Studies on human illness as a result of exposure to pathogens in a farming environment
Zoonotic Study 1: Budapest
Szita et al (1980) investigated animals as a source of Yersinia enterocolitica infection in humans. A total of 68 isolates from 3,115 animals belonged to four serogroups. A total of 556 animals in the Budapest Zoo were also examined. Yersinia enterolitica was found in fecal samples from one chimpanzee and one gibbon. Out of 877 persons in contact with animals, 4.56 percent had positive antigens for Yersinia enterocolitica serotypes compared to 0.33 percent in healthy controls. The study concluded that pigs should be regarded as a main source for human enteric yersinosis.
Zoonotic Study 2: United Kingdom
Trevena et al (1999) studied 63,000 stool samples collected and screened for verocytotoxin-producing E. coli (VTEC) O157:H7 over a three-year period (November, 1994 - October, 1997) by four participating microbiology laboratories in Cornwall and West Devon, United Kingdom. The investigation involved interviewing 69 confirmed cases (out of a total of 111 positive isolates) from among this sample population to assess the extent of any direct or indirect contact with farm animals.
The study indicated that farming families and workers, tourists, and casual farm visitors were observed to be associated with Zoonotic transmission of VTEC O157. It was also observed that the cattle were the primary animal reservoir for VTEC O157 in the study area. In addition, this research reported that the Health and Safety Executive ( HSE) had issued a revised guidance on farm visits to control the risk associated with VTEC O157 transmission.
Zoonotic Study 3: England
O'Brien et al (2001) discussed risk factors associated with the transmission of E. coli O157 as a result of exposure to the farming environment. This study was conducted between October, 1996 and December, 1997, in England. Data was obtained from 369 patients and 511 controls. A "Patient" was defined as a person with abdominal pain or diarrhea (3 or more loose stools in a 24 hour period) from whom Shiga Toxin-producing Escherichia coli O157 ( STEC O157) had been isolated by fecal culture from any of the 52 Public Health Laboratory Service (PHLS) laboratories in England.
This study concluded that sporadic STEC O157 infection in England was strongly associated with contact with the farming environment. The risk occurred in people not routinely exposed to the farming environment, i.e. people visiting open farms or who had recently started working on a farm. Direct Zoonotic and environmental transmission are important risk factors for outbreaks of STEC O157. The findings indicate that simple measures can be taken to prevent people from becoming infected, such as washing their hands after coming into contact with livestock or animal feces.
Zoonotic Study 4: United Kingdom
A letter to the editor of the journal “Emerging Infectious Diseases” discussed the relationships described in previous studies between enteric diseases and visits to petting zoos in England and Wales. Nearly 2 million people visit petting zoos and farms in the UK adding significantly to the rural economy. However, these farm visits can result in enteric disease.
Between 1992 and 2009, 55 outbreaks of infectious gastrointestinal diseases were associated with visits to petting farms in England and Wales. The most commonly acquired pathogens were Verocytotoxin-producing E. coli O157 (also known as Shiga-like toxin producing E. coli) and Cryptosporidium spp. These two pathogens were responsible for 97% of all outbreaks and 1,322 illnesses.
Cryptosporidium is a common zoonotic disease on farms, and is particularly present in preweaned lambs and calves. Contact with these animals, who are suffering diarrhea due to infection, carries a great risk of infection of humans. This explains part of the seasonal trend in Cryptosporidium incidence in the UK with an increase in spring as lambs and calves are born. However, while preweaned animals present a higher risk, a case-control study in England and Wales identified an association between infection with Cryptosporidium parvum and contact with any farm animal.
Another risk-factor associated with outbreaks of both pathogens was improper hand-washing facilities. The Cryptosporidium parasite survives alcohol-based hand sanitizers, making it important to provide soap and water at hand-washing stations on farms. This protective step is also key in preventing E. coli infections on the farm. The UK Health and Safety Executive provides standards for these facilities that petting farm operators are expected to meet.