Animal Reservoir

This article provides an overview of the emerging field of mathematical modeling in preharvest food safety. We describe the steps involved in developing mathematical models, different types of models, and their multiple applications. The introduction to modeling is followed by several sections that introduce the most common modeling approaches used in preharvest systems. We finish the chapter by outlining potential future directions for the field.

Mathematical models of infectious diseases are a valuable tool in understanding the mechanisms and patterns of disease transmission. It is, however, a difficult subject to teach, requiring both mathematical expertise and extensive subject-matter knowledge of a variety of disease systems. In this article, we explore several uses of zombie epidemics to make mathematical modeling and infectious disease epidemiology more accessible to public health professionals, students, and the general public. We further introduce a web-based simulation, White Zed (http://cartwrig.ht/apps/whitezed/), that can be deployed in classrooms to allow students to explore models before implementing them. In our experience, zombie epidemics are familiar, approachable, flexible, and an ideal way to introduce basic concepts of infectious disease epidemiology.

The kinetoplastid infections are transmitted by insect vectors, and the three major kinetoplastid infections of humans, human African trypanosomiasis (HAT), Chagas disease, and leishmaniasis, kill approximately 70,000 people annually, making them among the most lethal neglected tropical diseases (NTDs). HAT, also known as sleeping sickness, is caused by two different species of trypanosomes. Trypanosoma brucei gambiense is the cause in West Africa, while T. b. rhodesiense occurs in East Africa. It results from the bite of tsetses of the genus Glossina. Control of West African HAT relies largely on case detection and treatment as well as vector control, while fighting East African HAT relies on control in animal reservoirs and vector control. Chagas disease, also known as American trypanosomiasis, is caused by T. cruzi, which has the ability to invade host cells and replicate as amastigotes. The infection is transmitted by kissing bugs, primarily of the genus Triatoma. Control of Chagas disease in the Southern Cone has been highly effective through indoor spraying that targets the vector, T. infestans. Leishmaniasis is transmitted by the bite of a sandfly. Cutaneous leishmaniasis (CL) is a disfiguring, pizza-like lesion, which often self-heals but can leave a scar. The scar is often deeply stigmatizing for women in developing countries. Visceral leishmaniasis (VL), or kala-azar, produces a febrile wasting syndrome with signs and symptoms that resemble leukemia. Drugs containing antimony are still widely used for the treatment of CL and VL, but are toxic and difficult to administer.

The name of Ali Maow Maalin deserves to be just as familiar to microbiology students as that of James Phipps, for it was Maalin, a 23-year-old Somalian cook, who in 1977 became the world’s last naturally acquired case of smallpox. Some time over the next few years, hopefully, another name, that of the last person on Earth to contract paralytic polio caused by wild poliovirus, will join the historic duo. Even today, the book from the 1997 conference, The Eradication of Infectious Diseases, stands as a major dossier on the realities of global and regional disease eradication efforts. Even the most formidable obstacles, such as the existence of an animal reservoir, can sometimes be overcome. The persistence of viable organisms in patients following recovery is one phenomenon that clearly can jeopardize wide-scale elimination. One of the principal lessons to emerge from previous programs of disease extermination is the importance of thoroughly understanding the natural history of particular pathogens. Then, suddenly, new outbreaks occurred in Brazil and elsewhere, leading to the discovery that the virus was carried not only by Aedes agypti, but also by mosquitoes living in the forest canopy. The World Health Organization's yaws campaign, one of its first initiatives in disease control, provides another lesson. The more radical step of exterminating pathogens entirely is bound to pose sharper dilemmas in relation to biodiversity as others become candidates for extinction.

The kinetoplastid infections constitute a group of three major human protozoan infections caused by single-celled parasites with a flagellum and an unusual DNA-containing cell organelle known as the kinetoplastid. Together, the three major kinetoplastid infections of humans, human African trypanosomiasis (HAT), Chagas’ disease, and leishmaniasis, kill an approximately 150,000 people annually, making them among the most lethal neglected tropical diseases (NTDs). West African HAT typically occurs around rivers, especially in areas of dense vegetation where tsetses of the Glossina palpalis group are abundant. The chapter shows how the fact that Rhodesian HAT is primarily a zoonosis, i.e., a disease transmitted from animals to humans, has important implications for controlling epidemics of this disease. In addition to melarsoprol, there are two other drugs, pentamidine and suramin, still in widespread use for the earlier stage of HAT. The treatment of the chronic complications of Chagas’ disease requires complex modalities. There are no simple preventive chemotherapy approaches for the control of Chagas’ disease, nor is it practical to apply wide-scale case detection and management with antitrypanosomal drugs such as what occurred with the pentamidization campaigns against HAT launched in the 20th century. Approximately 12 million people are infected with Leishmania parasites. There are two major forms of the disease—visceral leishmaniasis, and cutaneous leishmaniasis (CL). Both CL and VL are treatable infections, but many of the drugs used produce severe toxicities, and in many cases they are not available.

All of us—consumers, food handlers, and food safety professionals— are subject to the “old habits” syndrome. But we cannot afford to be complacent. To ensure the safety of our food and water supply, we must always look to our past experiences to teach us the best and safest ways to produce, prepare, and store food. Allowing a hot dish to cool on the countertop is no longer advisable; in fact, it can be downright dangerous. This chapter discusses the hazards of continuing old habits for thawing and cooking frozen food with a few illustrations. On March 31, 1986, Oklahoma’s four schools reported an where victims variously reported experiencing nausea, vomiting, cramps, or fever. Many suffered from a combination of two or more symptoms. In all, more than 200 people were stricken with Salmonella food poisoning courtesy of the chicken. In another incident on March 18, 1993, the Cleveland City Health Department began receiving telephone calls from individuals stricken with food poisoning after consuming sandwiches from Danny's Deli. The Ohio Department of Health, which analyzed the suspect meat, reported that it contained a high concentration of Clostridium perfringens, a bacterium known to cause food poisoning and often associated with this type of outbreak. These and other reports in the chapter teach us that we must always look to our past experiences to teach us the best and safest ways to produce, prepare, and store food.

Since the early 1950s, antimicrobials have been used in companion, sport, and food animals to treat bacterial infections and to control or prevent their spread throughout populations. While it seems clear from even the most conservative industry estimates that the total amount of antimicrobials administered to animals in the United States is not insignificant relative to use in human medicine, the exact quantity administered annually remains unknown. In the United States, antimicrobial resistance surveillance is conducted through the National Antimicrobial Resistance Monitoring System-Enteric Bacteria (NARMS). NARMS monitors changes in antimicrobial drug susceptibilities of selected bacteria in food animals, humans, and retail meats in relation to antimicrobial agents of importance in human and food animal medicine. Indicator species monitored by NARMS include strains of Campylobacter, Escherichia coli, Enterococcus, Listeria, Salmonella, and Vibrio. The only official data on antimicrobial use in animals available to the public are annual surveys conducted by the National Animal Health Monitoring System (NAHMS) of U.S. Department of Agriculture (USDA). Alliance for the Prudent Use of Antibiotics (APUA) established an Advisory Committee on Animal Antimicrobial Use Data Collection in the United States in the spring of 2002 in order to address methodological issues surrounding domestic food animal antimicrobial use surveillance. Citing concerns for food safety, some multinational food-industry corporations have also become involved in issues relating to antimicrobial use in food animals in recent years.