Treatment strategies for sheep scab: An economic model of farmer behaviour.

Ovine psoroptic mange (sheep scab) is a debilitating and damaging condition caused by a hypersensitivity reaction to the faecal material of the parasitic mite Psoroptes ovis. Farmers incur costs from the use of prophylactic acaricides and, if their sheep become infected, they incur the costs of therapeutic treatment plus the economic loss from reduced stock growth, lower reproductive rate, wool loss and hide damage. The unwillingness of farmers to use routine prophylactic treatment has been cited as a primary cause of the growing incidence of sheep scab in the United Kingdom (UK) since the disease was deregulated in 1992. However, if farmers behave rationally from an economic perspective, the optimum strategy that they should adopt will depend on the risk of infection and the relative costs of prophylactic versus therapeutic treatment, plus potential losses. This calculation is also complicated by the fact that the risk of infection is increased if neighbours have scab and reduced if neighbours treat prophylactically. Hence, for any farmer, the risk of infection and optimum approach to treatment is also contingent on the behaviour of neighbours, particularly when common grazing is used. Here, the relative economic costs of different prophylactic treatment strategies are calculated for upland and lowland farmers and a game theory model is used to evaluate the relative costs for a farmer and his/her neighbour under different risk scenarios. The analysis shows that prophylaxis with organophosphate (OP) dipping is a cost effective strategy, but only for upland farmers where the risk of infection is high. In all other circumstances prophylaxis is not cost effective relative to reliance on reactive (therapeutic) treatment. Hence, farmers adopting a reactive treatment policy only, are behaving in an economically rational manner. Prophylaxis and cooperation only become economically rational if the risk of scab infection is considerably higher than the current national average, or the cost of treatment is lower. Should policy makers wish to reduce the national prevalence of scab, economic incentives such as subsidising the cost of acaricides or rigorously applied financial penalties, would be required to make prophylactic treatment economically appealing to individual farmers. However, such options incur their own infrastructure and implementation costs for central government.

Pesticide sales in low-income, minority neighborhoods.

The US EPA has phased-out residential use of two organophosphate pesticides commonly used to control cockroaches-retail sales of chlorpyrifos were scheduled to end on 12/31/01, and diazinon on 12/31/02. In light of recent findings highlighting the associations between pests, pesticides and health, we surveyed stores in low-income, minority neighborhoods in New York City to determine whether the phase-outs have been effective and to assess the availability of alternatives to spray pesticides. In summer 2002, when sales of chlorpyrifos were illegal and diazinon still legal, we surveyed 106 stores selling pesticides. Four percent sold products containing chlorpyrifos and 40 percent sold products containing diazinon. One year later, when sales of both pesticides were to have ended, we surveyed 109 stores selling pesticides in the same neighborhoods and found chlorpyrifos in only one store and diazinon in 18 percent of stores, including 80 percent of supermarkets surveyed. At least one form of lower toxicity pesticides, including gels, bait stations and boric acid was available in 69 percent of stores in 2002. However sprays were most widely available, found in 94 percent of stores in 2002 and less expensive than lower toxicity baits and gels. In a separate survey of storekeeper recommendations conducted in 2002, storekeepers recommended lower toxicity pesticides as the best way to control cockroaches 79% of the time. The EPA's phase-outs have nearly eliminated sales of chlorpyrifos, but the diazinon phase-out appears to be less effective.