Cells 4- Infectious agents Flashcards
(27 cards)
How might Ebola reoccur in the future
Potential for wildlife spillover- concentrated human population in west Africa- animal reservoirs- humans will come into contact with low grade animals
Methods through which the ebola virus crossed species barrier.
Schematic of virus spillover from wildlife and human-to-human transmission.
Pathogen spillover to humans is typically associated with the use of bushmeat and direct contact with tissues and/or bodily fluids through handling and eating of infected animals (A), e.g., duiker, primates, or fruit bats [13]. Predation and consumption of a red colobus monkey by chimpanzees has also been linked to an outbreak of Ebola among chimpanzees and one researcher in Côte d’Ivoire [14]. Ingestion of fruit contaminated with Ebola-infected bat saliva or feces may be another mechanism by which bats might infect other involved wildlife species (e.g., duiker, nonhuman primates) or even humans. Human-to-human transmission has been associated with traditional burial practices, caregiving, or some other form of direct physical contact with infected individuals or bodily fluids [15]. Transmission dynamics in high-density urban centers (C) will differ importantly from rural villages (B), influencing outbreak progression and control efforts. Transmission in the hospital setting is largely associated with failures in infection control procedures and standard barrier precautions (D), many of which are related to inadequate staffing, infrastructure, and financing of health care systems [16,17].
Why did Ebola not kill the Bats
Ebola virus entry requires the cholesterol transporter Niemann–Pick C1
An Npc1 mutation in these bats leads to low grade infection and carrier status. However, it is not known whether the bats already had this mutation, or if they developed it as a form of resistance.
Why are we interested in infectious agents
Cause over 50 million deaths globally each year.
Infections- people unable to work-economies crash.
Need to be ready to develop future vaccinations for mutates strains of pathogens which could otherwise cause a pandemic.
Stop anti-biotic resistance- create more powerful treatments that work quicker
Develop better vaccines for high burden countries.
Stop bioterrorism
How does the bacteria causing meningitis become pathogenic.
It is originally commensal in the larynx- but then enters the bloodstream where it becomes pathogenic and leads to a community infection.
What are two common types of hospital infection.
Methicillin Resistant
Staphylococcus aureus
Clostridium difficile
Compare the mutation rates of humans, bacteria and viruses.
Viruses have a high point mutation rate- as they have no proof-reading mechanism- this combined with a short generation time means that mutations spread rapidly throughout the population- making them very pathogenic.
Bacteria and humans have similar rates of point mutations- however bacteria have shorter generation times- meaning mutations spread more rapidly.
What is capsule switching in bacteria
A change in the polysaccharide capsule surrounding bacteria due to gene transfer- worry that vaccine of subgroups of meningitis would do this- creating a new, untreatable strain.
What are the 5 types of infectious agent
Bacteria Virus Protozoa Fungus Helminth parasites
What are the differences between eukaryotes and prokaryotes
1) Prokaryotes do not have internal membranes
(few exceptions of photosynthetic bacteria)
Eukaryotes do have internal membranes that define organelles including nucleus, ER, mitochondria, etc
2) Prokaryotes have a single copy of a chromosome (haploid)- only one copy- hence mutation is immediately expressed.Eukaryotes can be haploid or diploid
3) Eukaryotes have cytoskeleton
Prokaryotes cytoskeleton is not as well defined.
4) Cell wall of prokaryotes contain peptido-glycan- gives shape to bacteria.
What are the key properties of viruses
not cells in their own right- OBLIGATE PARASITES- only replicate in a host cell.
Contain RNA or DNA genetic material
Make use of a host cell nuclear synthetic machinery to replicate
Show host specificity but infect almost all other life forms, including bacteria
Divide by budding out of host cell- when enough viruses are made- pinch out of cell.
Various routes of infection
An example of an infection caused by viruses
HIV- retrovirus- reverse transcriptase- converts RNA to DNA to make protein
What are the distinguishing features of bacteria
Fundamentally different from all other living things in being PROKARYOTES (cell wall composition)
Contain a chromosome of DNA but no nucleus, but in condensations called Nucleoids
Widely distributed in nature
Some are pathogenic
eg. Neisseria and Shigella- gastrointestinal infection.
Divide by binary fission- organelles replicate..
Various routes of infection
Flagella give bacteria motility- particularly for bacteria living in water.
An example of an infection caused by bacteria
Shigella- invades epithelium of intestine- often caused by lack of sanitation
How does shigella invade the epithelium
Cell entry-vacuole lysis- intracellular replication- cell to cell spread using the actin of the host.
What are the characteristics of septicaemic disease
rapid progression
septic shock
severe inflammatory response
What are the characteristics of fungi
Eukaryotic
occur as yeasts, filaments or both
yeasts bud or divide; filaments (hyphae) which have cross walls or septa
cause cutaneous, mucosal and/or systemic mycoses
An example of an infection caused by yeast
Candida albicans
How does candida albicans reproduce
Switches between budding and filaments depending on nutrients in the environment- different life cycles.
What are the characteristics of Protozoa
Unicellular eukaryotic organisms
include intestinal, blood and tissue parasites
replicate in the host by binary fission or by formation of trophozoites inside a cell- infect cells- make daughter cells inside that
many have a complicated life cycle involving two hosts- hard to know which stage to treat.
infection is acquired by ingestion or through a vector
eg insect or invertebrate vector
Examples of infections caused by protozoa
Malaria
Leishmania spp-Leishmaniasis
What is Cutaneous leishmaniasis
Cutaneous leishmaniasis affects the skin and mucous membranes. Skin sores usually start at the site of the sandfly bite. In a few people, sores may develop on mucous membranes.
Describe the characteristics of Helminth parasites
Roundworms
Flatworms (flukes)
Tapeworms
Metazoa with eukaryotic cell structure Multi-cellular Visible to the naked eye Have life cycles outside the human host Life cycle complexity varies from simple embryonation to alternation of generations in different hosts- different larvae stages.
Examples of infections caused by helminth parasites
Roundworm- faecal-oral transmission
Flukes/Flatworm- Eggs travel through hepatic portal vein from liver to gut- spindles- damages tissues.
