At the end of the twentieth century, less than 5% of the workforce in industrialized nations is employed in agriculture, while nearly 50% of the worldwide workforce is engaged in agriculture (Sullivan et al. 1992). The work varies from highly mechanized to the manually arduous. Some agribusiness has been historically international, such as plantation farming and the growing of export crops. Today, agribusiness is international and is organized around commodities such as sugar, wheat and beef. Agriculture covers many settings: family farms, including subsistence agriculture; large corporate farms and plantations; urban farms, including specialty enterprises and subsistence agriculture; and migrant and seasonal work. Crops vary from widely used staples, such as wheat and rice, to specialty crops such as coffee, fruits and seaweed. Moreover, the young and the old engage in agricultural work to a greater extent than any other industry. This article addresses health problems and disease patterns among agricultural workers except for livestock rearing, which is covered in another chapter.

Overview

The image of agricultural work is that of a healthy pursuit, far from congested and polluted cities, that provides an opportunity for plenty of fresh air and exercise. In some ways, this is true. US farmers, for example, have a lower mortality rate for ischemic heart disease and cancer as compared with other occupations.

However, agricultural work is associated with a variety of health problems. Agricultural workers are at a high risk for particular cancers, respiratory diseases and injuries (Sullivan et al. 1992). Because of the remote location of much of this work, emergency health services are lacking, and agromedicine has been viewed as a vocation without high social status (see article “Agromedicine” and table 1). The work environment involves exposure to the physical hazards of weather, terrain, fires and machinery; toxicological hazards of pesticides, fertilizers and fuels; and health insults of dust. As shown in table 1, table 2, table 3, table 4, table 5, table 6 and table 7, agriculture is associated with a variety of health hazards. In these tables and the corresponding descriptions that follow, six categories of hazards are summarized: (1) respiratory, (2) dermatological, (3) toxic and neoplastic, (4) injury, (5) mechanical and thermal stress and (6) behavioural hazards. Each table also provides a summary of interventions to prevent or control the hazard.

Respiratory Hazards

Agricultural workers are subject to several pulmonary diseases related to exposures at work as shown in table 1. An excess of these diseases has been found in several countries..

Table 1. Respiratory hazards

Interventions: ventilation, dust suppression or containment, respirators, mould prevention, smoking cessation.

Sources: Merchant et al. 1986; Meridian Research, Inc. 1994; Sullivan et al. 1992;
Zejda, McDuffie et al. 1994.

Exacerbation of asthma by specific allergens and nonspecific causes has been associated with airborne dust. Several farm antigen exposures can trigger asthma, and they include pollen, storage mites and grain dust. Mucous membrane inflammation is a common reaction to airborne dust in individuals with allergic rhinitis or a history of atopy. Plant parts in grain dust appear to cause mechanical irritation to the eyes, but endotoxin and mycotoxin exposure may also be associated with the inflammation of the eyes, nasal passages and throat.

Chronic bronchitis is more common among farmers than among the general population. The majority of farmers with this illness have a history of exposure to grain dust or work in swine confinement buildings. It is believed that cigarette smoking is additive and a cause of this illness. In addition, acute bronchitis has been described in grain farmers, especially during grain harvest.

Hypersensitivity pneumonitis is caused by repeated antigen exposures from a variety of substances. Antigens include micro-organisms found in spoiled hay, grain and silage. This problem has also been seen among workers who clean out mushroom bed houses.

Organic dust toxic syndrome was originally associated with exposure to mouldy silage and was, thus, called silage unloader’s syndrome. A similar illness, called grain fever, is associated with exposure to stored grain dust. This syndrome occurs without prior sensitization, as is the case with hypersensitivity pneumonitis. The epidemiology of the syndrome is not well defined.

Farmers may be exposed to several different substances that can cause acute pulmonary responses. Nitrogen dioxide generated in silos can cause death among silo workers. Carbon monoxide generated by combustion sources, including space heaters and internal combustion engines, can cause death of agricultural workers exposed to high concentrations inside of buildings. In addition to toxic exposures, oxygen deficiency in confined spaces on farms is a continuing problem.

Many agricultural crops are causative agents for pulmonary diseases when they are processed. These include hypersensitivity pneumonitis caused by mouldy malt (from barley), paprika dust and coffee dust. Byssinosis is caused by cotton, flax and hemp dusts. Several natural products are also associated with occupational asthma when processed: vegetable gums, flax seed, castor bean, soybean, coffee bean, grain products, flour, orris root, papain and tobacco dust (Merchant et al. 1986; Meridian Research, Inc. 1994; Sullivan et al. 1992).

Dermatological Hazards

Farmers are exposed to several skin hazards, as shown table 2. The most common type of agriculture-related skin disease is irritant contact dermatitis. In addition, allergic contact dermatosis is a reaction to exposures to sensitizers including certain plants and pesticides. Other skin diseases include photo-contact, sun-induced, heat-induced, and arthropod-induced dermatoses.

Table 2. Dermatological hazards

Interventions: Integrated pest management, protective clothing, good sanitation, vaccination, insect control, barrier creams.

Sources: Estlander, Kanerva and Piirilä 1996; Meridian Research, Inc. 1994; Raffle et al. 1994; Sullivan et al. 1992.

The skin can be burned in several ways. Burns can result from dry fertilizer, which is hygroscopic and attracts moisture (Deere & Co. 1994). When on the skin, it can draw out moisture and cause skin burns. Liquid anhydrous ammonia is used for injecting nitrogen into the soil, where it expands into a gas and readily combines with moisture. If the liquid or gas contacts the body—especially the eyes, skin and respiratory tract—cell destruction and burns can occur, and permanent injury can result without immediate treatment.

Tobacco croppers and harvesters can experience green tobacco sickness when working with damp tobacco. Water from rain or dew on the tobacco leaves probably dissolves nicotine to facilitate its absorption through the skin. Green tobacco sickness is manifested with complaints of headache, pallor, nausea, vomiting and prostration following the worker’s contact with wet tobacco leaves. Other insults to the skin include arthropod and reptile stings and bites, and thorn punctures, which can carry diseases.

Toxic and Neoplastic Hazards

The potential for toxic substances exposure in agriculture is great, as can be seen table 3. Chemicals used in agriculture include fertilizers, pesticides (insecticides, fumigants and herbicides) and fuels. Human exposures to pesticides are widespread in developing countries as well as in the developed countries. The United States has registered more than 900 different pesticides with more than 25,000 brand names. About 65% of the registered uses of pesticides are for agriculture. They are primarily used to control insects and to reduce crop loss. Two-thirds (by weight) of the pesticides are herbicides. Pesticides may be applied to seed, soil, crops or the harvest, and they may be applied with spray equipment or crop dusters. After application, pesticide exposures can result from off-gassing, dispersion by the wind, or contact with the plants through skin or clothing. Dermal contact is the most common type of occupational exposure. A number of health effects have been associated with pesticide exposure. These include acute, chronic, carcinogenic, immunologic, neurotoxic and reproductive effects.

Table 3. Toxic and neoplastic hazards

Interventions: integrated pest management, respiratory and dermal protection, good pesticide application practices, safe re-entry time into fields after pesticide application, container labelling with safety procedures, carcinogen identification and elimination.

Sources: Connally et al. 1996; Hanrahan et al. 1996; Meridian Research, Inc. 1994; Pearce and Reif 1990; Popendorf and Donham 1991; Sullivan et al. 1992; Zejda, McDuffie and Dosman 1993.

Farmers experience a higher risk for some site-specific cancers. These include brain, stomach, lymphatic and haematopoietic, lip, prostrate and skin cancer. Solar and pesticide (especially herbicide) exposure have been related to higher cancer risks for farm populations (Meridian Research, Inc. 1994; Popendorf and Donham 1991; Sullivan et al. 1992).

Injury Hazards

Studies have consistently shown that agricultural workers are at increased risk of death due to injury. In the United States, a study of work-related fatalities for 1980 to 1989 reported rates in agricultural production of 22.9 deaths per 100,000 workers, as compared to 7.0 deaths per 100,000 for all workers. The average fatality rate for males and females, respectively, was 25.5 and 1.5 deaths per 100,000 workers. The leading causes of death in agricultural production were machinery and motor vehicles. Many studies report the tractor as the leading machine involved in fatalities, frequently from tractor rollovers. Other leading causes of death include electrocutions, caught in, flying objects, environmental causes and drowning. Age is an important risk factor related to agricultural fatalities for males. For example, the fatality rate for agricultural workers in the US over the age of 65 was over 50 per 100,000 workers, more than double the overall average (Meyers and Hard 1995) (see figure 1). Table 4 shows several injury hazard exposures, their consequences and recognized interventions.

Figure 1.  Agricultural workers fatality rates, US, 1980-89

Table 4. Injury hazards

Interventions: rollover protective structures, guards, good practices, safe electrical wiring, fire prevention, protective equipment, good housekeeping practices.

Sources: Deere & Co. 1994; Meridian Research, Inc. 1994; Meyers and Hard 1995.

A 1993 survey of farm injuries in the United States found the major injury sources to be livestock (18%), machinery (17%) and hand tools (11%). The most frequent injuries reported in this study were sprain and strain (26%), cut (18%) and fracture (15%). Males represented 95% of the injuries, while the highest concentration of injuries occurred among workers 30 to 39 years of age. Table 5 shows the source and nature of injury and the activity during injury for four major crop production categories. The National Safety Council estimated a US rate of 13.2 occupational injuries and illnesses per 100 crop production workers in 1992. More than half of these injures and illnesses resulted in an average of 39 days away from work. In contrast, the manufacturing and construction sectors had an injury and illness incidence rate of, respectively, 10.8 and 5.4 per 100 workers. In another study in the United States, investigators determined that 65% of all farm injuries required medical attention and that machinery other than tractors caused nearly half of the injuries that resulted in permanent disability (Meridian Research, Inc. 1994; Boxer, Burnett and Swanson 1995).

Table 5. Percentages of lost time injuries by source of injury, nature of injury, and activity for four types of agricultural operations, United States, 1993.

Source: Meyers 1997.

Mechanical and Thermal Stress Hazards

As discussed above, sprains and strains are a significant problem among agricultural workers, and as shown in table 6, agricultural workers are exposed to several mechanical and thermal stresses that result in injury. Many of these problems result from handling heavy loads, repetitive motion, poor posture and dynamic motion. In addition, agricultural vehicle operators are exposed to whole-body vibration. One study reported the prevalence of low-back pain to be 10% greater among tractor drivers.

Table 6. Mechanical and thermal stress hazards

Source: Meridian Research, Inc. 1994.

Noise-induced hearing loss is common among agricultural workers. One study reported that farmers more than 50 years of age have as much as 55% hearing loss. A study of rural students found that they have two times greater hearing loss than urban students.

Agricultural workers are exposed to temperature extremes. They may be exposed to hot, humid environments in work in the tropical and subtropical zones, and during the summer in the temperate zones. Heat stress and stroke are hazards under these conditions. Conversely, they may be exposed to extreme cold in the temperate zones in the winters and possible frostbite or death from hypothermia (Meridian Research, Inc. 1994).

Behavioural Hazards

Some aspects of farming can cause stress among farmers. As shown in table 7, these include isolation, risk taking, patriarchal attitudes, pesticide exposures, unstable economies and weather, and immobility. Problems associated with these circumstances include dysfunctional relationships, conflicts, substance abuse, home violence and suicide. Most suicides associated with depression on farms in North America involve victims who are married and are full-time farmers, and most use firearms to commit suicide. The suicides tend to happen during peak farming periods (Boxer, Burnett and Swanson 1995).

Table 7. Behavioural hazards

Sources: Boxer, Burnett and Swanson 1995; Davies 1995; Meridian Research, Inc. 1994; Parrón, Hernández and Villanueva 1996.

Migrant farm labourers are at high risk of tuberculosis, and where male workers predominate, sexually transmitted diseases are a problem. Female migrant workers experience problems of appropriate perinatal outcome, high infant mortality rates, and low occupational risk perceptions. A broad range of behavioural issues is currently being investigated among migrant workers, including child abuse and neglect, domestic violence, substance abuse, mental disorders and stress-related conditions (ILO 1994).

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Since animal husbandry and crop production began, agriculture and medicine have been interrelated. A healthy farm or livestock operation requires healthy workers. Famine, drought, or pestilence can overwhelm the well-being of all of the interrelated species on the farm; especially in developing countries that depend on agriculture for survival. In colonial times plantation-owners had to be aware of hygienic measures to protect their plants, animals and human workers. At present, examples of agromedical teamwork include: integrated pest management (an ecological approach to pests); tuberculosis (TB) prevention and control (livestock, dairy products and workers); and agricultural engineering (to reduce trauma and farmer’s lung). Agriculture and medicine succeed when they work together as one.

Definitions

The following terms are used interchangeably, but there are noteworthy connotations:

• Agricultural medicine refers to the subdivision of public health and/or occupational medicine included in the training and practice of health professionals.

• Agromedicine is a term coined in the 1950s to emphasize interdisciplinary, programmatic approaches which give a greater role for the agricultural professional based upon the equal partnership of the two disciplines (medicine and agriculture).

In recent years, the definition of agricultural medicine as a subspeciality of occupational/environmental medicine located on the health sciences campus has been challenged to develop a broader definition of agromedicine as a process of linking agricultural and health resources of a state or a region in a partnership dedicated to public service, along the lines of the original land-grant university model.

The essential unity of biological science is well known to plant chemists (nutrition), animal chemists (nutrition) and human chemists (nutrition); the areas of overlap and integration go beyond the boundaries of narrowly defined specialization.

Content areas

Agromedicine has focused on three core areas:

1. traumatic injury
2. pulmonary exposures
3. agrichemical injury.

Other content areas, including zoonoses, rural health services and other community services, food safety (e.g., the relationship between nutrition and cancer), health education and environmental protection, have received secondary emphasis. Other initiatives relate to biotechnology, the challenge of population growth and sustainable agriculture.

Each core area is emphasized in university training and research programmes depending on faculty expertise, grants and funding initiatives, extension needs, commodity producers’ or corporate requests for consultation and networks of inter-university cooperation. For example, traumatic injury skills may be supported by a faculty in agricultural engineering leading to a degree in that branch of agricultural science; farmer’s lung will be covered in a pulmonary medicine rotation in a residency in occupational medicine (post-graduate specialization residency) or in preventive medicine (leading to a master’s or doctorate in public health); an inter-university food safety programme may link the veterinary discipline, the food science discipline and the infectious disease medical speciality. Table 1 compares two types of programmes.

Table 1. Comparison of two types of agromedicine programmes

In the United States, a number of states have established agromedicine programmes. Alabama, California, Colorado, Georgia, Iowa, Kansas, Kentucky, Minnesota, Mississippi, Nebraska, New York, Oregon, Pennsylvania, South Carolina, Virginia and Wisconsin have active programmes. Other states have programmes which do not use the terms agromedicine or agricultural medicine or which are at early stages of development. These include Michigan, Florida and Texas. Saskatchewan, Canada, also has an active agromedicine programme.

Conclusion

In addition to collaboration across disciplines in so-called basic science, communities need greater coordination of agricultural expertise and medical expertise. Dedicated localized teamwork is required to implement a preventive, educational approach that delivers the best science and the best outreach that a state-funded university system can provide to its citizens.

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