Agriculture Reference
In-Depth Information
as fertilizers. The latter practice is increasingly controversial in the developed world
since research has shown that viral and bacterial pathogens are capable of extended
survival or persistence in agricultural soils (Bagdasaryan 1964; Natvig and others
2002; Islam and others 2004, 2005; Nicholson and others 2005). Research on the
behavior of pathogens under fi eld conditions has focused on vegetable production
systems, and comparatively less is known about their persistence or the risk of transfer
in fruit production systems. In spite of defi ciencies in data for specifi c crops there is
a clear trend toward reducing or eliminating the use of untreated animal wastes as soil
amendments or fertilizers for all horticultural crops destined for the fresh or fresh- cut
market, including fruit. Industry-based associations or regulatory bodies in many
jurisdictions now either encourage or enforce treatment of animal wastes by physical
(heat, irradiation) or biological (composting) means before fi eld application to reduce
or eliminate the associated risk.
Direct crop contamination with animal feces is more diffi cult to manage. Although
livestock access to production sites can be restricted—by fencing, for example—
some species of wildlife are diffi cult or impossible to deter. Bird control is an
ongoing, signifi cant source of economic losses in fruit or berry production despite the
deployment of a variety of passive or lethal measures. The feces of many avian
species have been shown to contain pathogens such as
Salmonella
or
E. coli
O157:H7
(Wallace and others 1997). None of the fruit-associated outbreaks reported to date
have been conclusively linked to contamination by wildlife feces. However, there is
convincing evidence that apples used in the manufacture of unpasteurized apple juice
responsible for some outbreaks caused by
E. coli
O157:H7 may have been contami-
nated by contact with the feces of infected deer (Riordan and others 2001; Garcia and
others 2006 ).
Invertebrates have been shown to acquire human pathogens through contact with
animal waste or environments polluted by animal feces. Insects can carry and excrete
human pathogens (Xu and others 2003; Alam and Zurek 2004) and insect-mediated
transfer to fruit has been demonstrated experimentally. For example, Janisiewicz and
others (1999) showed that infected fruit fl ies can transfer
E. coli
O157:H7 to exposed
apple tissues. Nematodes (Gibbs and others 2005) and slugs (Sproston and others
2006) have also been shown to excrete human pathogens and may serve as reservoirs
in soil or the production environment. However, the role of invertebrates as vectors
for the transmission of human pathogens in commercial production systems and the
inherent risk are presently unknown due to a dearth of fi eld data.
Contamination through Irrigation Water
Water is a well-recognized vector in disease transmission. Enteric viral, bacterial, or
single-celled pathogens in animal waste can be carried in large numbers over great
distances through natural or man-made waterways. The strong association between
irrigation water quality and produce safety is supported by epidemiological data from
several incidents involving vegetables wherein the implicated etiological agents were
recovered from infected individuals and irrigation water (Takkinen and others 2005).
There are no similar reports for fruit-associated outbreaks, although fi eld or experi-
mental evidence points to the potential role of irrigation water as a vector for con-
tamination (Espinoza-Medina and others 2006). For example, Materon and others
