Means of Transmission

Workers in production agriculture may come in contact with animals and animal products in the course of their job tasks. Table 27.1 lists the circumstances of contact where disease can be transmitted from animals to humans.

Table 27.1. Means of transmission from animals to humans. Animal bites Animal secretions Saliva Semen

Vaginal secretions Skin contact Veterinary care

Procedures such as castration, dehorning Pushing, pulling animals Feeding the young Carcass handling Slaughter Necroscopy Eggs Milk

Handling freshly cooked or uncooked meat or poultry products Eating or drinking uncooked or unpasteurized products before or during processing Manure Urine Feces Veterinary treatment

Source: Data from Jemmi et al. (1), Spencer et al. (3), Dutkiewicz (4), Guan and Holley (5), and Weber and Rutala (6).

A key problem is the lack of foot protection so that the unprotected feet of workers come in contact with feces of the animals. The fecal-hand route of transmission is also critical. Perhaps the most insidious and difficult to control is the consumption of raw poultry and meat products by workers in farms and processing plants. Many people in agriculture are living on subsistence or below-subsistence wages and consume products off the processing lines. Many of these products are not fully processed and may contact pathogens that have not been killed through cooking or irradiation (see Chapter 2) (Table 27.1) (3,4).

The improper handling of manure is a major source of disease, including the use of manure on food crops, the discharge of manure into community water sources, and the spread of manure onto areas where children play. In Canada, an outbreak of Escherichia coli O157:H7 was traced to organic growers who contaminated their produce with cow manure containing E. coli. Also in Canada, an outbreak of Citrobacter freundii infections was associated with parsley originating from an organic garden in which pig manure was used. Other documented infections of humans from manure-contaminated foods includes Listeria monocytogenes in cabbage contaminated by sheep waste, Cryptosporidium spread by municipal water contaminated by cattle, Salmonella hartford in food prepared by contaminated water from a shallow well polluted with poultry manure, and Pleisomonas shigelloides infection associated with well-water contaminated by poultry manure (5).

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