Agriculture Reference
In-Depth Information
Human Pathogens Associated with Animal Wastes
Epidemiological investigations of produce contamination on farms have frequently
looked into animal feces as potential sources and have focused on the use of raw
manure or compost as fertilizer; adjacent land use with livestock or poultry operations;
and presence of wild animals such as deer, other mammals, and birds (Beuchat 2006;
CalFERT 2007). In addition, irrigation water and foliar application of compost tea are
important sources for produce contamination in the fi eld. Therefore, fully understand-
ing the prevalence, survival, and transmission of human pathogens in animal feces is
essential for developing intervention strategies for controlling produce contamination
on farms.
Animal Wastes
According to the 2002 census of agriculture, the livestock and poultry industries
produced ca. $106 billion worth of products sold in the U.S., which included over 74
million cattle and calves, ca. 185 million hogs and pigs, and ca. 8.5 billion broilers
and other meat-type chickens (USDA 2002). With such a large number of livestock
and poultry raised in this country, these animals also generate substantial volumes of
manure commonly called wastes. An estimated 1.36 billion tons of manure are pro-
duced annually in the United States, of which approximately 90% is generated by
cattle, 5% by poultry, and the rest by swine (US SAC 1998). Wastes generated from
animal-based agricultural enterprises come from cattle feedlots, dairy farms, poultry,
swine, pastures, and meat and poultry processing plants.
Human Pathogens in Animal Wastes
Manure is the mixture of animal excreta such as feces and urine, bedding materials,
and other secretions from the animal (Himathongkham and others 1999). Many species
of microorganisms are present in animals and their feces, including
Aeromonas
hydrophila, Arobacter butzleria, Bacillus anthracis, Brucella abortus, Campylobacter
jejuni, Chlamydia psittaci, Clostridium perfringens, Clostridium botulinium, Coxiella
burneti, E. coli, Erysipelothrix rhusiopathiae, Francisella tularensis, Leptospira
spp.,
L. monocytogenes, Mycobacterium tuberculosis, Mycobacterium paratuberculosis,
Salmonella
spp., and
Yersinia
spp. (Sobsey and others 2001).
Animal manure frequently contains enteric microorganisms that are human patho-
gens (Zhao and others 1995; Pell 1997; Kudva and others 1998). Among those 11
agents associated with produce-borne outbreaks, as identifi ed by the National Advisory
Committee on Microbiological Criteria for Foods (NACMCF 1999),
E. coli
O157:H7,
Salmonella
spp., and
L. monocytogenes
are responsible for the majority of outbreaks.
E. coli
O157:H7 are carried by ruminants, especially cattle, and are shed in their feces
(Meng and others 2001).
Salmonella
spp. inhabits the intestinal tracts of a variety of
animals with poultry and eggs remaining as a predominant reservoir (Wray and Davies
2003 ).
L. monocytogenes
is widely distributed in the environment and is associated
with animal feces, decaying vegetation, soil, silage, water, and fresh vegetables
(Swaminathan 2001 ).
Fecal excretion of pathogens by animals can be affected by various factors, includ-
ing species of animals, age, health status, diets, seasonal effect, and farm practices
