* Natural Resource Economist/Consultant, EMBRAPA/PROMOAGRO, Brazilian Center for Agricultural Research in the Pantanal (CPAP/EMBRAPA), Rua 21 de Setembro, 1.880, CX Postal 109, CEP 79.320-900, Corumbà, MS, Brazil. Fax: 55-67-231-1011. E-mail: Loureiro@cpap.embrapa.br.
2. Informational needs
3. Illustration: T. Evansi in the Brazilian Pantanal
Whether and how to treat animal trypanosomosis can be considered economic decisions laden with risk and uncertainty. Animal trypanosomosis affects the health and productivity of livestock. Presumably, people raise livestock for, largely, economic reasons. Providing information to decision-makers regarding alternative strategies to alleviate risk or mitigate the economic impact of animal trypanosomosis is complementary to and dependent on the rich biological research on the subject. Here, the general types of information necessary to make a reasonable determination of the potential impact of this family of diseases on livestock and the alternatives for mitigating their effects are reviewed. However, the manipulation of the relevant information will vary substantially depending on the needs of the particular situation. As a result, the impact of T. evansi on the Brazilian Pantanal is used to illustrate the techniques employed and to give a sense of how biological information is combined with economic information to aid in risky decision-making.
Both economic and biological information are necessary to assess the economic effects and treatment alternatives for trypanosomes. The quality of economic analyses of livestock diseases is closely linked to the quality of the biological information upon which they are based. In order to assess the potential or anticipated economic impact of livestock diseases on human beings, we first must understand the expected impact of the disease on the livestock.
2.1. Biological information
In terms of biological information we need to know:
(1) the risk of an individual animal contracting the disease over a specific period of time;
(2) the life cycle of the disease in the infected animal; and
(3) the effect of alternative treatments on the disease and on the animal.
More specifically, analyses will proceed differently if the disease tends to afflict young or old animals more than "working age" animals, occurs seasonally, under certain conditions, or in specific locations, kills or, alternatively, physically debilitates the animal and over what time period, influences animal productivity in terms of reproduction, meat or milk production, or tends to build resistance to some treatments over others. In addition, the duration of prophylaxis or therapeutic effect resulting from treatment and the effect on animal health of the treatment administered at different periods within the life cycle of the disease influence the analysis.
2.2 Economic information
The control strategy that saves the most animals is not necessarily the most desirable strategy from an economic perspective. If saving or treating an animal is more costly than its value to the decision-maker, then the animal should not be saved economically speaking. In order to determine what is and is not an economically feasible strategy, we need to know:
(1) who is the decision-maker (e.g., government, veterinarian, large rancher, small rancher);
(2) what is his attitude toward risk with regard to this decision (e.g., risk averse, risk neutral);
(3) the price of animals and animal products by category and magnitude potentially effected;
(4) the full costs of control alternatives including veterinary, animal collection, treatment and diagnostic costs and anticipated animal losses.
Depending upon the identity of the decision-maker different strategies may become preferable. For example, some treatment strategies may demonstrate significant economies of scale, providing greater incentives to adoption on the part of large ranches than those with fewer animals. Government decision-makers are more likely to be concerned with the regional impact of the disease than individual ranchers are. Thus, potential positive effects of livestock diseases on veterinarians, drug companies, and alternative meat producers or negative effects on water supplies, meat/milk supplies, wildlife, or general animal welfare, make some strategies more or less attractive to governments than they are to ranchers.
Knowledge of the decision-maker's attitude toward risk provides a way to determine whether "an ounce of prevention equals a pound of cure." For a risk-neutral individual, a dollar of prevention is equal to a dollar of cure. For a risk-averse decision-maker, a dollar of prevention is worth more than a dollar of cure. For many human health related issues, decision-makers are risk-averse, preferring vaccination programmes, for example, over curative medications and treatments.
The total number of animals potentially affected and their relative prices gives an indication of the costs of the disease in anticipated animal losses. Depending on whether the animal is used for meat, milk or work, the impact of the disease may be distinct economically. The age of affected animals relative to their market price profile and the impact of the disease gives an indication of whether animal value is equivalent to its replacement cost or if it should be discounted to reflect depreciation of a capital asset.
Using relevant available economic and biological information the potential impact of animal trypanosomosis can be calculated for various stakeholders and the risk-laden decision process can be simulated. This information, in conjunction with detailed treatment information, provides the decision-maker with a number of potential treatment strategies to mitigate the effect of the disease. The case of T. evansi in the Brazilian Pantanal serves for illustration.
In the case of the Pantanal, biological and economic variables are used to estimate the impact of T. evansi across three distinct dimensions: regional ranching sector; individual ranch (by ranch size); and regional policy (using economic instruments to affect animal welfare). These variables can be divided into ranch profile variables (e.g. ranch size, number of cattle, number of horses, number of ranches, animal prices), disease profile variables (e.g. risk of infection, effect of disease), and treatment profile variables (e.g. costs of drugs, needles, syringes, collection of animals, veterinary and diagnostic costs, and treatment protocol).
3.1 Ranch Profile Variables
We estimate that there are 4, 104 total agricultural properties, 49, 000 horses, and over 3 million cattle in the Pantanal. The estimated mean price of horses is US$375. We divide ranches along traditional lines into 4 size categories: <3, 600 ha; 3, 601-7, 200 ha; 7, 201-14, 400; and >14, 401 ha. The number of horses by property size is calculated based on the observed proportion of "work animals" per head of cattle in each of the 4 property sizes (Cadavid Garcia, 1986).
3.2 Disease Profile Variables
The annual risk of infection, for the region and the individual farm, of 13.2% is gleaned from the composite index of disease prevalence found in one of the subregions of the Pantanal (Franke et al., 1994). In the Pantanal, T. evansi results in certain death of equine species within a week to ten days of infection (Silva et al., 1995). Silva et al. (1995) found that 90% of the cases of T. evansi in the Pantanal occurred during the high vector and high animal stress rainy season, allowing seasonal treatment applications to be meaningfully explored. Animal productivity losses are total in the absence of treatment.
3.3. Treatment Profile Variables
The cost of collecting animals for treatment or diagnosis is calculated as the cost of two ranch employees for one day for each 130 animals or US$7.32. Ranchers must either be veterinarians themselves or hire one to diagnose their animals in the case of a suspected outbreak. Costs incurred by the rancher include transportation, diagnostic testing, lab work, and visitation charges (estimated total US$175 per visit). Treatment costs depend upon the protocol and effectiveness for each drug. Here various scenarios are explored for Diminazine aceturate-based and Isometamidium chloride-based treatment strategies. Estimated variables include the cost of the drug itself (US$9.42 (Diminazine), US$3.00 (Isometamidium)), needles and syringes (US$0.52), and the requisite frequency and type of treatment (curative or preventive).
Results indicate that untreated T. evansi will have an anticipated impact of about US$2.4 million per year on the Pantanal region. More than 40% of the impact falls to the largest Pantanal ranches. The implementation of an annual curative strategy (Diminazine aceturate) is considered the most economically beneficial at the regional and individual level across ranch size. This strategy results in an annual expected net benefit to the region of over US$2 million with 43% of the benefits falling to the largest ranches. A seasonal curative strategy and a preventive strategy (Isometamidium chloride) are also found to be economically justifiable, but are less attractive on economic grounds than the annual curative strategy.
Animal Trypanosomosis has profound social, economic and biological implications for effected regions. Social and biological scientists engaged in this area of research have fertile ground from which useful and mutually beneficial collaborative efforts can and should proceed. Both types of information are necessary and neither is sufficient. Biological information on its own cannot help people determine the appropriate strategy for mitigating the impact of animal diseases. Economic analyses are worthless without high quality biological information. A simple case of the impact of T. evansi on the Brazilian Pantanal has served to illustrate how the integration of biological information with economic risk-laden decision analysis can provide useful information to a variety of potential stakeholders. It is from this integrated perspective that I hope to encourage further collaborative efforts among us to better serve our constituencies.
Cadavid Garcia, E.A., 1986. Estudo Tecnico-Economico da Pecuaria Bovina de Corte do Pantanal Mato-Grossense. Corumba, EMBRAPA, CPAP.
Franke C.R., Greiner M., and Mehlitz D., 1994. Investigations on naturally occurring Trypanosoma evansi infections in horses, cattle, dogs and capybaras (Hydrochaeris hydrochaeris) in Pantanal de Pocone (Mato Grosso, Brazil). Acta Trop., 58: 159-169.
Silva, R.A.M.S., Barros, A.T.M., and Herrera, H.M., 1995. Foyers trypanosomiens dus à Trypanosoma evansi dans le Pantanal, Brésil. Une approche préliminaire sur les facteurs de risque. Revue Elev. Méd. vét. Pays trop., 48 (4): 315-319.