Communicable Transmission

• What is necessary for pathogens to survive?

  They must transfer from host to host
• What happens if pathogens cannot find new hosts?

  They will go extinct
• How is disease transmission defined?

  Transfer of pathogens from infected to uninfected host
• Why do pathogens produce many individuals during infective stages?

  To increase likelihood of finding new hosts
• How can some pathogens be transmitted?

  Through physical contact between individuals
• What occurs when TMV-infected plant leaves touch uninfected leaves?

  Particles of the virus are transmitted
• How are influenza viruses spread?

  Via tiny droplets of water in the air
• What are spores in the context of pathogen transmission?

  Small reproductive structures released into the environment
• How do spores reach a food source?

  They are dispersed via wind or water
• What type of spores does P. infestans produce?

  Sporangia
• How is HIV transmitted?

  By direct exchange of body fluids
• What is a key characteristic of HIV?

  It is a retrovirus
• How does HIV survive outside the human body?

  It cannot survive outside the human body
• In what ways can HIV be transmitted?

  Sexual intercourse, blood donation, sharing needles
• How is tuberculosis (TB) transmitted?

  Through inhalation of droplets from infected individuals
• What bacteria causes tuberculosis?

  Mycobacterium tuberculosis
• Why does TB spread quickly in overcrowded conditions?

  Infected droplets are easily inhaled by others
• How does Mycobacterium bovis spread to humans?

  Through contaminated meat and unpasteurized milk
• What is a vector in disease transmission?

  An organism that transfers a pathogen between hosts
• What type of organisms are common disease vectors?

  Insects
• Why are insects ideal vectors for disease transmission?

  They reproduce in large numbers
• What causes malaria?

  Protoctist Plasmodium
• How is Plasmodium transmitted to humans?

  By female Anopheles mosquitoes
• What happens when a mosquito bites an infected person?

  The mosquito takes up Plasmodium with the blood meal
• How can malaria also be transmitted besides mosquito bites?

  During blood transfusions and unsterile needles
• What factors affect disease transmission?

  Presence of pathogens and susceptible individuals
• What is the effect of a high number of immune individuals in a population?

  It reduces the likelihood of transmission
• How do resistant individuals differ from immune individuals?

  Resistant individuals do not develop symptoms upon exposure
• What genetic trait provides resistance to malaria?

  Heterozygous for the sickle cell allele
• How does the proportion of resistant individuals influence transmission?

  The higher the proportion, the lower the probability of transmission
• What factors affect transmission of human pathogens?

  Human behavior and population size
• Where are high infection rates likely to occur?

  In areas with high population densities
• How does overcrowding affect TB transmission?

  It increases the likelihood of inhaling infected droplets
• What agricultural practice can lead to disease outbreaks?

  Monocultures
• How does the biology of vectors affect pathogen transmission?

  It influences the population of vectors
• What environmental conditions favor Anopheles mosquitoes?

  High rainfall, high temperatures, high humidity
• Why is malaria found predominantly in Africa?

  Because Anopheles mosquitoes prefer biting humans
• What was the outcome of the WHO's eradication program for malaria?

  It was mainly unsuccessful
• Why did Plasmodium become resistant during the eradication program?

  Due to the drugs used for control
• How did Anopheles mosquitoes become resistant during the eradication program?

  To DDT and other insecticides