer, Westhighland White Terrier, French Bulldog, Bull Terrier, American Cocker Spaniel, English Springer Spaniel, Poodle, Chinese Sharpei, Dachshund, Collie, Miniature Schnauzer, Lhasa Apso, Pug and Rhodesian Ridgeback. However, the predisposition of each race varies according to the geographical location [6].

Likewise, there seems to be a genetic component that predisposes certain breeds of cats to suffer from this disease. According to a study conducted on allergic cats, purebred cats had a much higher incidence of atopic skin than the rest of the cats studied [7], with Devon rex, Abyssinian and domestic shorthair cats being the most prone breeds [3].

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Barrier function

An important factor for the development of atopic dermatitis is the barrier function, a reduction in it results in a loss of transepidermal water and an increase in the entry of viruses, bacteria, and allergens into the epidermis. [8]. Filaggrin is one of the reduced structural proteins in the skin of people and animals with atopic dermatitis. However, in the case of the dog, the relationship between a decrease in this protein and atopic dermatitis does not seem entirely clear [9]. On the other hand, it is clear that the decrease in the barrier function in dogs depends on a modification of the ceramide composition of the epidermal lesions [10] and on the action of allergens altering the expression of corneodesmosomal proteins [11].

As in humans, the skin of dogs and cats with atopic dermatitis shows fungal dysbiosis measured by next-generation sequencing comparing skin samples from healthy and allergic animals [12].

Treatment

The choice of treatment by the veterinarian will depend on the severity of the lesions and the degree of itching that the animal presents. In addition, the owner’s ability to carry out the treatment must be taken into account and regularly reassessed [13].

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The most common treatments are like those used in humans. On the one hand, there are biological treatments, among which stands out the use of antibodies directed against the cytokines involved in atopic dermatitis, such as the interleukin IL-31. On the other hand, there are treatments to reduce inflammation and itching, such as immunosuppressants (glucocorticoids and cyclosporine) and Janus kinase enzyme inhibitors (oclacitinib) [14].

References
  1. Hill, P., Lo, A., Eden, C. A. N., Huntley, S., Morey, V., Ramsey, S., & Williams, V. (2006). Survey of the prevalence, diagnosis and treatment of dermatological conditions in small animals in general practice. Veterinary record, 158(16), 533-539.
  2. https://veterinariamrcan.com/blog/que-es-la-dermatologia-veterinaria/
  3. Ravens, P. A., Xu, B. J., & Vogelnest, L. J. (2014). Feline atopic dermatitis: a retrospective study of 45 cases (2001-2012). Veterinary dermatology, 25(2), 95–e28.
  4. Schamber, P., Schwab-Richards, R., Bauersachs, S., & Mueller, R. S. (2014). Gene expression in the skin of dogs sensitized to the house dust mite Dermatophagoides farinae. G3 (Bethesda, Md.), 4(10), 1787–1795.
  5. Tengvall, K., Kierczak, M., Bergvall, K., Olsson, M., Frankowiack, M., Farias, F. H., Pielberg, G., Carlborg, Ö., Leeb, T., Andersson, G., Hammarström, L., Hedhammar, Å., & Lindblad-Toh, K. (2013). Genome-wide analysis in German shepherd dogs reveals association of a locus on CFA 27 with atopic dermatitis. PLoS genetics, 9(5), e1003475.
  6. Jaeger, K., Linek, M., Power, H. T., Bettenay, S. V., Zabel, S., Rosychuk, R. A., & Mueller, R. S. (2010). Breed and site predispositions of dogs with atopic dermatitis: a comparison of five locations in three continents. Veterinary dermatology, 21(1), 118–122.
  7. Hobi, S., Linek, M., Marignac, G., Olivry, T., Beco, L., Nett, C., Fontaine, J., Roosje, P., Bergvall, K., Belova, S., Koebrich, S., Pin, D., Kovalik, M., Meury, S., Wilhelm, S., & Favrot, C. (2011). Clinical characteristics and causes of pruritus in cats: a multicentre study on feline hypersensitivity-associated dermatoses. Veterinary dermatology, 22(5), 406–413.
  8. Mineshige, T., Kamiie, J., Sugahara, G., & Shirota, K. (2018). A study on periostin involvement in the pathophysiology of canine atopic skin. The Journal of veterinary medical science, 80(1), 103–111.
  9. Marsella, R., Papastavros, V., Ahrens, K., & Santoro, D. (2016). Decreased expression of caspase-14 in an experimental model of canine atopic dermatitis. Veterinary journal (London, England: 1997), 209, 201–203.
  10. Reiter, L. V., Torres, S. M., & Wertz, P. W. (2009). Characterization and quantification of ceramides in the nonlesional skin of canine patients with atopic dermatitis compared with controls. Veterinary dermatology, 20(4), 260–266.
  11. Olivry, T., & Dunston, S. M. (2015). Expression patterns of superficial epidermal adhesion molecules in an experimental dog model of acute atopic dermatitis skin lesions. Veterinary dermatology, 26(1), 53–18.
  12. Meason-Smith, C., Diesel, A., Patterson, A. P., Older, C. E., Johnson, T. J., Mansell, J. M., Suchodolski, J. S., & Rodrigues Hoffmann, A. (2017). Characterization of the cutaneous mycobiota in healthy and allergic cats using next generation sequencing. Veterinary dermatology, 28(1), 71–e17.
  13. Saridomichelakis, M. N., & Olivry, T. (2016). An update on the treatment of canine atopic dermatitis. Veterinary journal (London, England : 1997), 207, 29–37.
  14. Gedon, N.K.Y., Mueller, R.S. Atopic dermatitis in cats and dogs: a difficult disease for animals and owners. Clin Transl Allergy 8, 41 (2018).

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