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Submitted to: Manual of Techniques in Insect Pathology
Publication Type: Book / Chapter Publication Acceptance Date: 3/1/2012 Publication Date: 8/1/2012 Citation: Siegel, J.P. 2012. Testing the pathogenicity and infectivity of entomopathogens to mammals. Manual of Techniques in Insect Pathology. 441-450. Interpretive Summary: The purpose of this book chapter is to provide both a brief overview of the philosophy of mammalian safety testing of insect pathogens as well as to provide 4 protocols for preliminary tests of a potential candidate organism. Mammalian safety screens are a subset of a larger grouping of tests that assess the effects of a microbial pest control agent (MPCA) on nontarget organisms (NTO). Non-target organisms include plants, fish, beneficial arthropods, birds and mammals. Initially, it is important to come up with a standard definition of the term infection, because infection or infectivity is an unacceptable outcome in these experiments. The definition of infection used in this chapter links recovery of the test organism to tissue damage. Simple recovery of an organism does not mean that it is infectious, especially when it is injected at a very high dose. It is possible for some microorganisms to persist in the test animal for weeks after administration without multiplying. The tests presented in the chapter are short term or acute tests, and do not last longer than 28 days. In contrast, tests that examine whether a chemical can cause cancer may last as long as two years. The first test, acute oral, lasts for 21 days after a single administration of a large dose by mouth. The second test applies the test organism to abraded skin and lasts 14 days. The third test involves inhalation and lasts 21 days and the final test, which is the most invasive, injects the test organism into the animal’s peritoneal cavity. These animals are followed for 28 days and are monitored for illness. The basic challenge of safety testing is determining when a candidate is reasonably safe, and an organism that successfully passes these four tests is a good candidate for further development and more stringent testing. Technical Abstract: The purpose of this chapter is to provide a brief overview of mammalian safety testing, as well as short term testing protocols that can help determine if a candidate organism is suitable for more detailed study. Although it may seem a matter of common sense that known vertebrate pathogens will not be used in agriculture or in vector control, there are regulatory mechanisms in place that require that potential insect control agents be evaluated. Mammalian safety screens are a subset of a larger grouping of tests that assess the effects of a microbial pest control agent (MPCA) on nontarget organisms (NTO). Non-target organisms include plants, fish, beneficial arthropods, birds and mammals. Ultimately, NTO testing can be viewed as attempts to manipulate a candidate organism into doing something it would not do in nature, either by providing access to hosts outside its natural range or by varying both the dose and route of exposure in order to produce infection and/or mortality. These tests are conducted with the expectation that the infectivity and the majority of the toxicity tests will be negative, because of the specificity of entomopathogens to arthropods. While it is always possible to kill an animal if the dose is high enough, through suffocation, embolism, or blockage of the gastrointestinal tract, these results have little relevance to the real world and the test results must be judged in the context of the experimental protocol. An adverse outcome in any one screen may not be grounds for automatic rejection but further tests will probably be conducted to quantify the effect. The goal of this chapter is to briefly summarize the history and philosophy behind these tests and then present a series of single exposure short-term tests that can be used to assess the mammalian safety of a candidate organism. The tests presented are based on the registration requirements of the United States Environmental Protection Agency, subdivision M (Anonymous, 1988) and guidelines published by the World Health Organization (WHO) (Anonymous, 1981). These four screens may serve as a starting point for the registration of an entomopathogen or a point of comparison for an existing protocol. The first test, acute oral, lasts for 21 days after a single administration of a large dose by mouth. The second test applies the test organism to abraded skin and lasts 14 days. The third test involves inhalation and lasts 21 days and the final test, which is the most invasive, injects the test organism into the animal’s peritoneal cavity. These animals are followed for 28 days and are monitored for illness. Ultimately, the test results will enable the researcher to determine the hazard posed by the candidate organism, and if the hazard is acceptable more stringent tests should be conducted that are in compliance with the registration requirements for the registrants’ market. |
