A review of canine‐related zoonotic dermatologic diseases

This is the authors' abstract. We don't add key points for this paper.

Zoonotic diseases, or zoonoses, are infections that can be transmitted between animals and humans. According to the World Health Organization, there are over 200 known types of zoonoses, which various pathogens, including bacteria, viruses, parasites, and fungi can cause. The global incidence of zoonotic diseases is increasing because of several factors, including the destruction of natural habitats through urbanization, intensive farming, livestock production, worldwide travel and trade, and the impacts of climate change.1 Although most zoonoses are associated with direct or environmental exposure to livestock, rodents, or wild animals, the review article in this issue of the Journal by Klein et al. serves as an important reminder that common household pets, such as dogs, can also be significant sources of various zoonotic diseases.2 Perhaps the most common canine infections and potential zoonoses most dog owners are familiar with are rabies and intestinal parasitic infections. Dogs are vaccinated against rabies, and most veterinary practices offer regular anthelmintic treatments.3 However, numerous lesser-known infections can spread to humans and cause an eruption, systemic symptoms, or sometimes even life-threatening syndromes. Klein et al. provide a comprehensive summary of these diseases, highlighting several important clinical pearls. For instance, Rocky Mountain spotted fever (RMSF), a potentially deadly bacterial infection caused by the pleomorphic gram-negative bacteria Rickettsia rickettsii, most often presents with a palmoplantar exanthem along with fever, severe headache, and other symptoms. “Spotless” or “almost spotless” disease versions with no or only minimally visible rash have been reported. Klein et al. point out that RMSF is more likely to present in this atypical fashion in skin of color (SOC) patients. Therefore, a high index of suspicion is required to make the correct and potentially lifesaving diagnosis in this cohort of patients. Similarly, Lyme disease is rarely diagnosed early in the SOC patient population. The classic targetoid lesions of erythema chronicum migrans are either absent or are missed upon examination. Therefore, these patients are more likely to present later with disseminated disease, often with neurologic symptoms.2 Another interesting pearl discussed in this review adds to the differential diagnosis of pruritic exanthems. When diagnosing scabies, a detailed exposure history is critical. Patients living in nursing homes, homeless shelters, or the incarcerated are more likely to harbor scabies mites, also known as Sarcoptes scabiei (S. scabiei) var. hominis.4 Interestingly, dogs can carry scabies mites as well, albeit a different variety, called S. scabiei var. canis. Canine scabies are highly contagious and can cause an intensely pruritic rash in humans. The hands, arms, axillae, and abdomen are most affected, while the typical scabies predilection sites, such as the interdigital web spaces or the genitalia, are often spared.2 Finally, it is worth highlighting that dog owners are not always the primary victims of zoonoses. Microsporum canis is a well-known and common cause of dermatophyte infections in humans. Malassezia pachydermatitis, on the other hand (part of the normal skin flora in dogs), is unlikely to cause an infection in immunocompetent patients. However, it can colonize the skin of healthy individuals, and this yeast can be transmitted to neonates and immunocompromised patients. Reports of severe M. pachydermatitis infections in intensive care units have been well-documented and were traced back to asymptomatic healthcare workers who owned dogs and were caring for patients with a weakened immune system.5 There are numerous zoonoses that dogs can transmit. Children under the age of five, the elderly, pregnant women, and immunocompromised patients are at considerably higher risk of contracting these diseases.2 Prevention and early diagnosis are key to preventing potentially severe sequelae of many of these etiologies. Diagnosing the disease early in pets, proper hand hygiene, and avoiding direct contact with the urine and feces of the animals are key preventative measures. Early diagnosis, however, is only possible if the physician is aware of these often rare but increasingly more prevalent and frequently missed diagnoses.