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| Epidemic | A disease that dramatically increases its incidence and prevalence in a short period of time. Can be infectious or non-infectious. Examples: Flu (infectious) and obesity (non-infectious) |
| Pandemic | An epidemic that occurs on a global scale. HIV is a pandemic, because its incidence and prevalence have increased dramatically in populations worldwide |
| Endemic | A disease that has a long history in the population, with little change in prevalence or incidence over time. Malaria is known as the "original" endemic disease due to its history in various regions of the world and thus its adaptive (selective) impact on human populations |
| Disease | Condition impairing normal function. It’s a biological definition relying on measures of physiological state. Doesn’t require recognition by the individual (they can be sick without knowing it). |
| Illness | Sufferers interpretation of disease. Understood and treated in a particular social and cultural context. It’s the subjective experience of disease, acknowledged by the sufferer. |
| Infectious disease | A disease resulting from the presence of pathogenic microbial agents. They can be passed from host to host. All infectious diseases require at least two factors, host and agent. 4 classes of infectious pathogens are: viruses, bacterium, fungus, and helminth |
| Chronic diseases | In medicine: long-lasting or recurrent disease. They can’t be transferred from person to person (non-communicable). Breast cancer is an example. |
| Innate immunity | It is genetically inherited, non-specific, and occurs immediately (first & fastest). Response is similar whether you cut yourself or come into contact with a virus. Components are: Barriers (skin and chemicals made by body, like mucous); Inflammation; Fever; Phagocytosis (cells eat other cells) |
| Acquired (adaptive) immunity | Is conferred after contact with a causal agent. It’s time-delayed (takes longer than innate). Triggered by antigens (proteins found on bacteria, pollen etc), and identifies them as foreign → this response is specific to the antigen. Two types of response: Humoral: B-cells create proteins called antibodies (immunoglobulins) which bind to specific antigens; Cellular: ‘killer’ T-cells kill, ‘helper’ T-cells activate phagocytes or B-cells. Two notable properties are specificity and memory |
| Vaccination | Presents a pathogen’s antigens to the immune system, stimulating immune response, creating antibodies and a memory of the infection without the danger of an actual infection. Memory helps protect from the disease if person is re-exposed to the pathogen later. Vaccine has inactive, non-replicating bacterium in it. |
| Adaptations to disease | A range of mechanisms, responses and traits that enhance survival in face of environmental pressures, such as disease. Can be Physiological, genetic, developmental or cultural. Example: Sickle cell heterozygosity in response to Malaria |
| Zoonoses | Any diseaseor infection that is naturally transmissible from vertebrate animals to humans. Can be any class of pathogens, can be transmitted directly or through vectors. An example of this is the Hantavirus, which finds its reservoir in deer mice. More than half of all infectious diseases are zoonotic. Becomes increasingly problematic as human pops encroach upon wildlife habitats etc. |
| Host | An individual either infected with or potentially infected with a parasite. |
| Causal agents | The organisms that cause disease. Include bacteria, viruses, fungi, protozoa (biological agents) |
| Vectors | Organisms (usually arthropods) which transmit the causal agent from one infected host to a new host. Vector-bore diseases tend to be most virulent (don’t rely on host mobility for spread, rapid multiplication is higher likelihood of transmission in blood, incapacitation may increase contact w vector). Example: Mosquitos serve as vectors in the spread of Malaria, as it carries the parasite from host to host when it takes blood meals from them |
| Virulence | Harm done to a host by a pathogen (tendency to reduce survival or reproductive capacity of host). Diseases that rely on person-to-person contact tend to be less virulent, because host must be healthy enough to contact/infect others. Vector-borne diseases (ie. malaria) tend to be more virulent. Evolution doesn’t inevitably lead to more benign pathogens (depends on likelihood of transmission). Ex. Malaria |
| Pathogens | Microorganisms that cause disease in a host. Examples include the Flu virus, the HIV retrovirus, and infectious prions that cause Kuru |
| Edge effect | Fragmenting forests into small patches separated by agricultural activities and human habitation increases the “edge effect”: Promotes interaction between pathogens, vectors, and hosts; Fewer predators of small mammals; Reduced biodiversity reduces number of alternate (non-human) hosts. Example: Lyme disease |
| Antigenic drift | A pathogenic strategy that occurs when mutations in the genes of a virus allows it to spread through populations that are partially immune because the mutated virus can’t be stopped as quickly by the antibodies that were formed to target previous strains. Occurs with influenza A and B viruses |
| Modes of transmission: Airborne | Agents present in nasopharynx or respiratory tract and disseminated in salivary droplets during coughing, sneezing, breathing |
| Globalization | The process of increasing trade, travel and contact on a global level. Due to increased globalization, localized problems can quickly become global problems (with infectious diseases). Example: SARS, which spread globally with the help of airplane travel |
| “Sit and wait” pathogens | Pathogens that are durable in the environment outside of the host. They tend to be among the most virulent pathogens. |
| Paleolithic baseline | Hunter-gatherer society for 99% of human history (small, isolated groups). Low population density + high mobility prevented many diseases from becoming endemic. These groups made it hard for infectious disease to decimate a large number of people, as it would just kill off isolated groups. Paleolithic diseases were probably: Parasites; common bacteria; viruses with long latency; zoonoses (including ebola-like viruses) |
| Emerging infectious disease | New, previously unknown infectious agent/disease OR previously described infectious agent presenting: in a new location; as a new syndrome; in a new host; with increasing drug resistance pattern or new genetic characteristic that changes range or pathogenicity. Usually zoonotic or vector-borne. Changes to land/climate can drive emergence of new infections/changes in transmission. Example: Malaria's ascent in east African highlands (Zimbabwe) can be blamed on recent climate change |
| Prevalence | The total number of individuals with the disease in a particular time period |
| Incidence | The number of new cases in a particular time period |
| Morbidity | Refers to disease; rates of morbidity describe the prevalence of a disease in a population |
| Mortality | Refers to death; mortality rates are the prevalence of death, usually attributed to a given disease, in a population. |
| Herd immunity | Occurs when the proportion of people in population that are immune to an infection is sufficiently high so that transmission to vulnerable members of population is greatly reduced. This prevents outbreaks of the disease and protects those who are (immunocompromized, newborns, etc). |
| “Structural violence” | Discussed by Farmer.Describes social structures (economic, political, legal, religious, and cultural) that stop individuals/groups from reaching their full potential. Sources include poverty, gender, education, racism and homophobia. |
| Social determinants | The circumstances in which people are born, grow up, live, work, and age, as well as the systems put in place to deal with illness. Circumstances are shaped by forces like economics, social policies, and politics. |
| Modes of transmission: Water and food-borne | Agents passed in feces may find their way into the water/food supplies (the fecal-oral route) |
| Modes of transmission: Vector borne | Transmission is by an organism (vector), usually some insect. This is how malaria/river blindness are spread |
| Modes of transmission: Physical contact | Like HPV (STI). Can also be things like prions, which have indirect physical contact (hard to kill).There can be prion based disease spread in hospitals if scalpels aren’t cleaned well enough. |
| Example of Herd Immunity: | Measles: a highly infectious respiratory disease caused by a virus, very contagious, therefore requires high levels of vaccination to ensure herd immunity (85% to prevent outbreaks). Anti-vaccination campaigns have caused a reduction in measles vaccinations, which has resulted in higher cases of measles in the UK |
| Example of Structural Violence | Racism: is a form of structural violence. It has been shown to hinder black’s access to timely therapeutics for HIV in comparison to white’s, regardless of disease stage (1990s Baltimore study). |
| Malaria | A disease caused by a protozoan and transmitted by mosquitos. Characterized by regular high fevers/parasitization of red blood cells. There are several known genetic adaptations of the disease, suggesting its importance in the evolution of many human populations. Disproportionately impacts poor, tropical populations |
| Polio | Caused by Polio virus, highly contagious, spread by p-t-p contact, contact with infected mucus, contact with infected feces. Most who contract don’t show any symptoms, and only in 1% of cases is there paralysis |
| What makes Polio so hard to eradicate? | Spreads quickly, virus can spread through oral fecal route or through person-person contact; cultural resistance and rumor spreading made vaccination harder; there are asymptomatic carriers; civil unrest made vaccination much harder |
| Smallpox | Caused by a virus, only effective treatment is a vaccine. Humans are the only natural host; transmission from prolonged person-to-person contact. Eradicated by public health campaign that focused on a “circle strategy” that targeted villages where infected individuals were present (Nigeria) and door-to-door strategies (India). |
| What made smallpox easier to eradicate? | Visible infection; no animal vector; low mutation rate; no asymptomatic carriers; short incubation; easily administered vaccine; use of local networks (ie. missionaries, young boys) and cultural aspects (shrines in India) |
| HIV | Human immunodeficiency virus, an RNA retrovirus that infects T-cells. It’s the leading cause of death for adults ages 15-19, and it disproportionately impacts Sub Saharan Africa. It’s especially dangerous because of its high rate of mutations, which can allow it to become resistant to some treatments |
| Tuberculosis | A highly infectious bacterial disease caused by Mycobacterium tuberculosis. It infects macrophages in the lungs, and ultimately results in the liquification of lung tissue. It's a great example of how a disease can become drug resistant, as it requires a very long antibiotic regimen |
| Schistosomaisis | A helminth infection caused by a parasite that causes damage/bloating in internal organs. Mostly impacts women and children. In poorer countries that lack good water sanitation there has been increased prevalence. In China and East Asia, rice farms and dams led to growth of snails, which host the parasite, and therefore increased the diseases prevalence. |
| Lyme disease | Tick carries disease, which has an incubation period of several days to several years. If left untreated it can cause severe debilitation. Transmission has increased because of urbanization (edge effect) and it’s the most common vector borne disease in US |
| Kuru | A prion disease found among the Fore of New Guinea. It was transmitted through consumption of infected individuals after they died. Was originally thought to be genetic, but research by anthropologists revealed that complex family networks weren’t always based on biological relatedness. |
| Chagas disease | Caused by protozoa, transmitted by reduvid bug. Chronic 10-20 years after infection. It's an example of a re-emerging disease that's directly related to poverty, as the bugs live in the mud walls of huts in impoverished areas. |
| Hantavirus | Is caused by a RNA virus that found in deer mice. Infected rodents shed virus in their urine and droppings, and people become ill when breathing in dried aerosolized mouse excreta. There’s no human-human transmission. Increased human contact with hanta virus can occur as a result of people moving into new areas, and environmental conditions (like increased rain) that encourage growth of the mice’s main food sources. |
