Chapter 9 Global Infectious Diseases affect everyone Parasites Few developed countries think of infectious diseases as a major problem Many parts of the world they still are Everyone should be concerned about infectious diseases because they have potential to Parasites eukaryotic organisms that survive off a living host Some parasites only minimally affect their hosts but others can cause serious illness or Protozoa single celled organisms that have animal like characteristics and often live in disability water o Classified by how they move and characteristics of lifestyle Helminthes are endoparasitic worms that live inside the body of the host o Classified by shape and lifestyle o Acquired by walking barefoot in contaminated soil wading in contaminated water ingesting contaminated good or water and by being bit by worm infested insects Ectoparasitic animals that live on the exterior surface Antiparasitic medications will kill many parasites But some are becoming drug resistant Fungi Fungi come in many forms including molds and yeasts Fungal conditions frequently occur after bacteria that normally live in the body are Important decomposers disturbed by antibiotic use or immunosuppression Prions pertinacious infections particles Cause rare degenerative nervous system diseases called transmissible spongiform Live in moist dark places Prions encephalopathy TSEs No treatment so prevention is essential Exposure infection and disease Natural history describes usual timeline from exposure to particular agent to infection to either recovery or death Not all exposures cause infections Some people are more vulnerable and immune system is weakened by age malnutrition cancer treatments immunosuppressive drugs or existing infections with other pathogens Infectivity capacity of an infectious agent to cause infection in a susceptible human o Measured by calculating secondary attack rate average number of other people that one contagious person affects Infection occurs when infectious agent begins to reproduce inside a person Latent phase incubation period immediately after infections infectious agents multiplies in the host but the infected individual does not feel sick Detection in early stage can be critical Infectious Disease Transmission Disease occurs when infected person develops symptoms or illness not call infections cause disease Pathogenicity capacity of an infectious agent to cause disease in an infected human and measured by the proportion of individuals with laboratory confirmed infection who become ill Those who develop symptomatic disease there are three possible outcomes death recovery within immunity recovery without immunity Most infections the recovery rate is high Virulence ability of an infectious agent to cause disease or death in a host and is measured by the proportion of severe or fatal cases among all people who have the disease Virulent infections will have high case fatality Some infections are acute short term Others are chronic long term Chronic infections can increase susceptibility to other infections and some chronic infections increase risk of cancer Infections spark an immune process that forms memory antibodies in the blood that allow the body to quickly destroy nay new pathogens of the same type to invade the body in the future Many modes of transmission Direct transmission is person to person transmission when susceptible person touches an infectious person s blood or other bodily fluids then touches his or her moth eyes nose or other portal of entry Frequent hand washing and use of protective equipment can help prevent transmission Airborne transmission occurs when pathogens are aerosolized or suspended in the air and people breathe in that contaminated air May need to treat person in isolation Vector borne infections are spread by vector insects Can be partially attained through the use of insecticides Animals can play a role in the infection transmission process Fecal oral transmission occurs when person ingests products contaminated with fecal material from animals or humans Indirect transmission can occur as a result of contact with inanimate objects called fomites Vertical transmission mother to child transmission could be passed to fetus during pregnancy delivery to baby or through breast milk To control infectious diseases several other aspects must be considered Reservoir environment home for infectious agent Antroponoses infectious diseases that usually only happen in humans Zoonoses infectious diseases that usually occur in animals and only occasionally affect humans Cycle of infection how infectious agent cycles between different species Each host in the cycle of infection must be considered for inclusion in an infection control plan Diarrheal and foodborne diseases Infectious diseases illnesses cause by communicable pathogens are often classified based on primarily symptoms they cause the mode of transmission or by other key features Most diarrheal infections and other forms of infectious gastroenteritis are spread by fecal oral transmission Cholera infection causes severe watery diarrhea Typhoid paratyphoid shigellosis salmonellosis and campylobacteriosis are also Protozoan infections can also be spread through food and water that has been bacterial infectious diarrheal diseases contaminated by animal feces Viruses are even more common as a cause of diarrhea Most diarrheal infections are short term but some can be chronic Effective methods for prevention of diarrhea include safe food handling frequent hand washing consistent access to clean drinking water and community wide sanitation Respiratory diseases often caused by viruses Upper respiratory infections like cold and lower respiratory infections like pneumonia are Most respiratory infections are acquired through air Prevention methods for respiratory infections include isolating infected persons reducing exposure to smoke vaccinating members of vulnerable population groups and encouraging frequent hand washing and the covering of the nose and mouth when coughing or sneezing Several types of bacterial and rickettsial infections are spread by the bites of infected Vectorborne diseases ticks and fleas Viruses spread by anthropods such as insects and arachnids are called arboviruses Vectorborne protozoan infections are of particular global health concern African sleeping sickness is spread by the bite of infected tsetse flies and can cause chronic fevers and headaches that lead to paralysis