Summary of Literature on Fair & Petting Zoo-Related Outbreaks

Kudva et al (1996) discussed the natural prevalence of Escherichia coli O157:H7 in sheep. The results of this study concluded that Escherichia coli O157:H7 is observed to be naturally occurring in sheep. Thus, sheep can be considered as a host for human pathogens. This research also added that lamb meat does not necessarily have to be cross-contaminated with Escherichia coli O157:H7, but it could be contaminated by its pre-harvest source.

Kudva et al (1997) studied the enterohemorrhagic Escherichia coli (EHEC) and some Shiga toxin-producing E. coli (STEC) which is associated with human and animal diseases. The important finding from this study was that sheep shed non-E. coli O157:H7 STEC serotypes which are often observed in human infections. This report showed that sheep under the case control study shed a variety of STEC strains including Escherichia coli O157:H7 that can act as potential pathogens for humans.

A MMWR Weekly report (July, 1998) provided a compendium of measures to control Chlamydia psittaci infection among humans and pet birds. Psittacosis - also known as parrot disease, parrot fever, and ornithosis – can cause severe pneumonia and other serious health problems among humans. Approximately 800 cases of psittacosis (infection with Chlamydia psittaci) were reported to the CDC over the period of 1987 to 1996. Most of these cases resulted from exposure to pet birds such as parrots, macaws, cockatiels, and parakeets. The nature of the transmission was primarily aerosolization of respiratory secretions or dried feces of infected birds, though bird bites, mouth-to-beak contact and handling of plumage were also contributing factors.

The CDC issued a press release in August of 1999 (CDC Media Relations, 1999) regarding a bear who had placed zoo visitors at risk for rabies. The bear died of rabies, and it was estimated that up to 400 people who had had contact with the bear in the prior month were at risk. To be exposed, the people must have had contact with the bear’s saliva. The exposure risk was also addressed in a MMWR Weekly (September, 1999).

A MMWR Weekly report (November, 1999) summarized reports received by CDC from approximately 16 state health departments over the period of 1996-1998 regarding Salmonella infections in persons who had direct or indirect contact with reptiles. Most of the transmissions were from human-pet contact (e.g. pet turtles, lizards and snakes). The risks of transmission of Salmonella spp. can be reduced through education, hand washing, and by preventing contact with populations at greater risk such as infants and immunocompromised persons.

Nowotny and Deutz (2000) submitted a letter to the journal Emerging Infectious Diseases in which they discussed the role of physicians and veterinarians in preventing Zoonotic diseases in immunocompromised persons. They discussed serological findings that demonstrated that veterinarians have been exposed to a much greater range of Zoonotic diseases as a result of profession-specific risk factors. Knowledge of this exposure allows them to take adequate measures to prevent infections, and makes them qualified to advise pet owners and persons of other professions who are at high risk.

Hatchette et al (2001) studied illnesses of goat workers while performing goat abortions in rural Newfoundland, Canada, in the spring of 1999. An epidemiologic investigation and serologic survey were conducted to determine the number of infections, nature of illness, and risk factors for infection. Thirty-seven percent of the outbreak cohort had antibody titers to Q fever. Risk factors examined included contact with goat placenta, smoking tobacco, and eating goat cheese. Overall, 56% of the goats were seropositive for antibodies to C. burnetti.

Oh et al (2002) discussed Mycobacterium tuberculosis infection diagnosed in various animals in the Los Angeles Zoo. Six cases of M. tuberculosis were identified in Los Angeles Zoo between the periods of 1997 to 2000. The infected animals included two Asian elephants, three Rocky Mountain goats, and one black rhinoceros. The investigation did not find any active tuberculosis cases in humans, though a tuberculin skin test conversion was observed to be associated with training elephants and attending an elephant necropsy. The report recommended that strict infection control measures should be followed during animal medical procedures to minimize the risk of transmission from animals to humans.

Valcour et al (2002) published a paper examining associations between indicators of cattle density in farming areas and the incidence of Shiga toxin-producing E. coli infection. Several indicators of cattle density were used. A positive relationship was found. Possible causal relationships included consumption of unpasteurized milk, drinking water from shallow wells, direct contact with cattle, and application of manure to land.

Ogden et al (2002) discussed the survival of Escherichia coli O157:H7 in pastures. The objective of this research was to monitor the decay of Escherichia coli O157:H7 in loamy sand on a scout campsite. The environmental investigation studied soil and sheep feces samples, and concluded that the organisms were viable for 15 weeks, indicating the potential threat to human health when shedding of the microbes from various farm animals contaminates the environment.

Hussein et al (2003) studied the Vero toxin producing Escherichia coli in sheep grazing. This research was focused on identifying the Vero toxin producing Escherichia coli (VTEC) prevalence in two groups of ewes (n=20) grazing in Nevada from the summer of 1999 to the summer of 2000. A random sample (n=504) of isolates were screened for the presence and expression of the toxic genes (VT1 and VT2). Forty-one VTEC isolates were identified, of which 16 were having only VT1 gene and 25 having both VT1 and VT2 genes. The authors reported that though sheep products have not been linked with human illnesses so far, their role as a food safety factor should not be ignored. They further concluded that as the two VTEC serotypes responsible for human infection were being shed by the sheep under this case control study, it would be beneficial to identify VTEC –positive sheep before slaughter.

Blanco et al (2003) discussed the prevalence of Escherichia coli in Spain. There have been 7 outbreaks identified to be caused by E. coli, of which six were caused by Escherichia coli O157:H7 and one outbreak was caused by Escherichia coli O111:H (-). The study suggested that numerous bovine and ovine VTEC serotypes were detected in Spain associated with serious illnesses caused in humans. The researchers added that this confirms that ruminants are important reservoirs for pathogenic VTEC.

Erdozain et al (2012) observed visitors to petting zoos, noting frequently observed risky behaviors, including touching hands to face within animal-contact areas; animals licking visitors' hands; and visitors drinking within animal-contact areas. The authors observed that 37% of visitors attempted some type of hand hygiene, and were more likely to do so when a staff member was present within or at the exit to the animal-contact area. Visitors at zoos with a fence allowing only partial contact to animals were 2.3 times more likely to wash their hands than visitors allowed to enter the animal area for contact. The authors noted that inconsistencies in tool availability, supervision of animal contact, and risk communication were inconsistent or poor at the petting zoos visited.