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Understanding Viruses Reminder: EOC Monday Virus chapter – Chapter 24 What is the H1N1 virus? The current swine flu outbreak is caused by a new swine flu virus that has spread from person to person -- and it's happening among people who haven't had any contact with pigs. Here is a picture of the new swine flu virus, colorized and magnified Virus Nucleic acid – DNA or RNA Protein coat (capsid) Envelope in some – bilipid membrane from host cell that aids in virus recognize cells to infect What’s in a name? Letters represent 2 proteins on surface of virus: H – hemagglutinin N – neuraminidase Numbers refer to slight variations in The form of each protein the variations are significant b/c Our immune system has to recognize them Symptoms: Fever Cough Sore throat Body aches Headache Chills Fatigue Need lab test to determine if it is really H1N1 Prevention: Direct contact Touching an object they recently touched Flu germs start spreading up to a day before symptoms start, and for up to seven days after getting sick Treatment Sensitive to antiviral drugs Tamiflu and Relenza Most effective when taken within 48 hours Of the start of flue symptoms Most people do not need drugs A new vaccine will take 4-6 months to mak Viruses Viruses are not living organisms They are particles of nucleic acid, proteins, and lipids that reproduces only by infecting other organisms Viruses The typical virus is composed of a core of either DNA or RNA surrounded by a protein coat Influenza Virus Viruses are very specific in the cells they infect Plant viruses do not infect human cells; most animal viruses only infect certain animals. Infections Two ways: 1) Lytic infection: a virus enters a cell, makes copies of itself, and causes the cell to burst, thus spreading the virus 2) Lysogenic infection: a virus embeds it’s DNA into the host’s DNA and replicates along with the host cell’s DNA Avian Bird Flu Then why are people worrying about the Avian bird flu if only birds get it? Herpes HIV 1. 2. 3. 4. To make your plates follow these directions. Put one name on plate, date, hour Section off your petri dish into 4 sections, # the inside corners. #1 is your control Pick 3 things to sample to determine if bacteria is present. Sample area with tape. Headlines China confirms third person dead from H5N1 bird flu strain China confirmed its third human death from bird flu yesterday, saying a 41-year-old woman from the country's southeast succumbed to the virulent H5N1 strain. (Dec 30, 2005) HHS chief urges states to prepare for bird flu Health and Human Services Secretary Michael O. Leavitt urged each state yesterday to prepare for the possibility of a deadly avian flu pandemic by holding planning summits within four months. (Dec 6, 2005) Bird flu spreads in China, Indonesia BEIJING // China announced yesterday the spread of bird flu to a far western region, while Indonesia reported its first outbreak in the tsunamiravaged Aceh province, where hundreds of chickens have died of the disease. (Nov 25, 2005) What is H5N1? H5N1 Flu is a highly pathogenic strain of avian influenza (bird flu), first recorded in Hong Kong in 1997. Normally: non lethal, carried worldwide by wild bird populations in their intestines. Problem: this variant has mutated(changed) into the most fatal strain of avian influenza. Normally: this virus would not be harmful to humans. Problem: close proximity of humans to live chickens, pigs, and other animals, like on farms or marketplaces could cause the H5N1 virus to exchange genetic material with other viruses that more easily attack humans… it changes Problem: the H5N1 strain may jump the species barrier and cause severe disease, with high mortality, in people. It is feared that the H5N1 subtype could trigger the next pandemic. The H5N1 virus could either: •adapt, giving it greater affinity for humans, or; •exchange genes with a human flu virus, thereby producing a completely new virus strain capable of spreading easily between people, and causing a pandemic. Fighting Fire with Fire Fighting the deadly H5N1 flu virus may be done by using reverse genetics, where the virus's genes are rearranged in a lab to make a new strain. At the Core: Influenza viruses are constantly evolving (or _________) with eight genetic segments at their core that carry the instructions for replication. On their surface, they have two different types of protein spikes. 1. the hemagglutinin (HA), makes a virus stick to a cell to cause infection. 2. neuraminidase (NA), allows newly formed viruses to leave the host's cells. How vaccines work: When vaccinated, the human immune system makes antibodies that recognize these surface protein spikes. Then, when a virus with the same types of spikes tries to cause infection, the antibodies attach to the invader's spikes and fight it off. Great Idea!:To develop the H5N1 "seed strain" for making the first pandemic vaccine, scientists take the surface protein spikes of the bird flu virus (H5 and N1) and put them together with the genetic material of a harmless, master strain that's been used for decades to produce flu vaccines. How the virus spreads… through saliva, nasal secretions, and feces, other birds may pick up the virus through direct contact with these excretions or when they have contact with surfaces contaminated with this material The H5N1 virus is likely to spread throughout the world since migratory birds are some of the carriers of the virus. Past outbreaks of avian flu have often originated in crowded conditions in southeast and east Asia, where humans, pigs, and poultry live in close quarters. The virus is more likely to mutate into one that infects human under such conditions Q. What does it mean when scientists say the bird flu will evolve? Answer: It will CHANGE OVER TIME! Why are bacteria once controlled by penicillin becoming resistant to every antibiotic known? 1. They just don’t make antibiotics like they used to. 2. Doctors aren’t diagnosing illnesses properly. (They don’t make doctors like they used to.) 3. Pharmacies are dispensing cheap drugs. (They don’t make pharmacists …) 4. Medicine and agriculture make antibiotics part of the environment, so pathogens evolve drug resistance through natural selection. Why are bacteria once controlled by penicillin becoming resistant to every antibiotic known? 1. They just don’t make antibiotics like they used to. 2. Doctors aren’t diagnosing illnesses properly. (They don’t make doctors like they used to.) 3. Pharmacies are dispensing cheap drugs. (They don’t make pharmacists …) 4. Medicine and agriculture make antibiotics part of the environment, so pathogens evolve drug resistance through natural selection. So it isn’t surprising that mass media miss the boat ALMOST ENTIRELY Pathogens, parasites and hosts participate in two classes of interactions. 1. Evolutionary change in two contexts: a. change over time in the classic sense b. co-evolutionary relationships with hosts and their immune systems 2. Ecological interactions in two contexts: a. within the host’s body (“host as environment”) b. among multiple hosts and environments EVOLUTIONARY THEORY helps us understand new and emerging diseases because: 1. MICROEVOLUTIONARY CHANGES EXPLAIN: evolution of drug resistance, successes and failures of vaccines, and evolution of host resistance. 2. “MEDIUM” EVOLUTIONARY CHANGES EXPLAIN: how pathogens jump from one host to another. AIDS, SARS, influenza, and malaria) (Ex: 3. MACROEVOLUTIONARY CHANGES EXPLAIN: how particular pathogens come to affect certain hosts over long periods of time. An evolutionary perspective also makes it clear that ecological principles are essential to understanding what’s happening with infectious diseases. Why? Because … ECOLOGY DRIVES NATURAL SELECTION. (host as environment, medication, population growth, other ecological variables) HUMAN POPULATIONS GROW & MIGRATE. Changes in “human ecology” - the way we live, the ways we produce our food, etc., - alter host/parasite interactions. GLOBAL CLIMATE IS CHANGING. Climate affects ecological relationships between humans, other animals & plants, and pathogens. Why are so many new and emerging diseases these days? In large part because modern civilization is changing the ways that human populations, domestic animal populations, and wild animal populations interact. Why are so many new and emerging diseases these days? In large part because modern civilization is changing the ways that human populations, domestic animal populations, and wild animal populations interact. The evolution of drug resistance shows the relationship between evolution & public health. Alexander Flemming warned that overuse of penicillin would drive evolution of resistant bacteria. Antibiotic resistant bacteria now pose serious threats to public health. But did anyone listen to him? Or to evolutionary biologists who amplified his warning? In the same way, and for the same reasons, viruses can also evolve drug resistance. That’s why Darwinian theory is crucial to understanding challenges to development of either cures for, or vaccines against, HIV. Clip: Mutation and HIV from PBS Evolution Project Show 1: Darwin’s dangerous idea Evolutionary thinking is also useful in tracing the history of H.I.V. Where did this deadly virus come from? You’ve probably heard “Africa” -- but how? After HIV was identified, researchers discovered that many primate species in Africa are infected by similar viruses. Applying the same kind of genetic analyses used to construct evolutionary trees on a large scale, researchers examined the genes of these retroviruses to build their family tree. The results were fascinating The “bushmeat hypothesis” is interesting … But is it supported by any data? For years, transmission of retroviruses from apes to humans was known only in laboratory and zoo environments. But then … We now introduce an important term: ZOONOSIS. Definition: “A zoonosis is any disease and/or infection which is naturally transmissible from animals to man." Can you think of any zoonotic diseases in the news in recent years? (Mad Cow, Influenza, West Nile Virus, Lyme Disease, SARS, Ebola) Take influenza, as a “hot” example. Until recently, most of us thought of “the flu” as a strictly human disease. NOT ANY MORE! As the disease established itself and spread across Asia, the CDC and WHO stepped up efforts to understand how it was transmitted - among birds and from birds to people. Then, just as researchers began to think that domestic poultry were the main problem, H5N1 began to spread among several species of wild birds. And because some of those species are migratory, the virus has rapidly gone global, following the seasonal travels of the birds that carry it. Of course, birds aren’t the only thing that flies around the world these days, and therefore aren’t the only means by which the virus can spread around the world. Meanwhile birds aren’t the only animals affected by this epidemic. Because as various bird flu strains are spreading and reproducing in millions of wild and domestic birds, they are also mutating … in potentially dangerous ways. So ... what DO we know for certain? That the bird flu epidemic is dangerous because the influenza virus is evolving! (Which is good news for viruses, but could mean trouble for us.) Why are some flu strains just a nuisance, while others are dangerous? Because of the way our immune system identifies and attacks pathogens. What happened? Can it happen again? The answers relate to the nature of influenza as an evolving zoonosis -- and a phenomenon we could call “viral sex.” Why is this zoonosis so important? Because although all influenza strains belong to the same viral “species,” some populations are reproductively isolated from each other in different hosts. This isolation means that not all strains have the same kind of genetic variation. And that variation can spell trouble for the human immune system. There are actually three parallel routes, any or all of which could transform the current situation into a deadly pandemic. What’s the quick summary of what we know so far? The 1918 flu virus appears to have jumped, directly, from birds to humans. That jump, high virulence, and human-human transmissibility appear to be dependent on a small number of changes in the flu genome. Certain evolving strains of the current H5N1 avian flu strains have accumulated 5 of an estimated 10 mutations related to human-human infectivity. What’s are some highlights of stuff we DON’T know (yet)? What is the likelihood that H5N1 evolution will produce a form that efficiently infects humans? What is the likelihood that H5N1 evolution will produce a form that transmits efficiently from human-human? Can we produce a “universal” flu vaccine?