7.1.1 - Causes of Infectious Disease Flashcards
(21 cards)
Disease
Anything that adversely affects the normal functioning of a living thing or parts of a living thing.
An infectious disease is caused by another oganism, or an infective agent known as a pathogen.
Pathogen
single celled: microbes such as bacteria, protozoa, yeasts
multicellular: fungi, worms
non-cellular: viruses and prions
Pathogen - Bacteria
- Single celled prokaryoteic organisms. They have a cell wall but no membrane-bound nucleus or organelles.
- Bacteria reproduce by an asexual process known as binary fission. Generation time is between 10 minutes and 24 hours.
- Bacteria are larger than viruses but smaller than protozoans.
- Genetic material in two forms: bacterial DNA in the form of a large circular chromosome or smaller circular DNA fragments called plasmids.
- Can be aerobes, anaerobes or facultative anaerobes
Transmission:
* Directly through close contact with another infected host organism, or indirectly through contact with an object contaminate with the bacterium.
* They are used by humans to create vaccines and antibiotices. They can inhabit multicellular organisms in a beneficial, symbiotic relationship - 1000 trillion bacteria in the human body.
Examples:
* Tuberculosis by myobacterium tuberculosis – fever, cough
* Salmonellosis (food poisoning) by salmonelle enterica – vomiting and diarrhoea
Meningococcal meningitis
Mandatory vaccine for NSW high school students.
Meningococcal disease is a serious bacterial disease that can cause acute illness and death due to bacterial meningitis (bactieria in the brain) and septicaemia (bacteria in the blood)
Symtoms: fever, headache, stiffness of the neck and pain in the joints, photophobia, red-purple rash
Pathogen - fungi
- Eukaryotic organisms that have a cell wall composed of chitin. Heterotropic - do not contain chlorophyll
- Microscopic and macroscopic
- Reproduce asexually, while others reproduce using sexual and asexual reproduction.
Transmission of fungal disease:
* Fungal infections may be cutaneous, subcutaneous or systemic depending on the severity of infection
Examples:
* Rose garderner’s disease sporothrix schenckii (foundin soil and plants) – severe skin infections
Tinea
Athlete’s foot
- The warm and moist environment of a public shower provides ideal conditions for the growth and spread of fungal pathogens.
- Common fungal disease.
Symptoms: redness, itching around the toes, scaling of the skin, nail deformities
Treatment: antifungal creams for an extended period, as after symptoms are gone, spores need to be treated.
Pathogen - Protozoa
- A single celled eurkaryotic organism with membrane bound nucleus and organelle, and no cell wall.
- Reproduce by binary fission
Transmission: by insect bites, which transfer the disease between hosts or through faeco-oral route.
Examples:
* Malaria
* Sleeping sickness
* Amoebic dysentry - transmitted in contaminated water
Giardiasis
Giardia lamblia are protozoal organisms that live in the human gastrointestinal tract and are possible sewage and pool contaminants.
Transmission: As it is resistance to chlorineunder normal pool operating conditions, swallowed infected pool water is the main source of transmission.
Symptoms: Infections cause abdominal cramps, chronic diarrhoea, bloating and weight loss.
Often infants, children
Macroparasites
Visibe to the naked eye. Some cause disease directly or act as vectors in the transmission.
Endoparasites: live in the host body - flatworms, roundworms
Ectoparasites: live outside, often sucking blood - mosquitoes, fleas
Helminths
Worm like organisms present in the gastrointestinal system (endoparasites). They disrupt normal digestion and absorption of gut conents.
Transmission: Comlex life cycle.
* All reproduce using eggs.
* Larvated eggs are ingested and mature into adult worms that feed on the hosts nutritents (digestive system). They lay eggs in the large intestine.
* Eggs are passed in faeces into the environment.
* Next host picks up the eggs through unsanitary water or infected soil.
Examples:
* Roundworm (toxocara casis in dogs), tapeworm (taenia soilum in pigs) that causes a lack of appetite, weight loss, blood in faeces, worms may be visible in faeces.
Heartworms
A parasitic helminth.
Heartworms are long, thing worms that live in the right side of the heart as adults and block the flow of blood. They cause damage to the lining of the heart, the valves and the pulmonary veins that exist the right side of the heart.
Symptoms: cough, accumulation of fluid in the abdomen and lungs. Liver often swollen, affected dogs would suddenly collapse.
Transmission: mosquitos, as they bite infected hosts and transfer it to other dogs. Cats can also be infested.
Treatment is often as dangerous as the disease, as a mass of dying worms can dislodge from the heart and block major blood vessels.
* Currently, immiticide is the only drug available for heartworm therapy.
* Therefore, prevention is important - with several medications available and recommended for all cats.
Parasitic arthropods
Ectoparasites which cause disease in humans, animals and plants.
Fleas: live in animals hosts, often cats and dogs, to feed on blood.
* Manifests as hair loss and skin redness.
* Eggs are laid in the environment, hatching at vibration and increase of CO2 levels - presence of hosts.
Ticks: ectoparasites that take blood from the host.
* Inject neurotoxin that can lead to progressive paralysis - first sign in dogs in dysphonia (strange barking), dysphagia (difficulty in swallowing), ataxia (staggering gait) and potentially life threatening paralysis.
Lice: have sucking and biting mouth parts. Can cause anaemia in infested animals (sucking blood).
* E.g. head lice are a common problem in primary schools and childcare due to contact between children.
Mites: don’t necessarily bite - depends on species, but still feed on blood, skin or other tissue of hosts (often animals)
* Symptoms: generally cause skin irritation, respiratory and skin problems due to human allergies.
* E.g. dust mites can trigger asthma attacks.
Flies: common housefly non-biting, but capable of transmitting pathogens between hosts.
E.g. fly strike in sheep is caused by the sheep blowfly. Eggs are laid in the skin of the sheep, larvae burrow into the skin and feed on the flesh, causing infections.
Stable fly: can lead to reduced weight gain in the horse due to continual agitation from fly biting.
Large populations of flies, with constant irritation can lead to severe stress to animals (shaking head, flapping ears) even developing heat stroke in summer.
Mosquitos: biological parasites as they benefit by having blood meals from their hosts. They act as vectors, transferring pathogens from one host to another.
* E.g. yellow fever, Dengue feve. Zika virus transmitted by monsquitos has dangerous effects on unborn foetus
Noncellular pathogens
Viruses (single - viron)
These are non-cellular and have both living and non-living characteristics (depending on environment):
* Genetic material in the form of nucleic acids and can pass on hereditary information
* Not free living – reproduction and metabolism only possible through a host
* Not composed of cells, can be crystallised.
Structure:
* Viewed only with an electron microscope
* Consist of a protective proetein that encloses the genetic material (infectious part of the virus)
* Single strand of RNA is not possible to perform all the functions of a living organism
* Some have a lipid membrane
Replication:
1. Viral protein coat contains chemicals that allows the virus to attach to host cell and inject nuclei acid (genetic material)
2. Cell makes copies of virus DNA (taking over machinery of the cell). Some viruses use the cell membrane to form their own lipids and glycoproteins.
3. Cell uses mRNA to make virus proteins
4. Cell bursts and releases new viruses.
Example:
* Influenza
* Measles
* AIDS, caused by human immunodeficiency virus (HIV)
Treatment: treatment of viral diseases is difficult as any attempt to kill the virus will also affect the host cells. Some antiviral medications are available; but treatment focuses on managing symptoms and supporting immune system.
Pathogen - prions
Pathogenic prion is an abnormal protein that is capable of causing degnerative disease of the nervous system.
Structure
* Prions do not contain any genetic material.
* Prions are the smallest of all pathogens.
* Normal prion proteins and pathogenic prion proteins have different shapes.
Disease is caused when pathogenic prions induces abnormal folding patterns in normal proteins they come in contact with.
Transmission:
* Ingesting
These diseases are known as transmissible spongiform encephalopathies (TSEs) - brain tissue is full of holes.
Symptoms:
* Long incubation period (5-20 years), but can progress rapidly once clinical signs appear.
Mutated genes can be passed on to
Examples:
* Scrapie in sheep and goats
Kuru
Symptoms: trembling, uncontrollable laughter, rapidly progressed to death
Due to the practice of eating the brain of the dead, to spare the indignity of being eaten away by worms.
Classifying pathogens - microscopic, non-cellular, proteins
Prions
Classifying pathogens - microscopic, non-cellular, protein coat
Viruses
Classifying pathogens - microscopic, cellular, prokaryote
Bacteria (no nucleus)
Classifying pathogens - microscopic, cellular, eukaryote
Fungi, protozoans
Classifying pathogens - macroscopic, live outside body
Ectoparasites
Classifying pathogens - macroscopic, live inside body
endoparasites
