Many diseases and infections are contagious to humans. They are called zoonoses. Among these here are listed the skin zoonoses that should be identified as soon as possible to reduce the risk to human health. The experience of the mode of transmission (direct or indirect contact via the environment or via a carrier), the risk assessment for human health, the hygienic and therapeutic management of these cases is indispensable for the veterinarian who always keeps in mind that the most susceptible to catch a zoonosis are children under 10 years.
The fleas :
Infestations due to fleas are extremely common. The flea species representing 95% of the population is: Ctenocephalides felis felis (The flea in the cat).
In humans, a flea bite provokes nodules (small pustules) characterised by a small dot in the centre, often 2 to 3 bites in a row. As fleas cannot jump further than 70 cm, the injuries are mainly on the legs. However, the presence of the dog on its owner's bed may alter the classic clinical injury localisation.
This dermatosis caused by a mite of the Cheyletides family is often underestimated. These parasites live on the skin surface and feed on broken skin. The environment is an important source of infestation, as these parasites can live for a month without the guest.
Human infection is common (20 to 80% of people in contact) especially if contacts with the infested animal are close. The lesions are located in the physical areas that come into contact with the infested animal. The dermatitis is characterised by intense itching and itchy nodules that are solitary or in groups of 3. These lesions quickly become vesicular, pustular, scabby and often develop a central necrosis-like zone.
Sarcoptes mange :
Sarcoptes mange is a contagious parasitic dermatosis, originating from mite presence of the family Sarcoptides: Sarcoptes scabiei var canis, which live in the cornea of the dog and dig galleries.
The risk of infection to humans is in +/- 25 à 30 % cases of the dog's skin (close and repeated contact; the scabies mite has the ability to penetrate light clothing). The scabies mites of dogs do not reproduce in the skin of humans, they can only survive on the skin surface for a few weeks without ever digging galleries. In humans, the lesions are mainly located in the contact areas: upper arms, hands, legs, areas with thin skin (abdominal girdle, chest...). The skin lesions are characterised by nodules and small itchy crusts. The scabby grooves, described during human infestation by S scabiei var hominis, are not observed during human infestation by canine Sarcoptes mange. The cycle does not usually establish in humans and the lesions therefore disappear spontaneously in a few days after the dog has healed or contact with that animal has ceased.
The dermatophytes (the ringworm)
The dermatophytes are contagious and superficial infections caused by keratinophilic and keratinolytic fungi called dermatophytes and belong to the species Microsporum, Trychophyton and Epidermophyton. They represent the main cause of skin diseases in cats, but also in dogs, rodents, lagomorphs, horses, retired animals ... The dermatophytes are, in connection with their main ecological niches, classified into geophilic species (colonise the soil), zoophilic and anthropophilic, which are obligatory parasites adapted to their main reservoir, animal or human.
Microsporum canis is mostly isolated in domestic animals. These fungal diseases are of great concern because they are potential zoonoses and represent a real therapeutic challenge when a feline community is infested.
The dermatophytes are extremely contagious to humans. They induce infections localised on certain parts of the body called : tinea capitis, tinea favosa, tinea barbae, tinea corporis (tinea circinata), tinea cruris, tinea pedis, ninea manus...
Sporotrichosis is a systemic or subcutaneous fungal disease that originates from the soil. It is mostly found in tropical countries. It originates from Sporothrix schenckii, a dimorphic fungus. This fungal disease benefits from a wound to infect an individual.
Sporotrichosis is very contagious to humans. Humans become infected through direct contact with tissue or discharge from infected animals. The most common clinical form is skin or subcutaneous, but systemic forms with lung infections, arthritis or meningitis have also been described. In subcutaneous sporotrichosis, 2 main forms have been described: infectious lymphangitis and " fixed " infection. In the lymphangitis form, a skin nodule emerges and forms a small ulcer, the lymphatic vessel becomes inflamed and swollen, and many nodules emerge along the lymphatic pathway. In the "fixed" form (15% of cases), the infection remains local and emerges through a granuloma that becomes an ulcer.
Pox virose :
Pox virose is a viral dermatosis found in the cat and less commonly in the dog. It is caused by a virus of the Orthopox type. It mainly attacks hunting cats living in a rural area. Infection usually occurs through bites from small wild rodents (field mouse, vole...) or, more rarely, via cattle. Human infection induced by an infected cat is rare and is mainly observed in immunodepressed individuals. Humans present with painful nodules, vesicles, pustules with erythema (redness) and annular oedema. They develop into crust formation and ulcers. Lymphadenopathy (enlargement of lymph nodes) and fever are often observed. Interpersonal transmission of the infection to the virus Cowpox has not been described to date.