Tang X-H, Gudas LJ: Retinoids, retinoic acid receptors, and cancer, Annu Rev Pathol 6:345, 2011. [A review of the role of retinoids in cancer, with a focus on solid tumors.] van der Klaauw AA, Farooqi IS: The hunger genes: pathways to obesity, Cell 161:119, 2015. [A succinct review of the afferent pathways to obesity.]
Wilson J, Enriori PJ: A talk between fat tissue, gut, pancreas, and brain to control body weight, Mol Cell Endocrinol 418:108, 2015. [Excellent discussion of the various afferent pathways in obesity.] http://ebooksmedicine.net studentconsult.com
General Pathology of Infectious Diseases
Categories of Infectious Agents
Routes of Entry of Microbes
Spread and Dissemination of Microbes Within the Body
Transmission of Microbes
Mechanisms of Viral Injury
Mechanisms of Bacterial Injury
Injurious Effects of Host Immune Responses
Humans are prey to thousands of infectious agents ranging from submicroscopic viruses to several meters long tape worms. This chapter reviews the general principles of the pathogenesis of infectious disease and describes the characteristic histopathologic changes caused by different types of microbes. Infections that involve specific organs are discussed in other chapters of this book.
Infectious diseases are an important health problem in the United States and worldwide despite the availability of effective vaccines and antibiotics for many types of infections. Influenza and pneumonia combined are the eighth leading cause of death in the United States. In low-income countries, limited access to healthcare, unsanitary living conditions, and malnutrition contribute to a massive burden of infectious diseases. Lower-respiratory infections, HIV/AIDS, and diarrheal diseases are the top three causes of death in developing countries, and malaria and tuberculosis are among the top ten. Infectious diseases are particularly important causes of death among children, older adults, individuals with chronic debilitating diseases and inherited or acquired immunodeficiency states (e.g., AIDS), and in patients receiving immunosuppressive drugs.
Infectious agents belong to a wide range of classes and vary greatly in size, ranging from prion protein aggregates of under 20 nm to tapeworms 10 meters in length (
Table 9.1
Prions are composed of abnormal forms of a host protein termed prion protein (PrP). These agents cause transmissible spongiform encephalopathies, including kuru (associated with human cannibalism), hereditary or sporadic Creutzfeldt-Jakob disease (CJD), bovine spongiform encephalopathy (BSE) (better known as mad cow disease), and variant Creutzfeldt-Jakob disease (vCJD) (probably transmitted to humans through consumption of meat from BSE-infected cattle). PrP is found normally in neurons. Diseases occur when the PrP undergoes a conformational change that confers resistance to proteases. The protease-resistant PrP promotes conversion of the normal protease-sensitive PrP to the abnormal form, explaining the transmissable nature of these diseases. CJD can be transmitted from person to person iatrogenically, by surgery, organ transplantation, or blood transfusion. These diseases are discussed in detail in Chapter 23.