Plague

During a 1974 outbreak of plague in New Mexico, USA, 7 cases of bubonic plague were investigated. One patient noticed flea bites the morning after he allowed his flea-infested cat to share his bed (4). Similarly, in a series of 23 cases of plague related to cat exposure, a 9-year-old boy from Arizona had handled and slept with a sick cat (5). Another case, which occurred in 1983 in New Mexico, was likely acquired after indoor/outdoor cats slept with the patient (6). More recently, a 2008 matched case–control study (7) surveyed 9 plague survivors, 12 household members of these survivors, and 30 age- and neighborhood-matched controls about household and individual exposures. Four (44%) survivors and 3 (10%) controls (matched odds ratio 5.7, 95% confidence interval [CI] 1.0–31.6) reported sleeping in the same bed with a pet dog, which remained significantly associated with infection in a multivariate logistic regression model (p = 0.046). Such behavior is of concern because dogs may facilitate transfer of infected fleas into the home and, unlike cats, rarely show clinical signs of infection that could serve as a warning.

Chagas Disease

A study in northwest Argentina showed that dogs and cats infected with the Chagas disease agent, Trypanosoma cruzi, increased risk for domestic transmission of T. cruzi to the Chagas disease vector, Triatoma infestans bugs (8). Infection rates were significantly higher when infected dogs shared sleeping areas with humans than when they did not (relative risk 1.79; 95% CI 1.1–2.91).

Cat-Scratch Disease

Cat-scratch disease is mainly transmitted to humans when they are scratched by a cat that harbors Bartonella henselae–infected fleas and flea feces (9). However, a few documented cases have been associated with sleeping or being licked by a household pet. For example, a systemic case of cat-scratch disease with hepatic, splenic, and renal involvement caused by B. henselae was diagnosed by immunofluorescence assay, PCR, computed tomography, and histologic examination. The patient was a 9-year-old aboriginal girl from Taiwan, who had been sleeping with a cat at night (10). In addition, B. hensalae infection was suspected and confirmed by serologic testing of a 50-year-old man from Japan, who had left cervical lymphadenopathy and owned a dog that often licked his face (11). In a study of risk factors associated with cat-scratch disease in Connecticut, USA, case-patients were more likely than matched controls to have been scratched or bitten by a kitten, licked on the face by a kitten, slept with a kitten, or combed a kitten (12).

Pasteurella spp. and Capnocytophaga canimorsus Infections

Several reports describe human infections by Pasteurella spp. that were acquired after close contact with pets, including sharing a bed, being licked by, or kissing the pets. In 1985, a case of meningitis caused by P. multocida in a 60-year-old housewife living in the United Kingdom was reported (13). She admitted to regularly kissing the family dog. P. multocida isolates from buccal and nasal swabs of the dog were identical to isolates from the woman. Two cases of meningitis in newborn children (<1 month of age) have been reported; 1 was associated with a pet cat stealing a baby’s pacifier and using it as a toy, and the other was associated with a pet dog that often licked the baby’s face (14). Of 38 reported cases of P. multocida meningitis in infants, 27 (87%) of 31 infants that had been exposed to animals had been exposed directly or indirectly to the animals’ oropharyngeal secretions through licking or sniffing (14). A case of P. multocida infection of a hip replacement site occurred in a 69-year-old man (15). This man indicated that the dog had shared his bed before and after his operations, sleeping under the covers on the side of the affected leg, as it had done every night for the past 10 years (15).

Being licked by pets is a common source of human infection with P. multocida (16–19), but in a case described by Wade et al. (16), transmission to an infant occurred from another person. After the 2 family dogs had licked the hands of the infant’s 2-year-old brother, the older boy allowed the infant to suck on his little finger. Heym et al. (18) describe a case in France in which a total knee arthroplasty site became infected with P. multocida after the patient’s dog licked a small wound on the third toe of the leg that had been operated on. In another case, P. multocida was cultured from a wound abscess that developed in a 48-year-old obese woman 6 weeks after hysterectomy and panniculectomy for endometrial cancer (20); her cat had licked the wound. In France, meningitis caused by P. multocida developed in a 67-year-old patient with chronic, purulent otorrhea of the right ear. His dog frequently licked the patient’s right ear (21), and cultures from the dog's saliva also grew P. multocida. The isolates had identical biochemical patterns, and pulsed-field gel electrophoresis (PFGE) confirmed genotypic similarities. After digestion of genomic DNA with the infrequently cleaving restriction endonuclease SmaI, banding-pattern analysis showed clonal similarity between the isolates from the patient and the dog. In Japan, paranasal sinusitis caused by P. multocida was diagnosed for a 39-year-old woman with rhinorrhea and headache (22). The patient’s cat awakened her every morning by licking her. P. multocida isolates from the woman’s nasal discharge and the cat’s saliva were similar with respect to biochemical properties, serotype, and drug susceptibility.

Kissing pets can also transmit zoonoses. A study in Japan of 24 pet owners (11 cats and 3 dogs) found no Pasteurella spp. in the oral cavity of the 19 owners who had not kissed their cat, but isolated P. stomatis from the oral cavity of 1 of 2 owners who had kissed their cat and in 2 of 3 dog owners who had kissed their dog (23). Also in Japan, meningitis caused by P. multocida developed in a 44-year-old woman who admitted that she was regularly kissing the dog’s face and feeding it by transferring food mouth to mouth (24). As suggested by Kawashima et al. (24), “recent increase in pet ownership is likely to increase human exposure to P. multocida.” These authors identified at least 2 other cases of P. multocida meningitis between 2000 and 2010; these cases developed after the patients kissed a pet dog and a pet rabbit.

Capnocytophaga canimorsus infections in humans have been associated with being licked by or sleeping with a dog or cat. In Finland from 1988 through 1994, several cases of C. canimorsus septicemia were identified; 2 cases were associated with sleeping with and/or being licked by a pet (25). For an 81-year-old woman with cellulitis of the right leg and an ulcer between the fourth and fifth toe, C. canimorsus was isolated from a blood culture. This patient indicated that she slept with her cat in her bed and that the cat licked her feet and toes. A 60-year-old patient with chronic eczema died of septic shock and renal failure and disseminated intravascular coagulation caused by C. canimorsus (25). The ulcerous chronic eczema of his legs was the most probable port of entry for the organism because his dog used to lick his legs. In Kansas, USA, a splenectomized 44-year-old man died after infection with C. canimorsus (26). The man had lived in a trailer and collected scrap metal to sell; he had several cuts and scratches on his forearms and hands. His recently acquired German shepherd puppy reportedly licked the open abrasions on the man’s hands, but no bite was reported. In Australia, septicemia and multiorgan failure developed in a 48-year-old woman after her fox terrier puppy licked a minor burn wound on the top of her left foot (27).

Staphylococcus intermedius Infections

Staphylococcus intermedius is a common commensal bacterium in dogs and cats and has rarely been identified as causing human infection (28). However, in Japan, S. intermedius developed in the mastoid cavity of a 51-year-old woman after mastoidectomy for chronic otitis media with cholesteatoma (28). Her dog had licked her ears, and bacterial strains from the dog’s saliva and the patient’s otorrhea were confirmed by PFGE to be identical. Similarly, a 28-year-old woman with a history of endoscopic pituitary adenoma resection reported 3 weeks of foul-smelling nasal discharge (29). Nasal endoscopy indentified a purulent sinus infection caused by methicillin-resistant S. intermedius. Cultures from the patient's pet bulldog also grew S. intermedius strains that were confirmed by PFGE to be identical to those of the patient. The patient reported having had close physical contact with her dog, including frequent licking of her face, and that the dog had recent bouts of pyoderma requiring treatment with antimicrobial drugs.

Methicillin-Resistant Stapylococcus aureus Infections

A 48-year-old man with diabetes and his wife had recurrent methicillin-resistant Staphylococcus aureus (MRSA) infections (30). Culture of nares samples from the family dog grew mupirocin-resistant MRSA that had a PFGE chromosomal pattern identical to the MRSA isolated from the patient's nares and his wife's wound. The couple reported that the dog routinely slept in their bed and frequently licked their faces. Further recurrence of MRSA infection and nasal colonization in the couple was prevented only after successful eradication of MRSA from the dog's nares.

Rabies

In many developing countries, being licked by dogs that are rabid or suspected to be rabid is considered to pose a major risk. A survey of rabies exposure among 296 Norwegian missionaries and foreign aid workers traveling abroad showed that of 48 persons for whom postexposure vaccination was recommended, two thirds had only cared for or been licked by the suspected rabid animal (31). Rabies remains a problem in Southeast Asia, where many backpackers visit each year. In the early 1990s, foreign travelers (74% of whom were European), who had been in Thailand for an average of 17 days, were surveyed about potential rabies exposure during their visits. Among 1,882 travelers, 1.3% had been bitten and 8.9% had been licked by dogs (32). During May–June 2008, another survey of 870 foreign backpackers (median age 25.5 years) in Bangkok, Thailand, found that 3.56% had been licked by a dog (33).

Parasitic Infections

In the United States, the most common parasitic zoonoses associated with dogs are caused by hookworms (Ancylostoma spp.) and roundworms (Toxocara canis) (2). In the Netherlands, prevalent parasitic zoonoses are caused by Toxocara spp., Giardia spp., Cryptosporidium spp., and Toxoplasma spp (1). Among the ways that toxocariasis can be transmitted to humans, contact with embryonated eggs on a dog's hair coat was recently proposed (34). Similarly, a recent study in the Netherlands identified Toxocara spp. eggs on the fur of 18 dogs (12.2%) and 2 cats (3.4%) and in the feces of 4 dogs and 1 cat (1). That same study found Giardia spp. in the feces of 14 dogs and 3 cats and Cryptosporidium spp. in feces of 8 dogs and 1 cat (1). A case of Cheyletiella blakei infection was reported in a 76-year-old woman with pruritic eruption of vesicles and bullous lesions on her trunk and arms (35). Cheyletiella spp. dermatitis was suspected because of the appearance and distribution of the elementary lesions and because before the eruption, the patient had acquired a cat that sometimes slept in her bed. The diagnosis was confirmed by a veterinary examination and isolation of C. blakei from the cat's skin. The patient’s condition resolved after the cat was treated with ivermectin, the household was disinfected with permethrin, and the patient was treated with benzyl benzoate.