The main health hazards relating to work in agriculture include: zoonotic diseases, pesticide poisoning, accidents, and respiratory diseases due to organic and vegetable dusts. Farmers have the highest rate of skin disorders, including skin cancer resulting from too much sun and eczema from handling detergents and chemicals. They inhale clouds of dust, animal dender, even deadly fumes. Farmer's lung is an allergic reaction to mouldy hay; silo-filler's disease kills farmers unaware of the buildup of nitrogen oxides produced by fermenting forage; milker's knee is arthritis caused by years of squatting.
On large state and cooperative farms making wide use of agricultural machinery, the main health concern lies with machine operators. Many suffer hearing loss from the clatter of machinery. Tractor rollovers are the biggest killer on farms. Although the problem of accidents in agriculture is not a new one, in a number of countries the number of accidents is growing in direct proportion to the increase in the use of agricultural machinery. On the other hand, in a small-farm economy, with its low level of mechanization, each individual performs a variety of different jobs, so that the work has no clearly distinguishable occupational character and is heavy and exhausting.
Health conditions in agriculture depend on the nature and level of development of agricultural production. However, regardless of the size or sophistication of the farm, a distinctive feature of agriculture is its seasonal nature and the urgency of different forms of field work depending on the character of the crop under cultivation. As a result, one of the main tenets of occupational physiology - a regulated working day - is often violated. Long or irregular hours of work lead to over-exhaustion, to a reduction in productivity and, in a number of cases, to fatigue followed by a reduction in the immune reaction to infection.
Domestic animals are a common source of infection and infestation. At the present time, the transmission of brucellosis, tuberculosis and other diseases is recorded in many countries, and in a number of places also tularaemia. Throughout the world, tetanus and other diseases connected with agriculture are encountered.
The widespread use of pesticides has led in many countries to cases of intoxication, both acute and chronic, though the number of acute poisonings has not been very great. Low-level pesticide exposure can produce symptoms similar to colds or stomach upsets -- hence there is an underreporting of poisoning incidents. There is speculation that the halving of male fertility since 1940 and the growth of allergy-related diseases are both linked to pesticide intoxication.
A large number of workers are employed in agriculture and in the processing of agricultural products; exposure to vegetable and other organic dusts is widespread. Several occupational diseases due to such exposure have been described, and some are included in the statutory lists of notifiable diseases in certain countries, for example: byssinosis, farmers' lung, bagassosis, and occupational asthma. Many dusts and their health effects have not been systematically investigated. Exposure to dusts of grain, rice, cocoa, coconut fibres, tea, kapok, tobacco and wood is common in the countries where these products are grown; and there is evidence that obstructive respiratory disease and asthma may result. Respiratory disability has been observed among villagers exposed since childhood to flax dusts at home.
Although farm workers comprise only about 4.4% of the work force in the USA, about 16% of total occupational deaths and 9% of all occupational injures occur in this group. With the increasing use of agricultural machinery occupational injuries are becoming more frequent in developing countries; and in some industrialized countries the occupational accident rate for agriculture now ranks third, after those for mining and building. In some countries field surveys among spraymen exposed to poisoning in up to 40% of them during a spraying period. Up to 90% of textile workers exposed to cotton, flax or hemp dust have been affected by byssinosis. Even at low dust concentrations and duration of exposure, dust adversely affects 20% to 40% of textile workers; permanent pulmonary disability has been found in up to 20% of the workers affected.
California grows half the fruits and vegetables in the United States. Its farmers handle a lot of dangerous pesticides. One of the chemicals, parathion, has been used heavily on cotton and food crops. Parathion has killed more than fifty farm workers who have handled it. By drifting through the air or collecting in groundwater, it has poisoned many more people, with less-than-fatal, but nonetheless serious consequences. The risks of pesticides - on and off the farm, to children and to adults - have lead many farmers in the San Joaquin valley to turn to organic farming and to biological control.