LECTURE 23 2 topics: 1. Immunology 2. Emerging Pathogens Benefits of the Normal Flora: 1. Protect us from colonization by other bacteria and fungi (competitive exclusion). 2. Many synthesize vitamins, e.g. E. coli make Vitamin K and some B vitamins. 3. They can stimulate the development of certain tissues. 4. Nitrogen fixation in intestines of vegetarians Probiotics - inoculation with normal flora to prevent infection or to recover from antibiotic therapy e.g. Yogurt - intestinal flora Many baby animals are now treated with normal flora to prevent colonization by pathogens - chickens are treated to prevent colonization by antibiotic-resistant Salmonella spp. Review other barriers to infection See Figure 15.3 and read pages 372-376. Fig. 15.3 Barriers to infection Other defenses: The Inflammatory Response removes invaders from an injured area via one or more of the following: 1. dilation of capillaries (allows more phagocytes to get to the invaders), 2. release of chemotactic factors (attracts phagocytes to the area), 3. increased permeability of capillary walls (allows phagocytes to get into damaged tissues), clot formation (blocks further invasion in large wounds) See figure 15.10 The Immune Response. just enough immunology so that we can understand the basics of how the immune system responds to microbes and viruses. some concepts and terminology: Antigens = molecules to which the immune system responds. Common antigens are found on the outside of cells (or viruses). e.g.: polysaccharide portion of the LPS of gram- bacteria. Other antigens include pili, flagella, porin proteins and exotoxins. Outer proteins of viruses are also good antigens. Almost any protein greater than 1000 daltons in size can be an antigen (but most. 10,000 daltons)
Antigens (from antibody generator) = substances that elicit an immune response Antibodies (Immunoglobins) Made in response to an antigen and can recognize and bind to it. Epitopes or antigenic determinants = specific molecular sites that antibodies bind to on antigens Humans can make as many as 100 million different antibodies! Fig. 16.3 Antibodies belong to the immunoglobulin superfamily of molecules. Table 16.1 shows the main types of immunoglobulins. These molecules function as the feelers that detect and bind to antigens. Don't memorize all the different types of immunoglobulins... Table 16.1 Fig. 16.3 Fig. 16.4. Basic antibodies Fig. 16.5. Model of an antibody. Figure 16.6. Protective outcomes of Antibody-Antigen binding 1. Neutralization 2. Opsonization 3. Prevent Adherence 4. Activate complement 5. Agglutination 6. Activate killer cells 2. Emerging Diseases New, reemerging, or drug-resistant infections whose incidence in humans has increased within the past two decades or whose incidence threatens to increase in the near future. Fig. 20.10. Some emerging infectious diseases. Most are old diseases that are re-emerging.
Some reasons for emerging diseases: increased international travel changes in food handling human encroachment on wilderness Cholera Caused by Vibrio cholerae Exotoxin Severe diarrhea climate change over use of antibiotics GAMMAPROTEOBACTERIA largest group of Proteobacteria many familiar genera - Escherichia, Salmonella, Pseudomonas GAMMAPROTEOBACTERIA (cont.) Vibrios some are important pathogens, e.g. Vibrio cholerae some Vibrio (and Photobacterium) species are capable of bioluminescence Some live symbiotically with squid or fish. incredibly diverse Figure 24.12 Scanning electron micrograph of Vibrio choerae Cholera (cont.) Emerging / evolution of a new strain with a capsule. antigen see Fig. 11.15 Figure 24.13 Mode of action of cholera toxin Table 24.5 Features of Cholera Viral Encephalitis (pgs. 675-677) - Epidemics usually caused by arboviruses (arthropod-borne viruses). Mosquitos are vectors and often reservoirs (main reservoirs are wild birds and mammals) (see Figure 26.13) e.g. West Nile Virus (an emerging disease) - Middle East to New York in 1999 and has now spread all the way to California (fall, 2003). 2947 cases and 63 deaths in Colorado in 2003 (reported to CDC), most of any state! Table 14.1. West Nile Virus is in the Flavivirus family (Flaviviridae) - ssrna. Many mosquito-vectored viruses in this group including Dengue and Yellow Fever viruses.
West Nile Virus cases reported to CDC in 2003 Note that the number of cases dropped off in Colorado in 1004 compared to 2003. This is because the birds (reservoirs) either died from the disease or became immune - thus the reservoir of the disease greatly decreased -this is why the disease spreads in a wave-like fashion across the world.. Slide from CDC, April 2004. Horses and humans are incidental (or terminal ) hosts, not reservoirs. Yellow fever Caused by arboviruses Zoonotic Affects the heart and blood vessels Vaccine available Figure 28.10. Distribution of Yellow fever - currently possibly spreading north into Central America and the SE USA Yellow Fever - another emerging disease that is spread by mosquitoes. Not a present problem in the USA, but the specific type of mosquito that spreads it has recently re-appeared in the SE USA. Important historically - prevented (along with Malaria) the French attempt to build the Panama Canal. Only after Walter Reed and colleagues showed that Yellow Fever was spread by mosquitoes were mosquito control measures put in place and work on the canal could proceed (read perspective 28.2, pg. 731). Features of Yellow Fever Table 28.7 Ebola An example of an emerging Hemorrhagic Fever caused by a Filovirus (Filoviridae), many such diseases exist in wild vertebrate populations and are potentially transferable to humans (e.g. Marburg outbreak among Germans who handled monkey meat). > Ebola first struck humans in 1976 in northern Zaire.
> 318 were infected, 88% died, including many hospital workers.!struck southern Zaire in 1995, but was quickly contained > Spread via air or contaminated blood > Incubation period 7-10 days. > 2-3 days later - nausea, vomiting blood, hemorrhaging 1989 - outbreak in Reston, Virginia. > rash, then death 6-9 days later 4 people acquired Ebola from infected monkeys Ebola is a filovirus because under the EM, it looks like a worm. Fig. 14.1c. Ebola virus. Table 14.1. Ebola and Marburg are Filoviridae. The Common Cold (pg. 573-574) most* caused by rhinoviruses, part of picornavirus family pico = small, rna = RNA non-enveloped like slightly cooler optimum temperatures (33 ) - adapted to the nose Reservoir is humans only as far as we know.. *About 15% of colds are caused by Coronaviruses (SARS is also caused by a Coronavirus).. Fig. 23.8 Table 14.1. Colds are caused mostly by Picornavirues and Coronaviruses.