Bioscope ‘07

by  Dr. Barbara Price

Biosecurity, Infectious Disease Modeling and GIS

          As more scientists become familiar with the advantages of using GIS to track the spread of infectious diseases and see their patterns, the number of GIS-based programs for surveillance and epidemiology has increased. Concerns about biosecurity have given an additional spurt to these programs. The GIS part is the easy part; the real keys are the assumptions involved in modeling the disease and its spread. Public health professionals can use these models to develop policies, which can protect us all, for natural occurrences, emerging diseases, pandemics and biological and terrorist attacks.

          Distinguishing between normal or endemic occurrences of disease requires understanding endemic diseases, their infectivity, and susceptibility of the predominant population; i.e., the SEIR (Susceptible, Exposed, Infectious, Recovered) model. When is an outbreak above the endemic background? The answers depend on the pathogenicity and transmissibility of the agent and on the population genetics, susceptibility, and available public health controls and support.

          Recent papers discussed the use of an "epidemic threshold parameter", the assumption that one infected individual that produces more than one secondary infection decides whether an outbreak becomes an epidemic. Studying the individual transmissions is not the same as studying the "transmission network", which involves the community, including possible existing public health practices and policies. Extreme examples include a very high transmissibility via respiratory fluids, such as the Norovirus on cruise ships and SARS, both of which are quickly limited using public health controls, such as washing affected surfaces and isolation. In those cases, population susceptibility and individual transmission are generally not as important as the public health controls.

          Studying the population genetics along with intrinsic infectivity, pathogenicity and immune properties of the infectious agent is critical, but also can be considered dual-use. Without these studies, we cannot make progress against diseases.

Food Security, More Than Just Pet Food

          The recent recall of contaminated pet food raise many questions going beyond pet food. Where does our food come from and are we sure it is safe? The FDA in the US does not have funding or capacity for all the testing needed.

          Melamine is not likely to be the only contaminant in the affected pet food. Chronic feeding tests of rats and dogs (30,000 ppm) have not indicated significant health changes, except for crystalluria (urine containing melamine phosphate crystals) and extra urine production (diuresis) in dogs, but no abnormalities in tissues at autopsy after one year. SAX lists an acute oral LD₅₀ for rats of 3.1 g/kg. If melamine behaves similarly in dogs, a 15 lb dog would need to consume over 21 g, and the chunks and gravy pouches in question are usually 85 g total.

          Aminopterin, once investigated as a leukemia drug, is also used as a rodenticide. It interferes with embryonic development and fertility, and sterilizes rats. Although 941 citations in Toxline do not indicate that aminopterin affects the kidneys or urinary function, perhaps further studies may show that it does.

For the Professional in Government and Industry with an interest in Nuclear, Biological and Chemical Defense, Disarmament and Verification; Emergency and Disaster Medical Planning; Industrial Health and Safety; and Environmental Protection