Communicable Diseases Flashcards
Communicable diseases?
Diseases that can be passed from one organism to another, of the same or different species
What are pathogens?
Infective microorganism which cause disease
Pathogens include?
Viruses, fungi, bacteria and protoctista - each with their own characteristics
Communicable diseasess?
Animals they are most commonly spread from one individual of a species to another (intra) but they can also be spread between species (inter)
In plants they are spread directly from plant to plant
Vectors carry pathogens from one organism to another - common vectors include water and insects
Bacteria
Small proportion of them are pathogenic and cause communicable diseases
They are PROKARYOTES so their cell structure is very different from eukaryotic organisms they infect - no membrane bound nucleus/organelles
How can bacteria be classified?
By their basic shape rod shaped (bacilli), spherical (cocci), comma shaped (vibrios), spiralled (spirilla) and corkscrew (spirochaetes)
By their cell walls - two main types react differently to the process of gram staining ; gram positive bacteria look purple-blue under the light microscope but gram negative bacteria appear red (counter stain of safronin is applied) - this can be used to identify how bacteria react to different antibiotics
Gram staining
Crystal violet and iodine is applied to fix the dye
Then is washed with alcohol (penetrates the cell walls and allows the violet-iodine complex to leak out) - gram positive bacteria retain the violet stain and appear blue/purple while gram negative bacteria have thinner cell walls so they lose the stain and they appear red (counterstain applied)
Gram positive bacteria are susceptible to penicillin which inhibits the formation of cell walls while gram negative bacteria have much thinner cell walls so are not susceptible to penicillin
Viruses?
Non-living infectious agents and 50 times smaller in length than the average bacterium - basic structure is just some genetic material surrounded by a protein
They invade living cells where the genetic material takes over the host cell to make more viruses - reproduce rapidly and evolve rapidly too
They are all pathogenic and cause disease in every other type of organism
What are bacteriophages!
Viruses that attack bacteria - use bacterial cells to replicate and destroy the bacteria at the same time ; used to identify and treat some diseases and they are very important in scientific research - PARASITES
Protoctista
A group of eukaryotic organisms with a wide variety of feeding methods - they include single-celled organisms and cells grouped into colonies. A small percentage of protoctista act as pathogens, causing devastating communicable diseases in plants and animals - these are parasitic and use animals as their host organism ; they need a vector to transfer them to their hosts (malaria - mosquitoes) or they can enter through polluted water - amoebic dysentery
Fungi
Eukaryotic organisms that are often multicellular (although yeasts are single celled) - fungi cannot photosynthesise and they digest their food extracellularly before absorbing the nutrients. Many fungi are saprophytes which means they feed in dead and decaying matter - however some fungi are parasitic, feeding on living plants and animals ; these are the pathogenic fungi which cause communicable diseases
Fungal diseases on plants affect the leaves, preventing photosynthesis and so quickly kill the plant - when fungi reproduce they produce millions of tiny spores which can spread long distances (they can spread rapidly through crops) - cause starvation
How do pathogens damage host tissues directly?
Symptoms are caused by the damage pathogens do to tissues + the way in which the body of the host responds to the damage
How do viruses damage host tissue?
Take over the cell metabolism - viral genetic material gets into the host cell and is inserted into the host DNA ; virus then uses the host cell to make new viruses which burst out of the cell, destroying it and spreading to infect other cells
How to Protista take over cells?
They digest the cell and use the cell contents to reproduce (breaking open the cell) ; proctists which cause malaria are an example of this
How else can pathogens damage host tissues?
Produce toxins - most bacteria produce toxins that poison or damage the host cells in some way, causing disease. Some bacterial toxins damage the host cells by breaking down the cell membranes, some damage/inactivate enzymes and some interfere with the host cell genetic material so they cells cannot divide
Some fungi produce toxins which affect host cells and cause disease
Plant diseases repercussions
Cause starvation, economies may struggle and jobs lost - threaten ecosystems and entire species too
Ring rot
Bacterial disease of potatoes, tomatoes and aubergines chased by gram positive bacteria Clavibacter - damages leaves, tubers and fruit with no cure. Once bacterial ring rot infects a field it cannot be used to grow potatoes again for at least 2 years
Tobacco Mosaic Virus?
Virus that infects tobacco plants and 150 other species (tomatoes and peppers). Damages leaves, flowers and fruit and stunts growth - this reduces yields and can lead to total crop loss. Resistance crop stains are available but there is no cure
Potato blight (think Ireland)
Fungus like protoctista oomycete Infestans - hyphae penetrate host cells, destroying leaves and tubers and fruit - no cure but resistant strains and chemical treatments can reduce infection risk
Black Sigatoka
CAUSED BY FUNGUS
Attacks and destroys leaves
Hyphae penetrate and digest the cells - turning leaves black, if plants are infected it can reduce yield by 50% and resistant strains are being developed - fungicide (chemical that kills fungi) treatment can control the spread of the disease but there is no cure
Food security
Plant diseases threaten staple crops like rice - threatens food security and the survival of the population ; bananas are a cash crop for example (economically crucial)
Tuberculosis
Bacterial disease of humans, cows, pigs, badgers and deer caused by M.bovis - damages and destroys lung tissue and suppresses the immune system so body is more vulnerable to other diseases ; global rise of HIV/AIDS has had a big impact on the number of people suffering from TB because people who have AIDS are more likely to develop TB infections - TB is curable (antibiotics) and preventable (vaccination + living standards)
HIV and TB link
HIV weakens immune system - increasing the risk of TB
How to deal with TB affecting animals?
Very difficult to prevent them becoming re-infected from wildlife ; unsure how to control wildlife infection
Could cull the wildlife source (TB has been cut rapidly in cattle) - this must be done thoroughly or could lead to greater disease spread as animals are dispersed
Culling is not ethical and vaccination is better - however this is not easy and may not control spread of disease
Bacterial meningitis
Bacterial infection (streptococcus pneumoniae) of the meninges of the brain (protective membranes in the surface of the brain) which can spread into the rest of the body causing septicaemia (blood poisoning) and rapid death Mainly affects young children and teenagers with symptoms including red/purple rash that does not disappear when glass is pressed against it is a symptom of speicaemia Antibiotics will cure the disease if delivered early and vaccines can protect against some forms 10% die
HIV/AIDS
AIDS (acquired immunodeficiency syndrome) is caused by Human immunodeficiency virus which targets T helper cells in immune system - gradually destroys immune system so affected people are open to other infections like TB and pneumonia. Can also affect non%human primates - is a retrovirus with RNA genetic material
Contains reverse transcriptase - enzyme which transcribes RNA into single strand of DNA which interacts with the genetic material of the host cell ; virus is passed from one person to another via bodily fluids (unprotected sex/sharing needles/breast feeding)
No vaccine or no cure but anti retroviral drugs slow the profess of disease and give years of healthy life
Girls and women at high risk of AIDS - prominent in areas which practise FGM (female genitalia mutation) - same equipment is used many times it can spread infection - more vulnerable to the disease during intercourse if undergone FGM- SUB SAHARAN AFFICA IS THE WORST WITH 70% OF INFECTED GLOBALLY LIVING THERE ; SOCIAL AND ECONOMIC CONSEQUENCES
Influenza
Viral infection of the ciliates epithelial cells in the gas exchange system - kills them, leaving the airways open to secondary infection - can be fatal for young children/elderly with chronic diseases… many of these deaths are from secondary bacterial infections like Pneumonia
Affects mammals and birds
3 strains with A being the most virulent (harmful)
Flu viruses mutate regularly - but these are quite small so immunity is left over if it is caught again BUT sometimes there is a major antigen changes causing a flu epidemic as no antibodies are available - vulnerable groups are continually given a flu vaccine to protect against the changing strains… no cure
Malaria
Caused by the Protista plasmodia and spread by bites of infected mosquitoes (the vector) - plasmodium had a complex life cycle with two hosts (mosquitoes and people) ; they reproduce inside the female mosquito and she needs to take 2 blood meals to provide her with the protein before she lays her eggs - this is when Plasmodium is passed on to people and it invades red blood cells, liver and the brain Disease recurs (continues periodically) making people vulnerable to other infections No vaccine against malaria Preventative measures can be effective - key is to control the vector ; anopheles mosquitoes can be destroyed by insecticides and by removing the standing water where they breed ; mosquito nets and door screens + long sleeved clothing can prevent them from biting people and spreading disease
Ring worm
Fungal disease affecting mammals - differ fungi infect different species ; causes grey-white chest circular areas if skin ; anti fungal creams may be a cure and they are not damaging
Athlete’s foot
Human fungal disease - a form of human ring worm that browns on and digests the warm , moist skin between the toes causing cracking and scaling - anti fungal creams are an effective cure
Two main types of transmission?
Direct and indirect transmission
Direct transmission
Pathogen transferred directly from one individual to the other
Direct contact
Inoculation
Ingestion
Examples of direct contact
Kissing or any contact with bodily fluids of another person (bacterial meningitis/STIs)
Direct skin to skin - ring worm (thus athletes foot)
Microorganism from faeces transmitted on the hands - diarrhoeal diseases
Inoculation
Break in the skin - during sex (HIV/AIDS) Animal bite (rabies) Puncture wound (septicaemia)
Ingestion
Taking in contaminated food or drink or transferring pathogens to the mouth from the hands
Indirect transmission?
From one individual to the next indirectly
Fomites
Inanimate objects such as bedding, socks or cosmetics can transfer pathogens (athletes foot, staphylococcus infections)
Inhalation
Droplet infection - minute droplets of saliva and mucus are expelled from your mouth as you talk/cough/sneeze - if these droplets contain pathogens, when healthy individuals breathe the droplets in they may become infected (influenza/tuberculosis)
Vectors
Vector transmits communicable pathogens from one hones to another - not always animals (mosquitoes with malaria)
Water can also act as a vector of disease (diarrhoea diseases)
Transmission between animals and humans?
Bird flu strain can be passed from sheep to people - minimise close contact with animals and wash hands thoroughly can reduce infection rates ; people can also act as vectors of some animal diseases with fatal results (foot and mouth disease)
What can reduce the spread of communicable diseases?
Regular hand washing - most effective way
Improvements in living and working conditions (reducing overcrowding and ensuring good nutrition)
Disposal of both bodily and household waste effectively
Factors affecting the transmission of communicable diseases in animals?
Overcrowding living and working conditions
Poor nutrition
Compromised immune system (HIV/AIDS or needing immunosuppressant drugs after transplant surgery)
Poor disposal of waste (breeding sites for vectors)
Climate change - tropical diseases spread over wider area
Culture and infrastructure - traditional medical practises can increase transmission
Socioeconomic factors - lack of trained health workers and insufficient public warning when there is an outbreak of disease
Transmission of pathogens between plants
Can be direct or indirect - direct involved direct contact if a healthy plant with any diseased plant : ring rot, TMV, black Sigatoka and the potato blight
Indirect transmission - soil contamination
Infected plants often leave pathogens or reproductive spores from fungi/Protista in the soil ; this can infect the next crop. Examples include black Sigatoka spores/ring rot bacteria, TMV or spores of P.Infestans
Some pathogens can survive the composting process so the infection cycle can be completed when contaminated compost is used
Indirect transmission vectors
Wind - viral/fungal/bacterial spores may be carried on the wind ; P.Infestans form spores which are carried by the wind to other potato crops/tomato plants
Water - spores swim in the surface film of water on leaves/raindrop splashes carry pathogens and spores - P.Infestans swims over films of water on the leaves
Animals - insects and birds carry pathogens and spores from one plant to another as they feed ; insects such as aphids inoculate pathogens directly into plant tissues
Humans - pathogens and spores are transmitted by hands, clothing, fomites, farming practises and transporting crops around the world ; TMV survives for years on crops and ring rot survives on farm machinery etc
Factors affecting transmission of communicable diseases in plants
Planting varieties of crops that are susceptible to disease
Overcrowding increases likelihood of direct contact
Poor mineral nutrition reduces resistance of plants
Damp/warm conditions increase survival and spread of spores
Climate change - increased rainfall and wind promote the spread of diseases ; changing conditions allow animal vectors to spread to new areas and drier conditions reduces the spread of disease
How to prevent spread of communicable diseases?
Leave room between plants to minimise the spread if pathogens
Clear fields as thou funky as possible - remove all traces of plants from the soil at harvesting
Rotate crops (spores/bacteria will eventually die if no access to host plant)
Strict hygiene - washing hands/washing boots and sterilising storage sack/machines
Control insect vectors
Examples of barrier defences on plants?
Waxy cuticle, bark on tress and cellulose cell walls - act as barriers to prevent pathogens getting in
Plants do not heal diseased tissue - they seal it off and sacrifice if because they are continually growing meristems which can replace the damaged areas
How to recognise an attack (plants)?
THEY ARE NOT PASSIVE
Receptors in cells respond to molecules from pathogens or to chemicals produced when cellulose wall is attacked - stimulates the release of signalling molecules that switch on genes in the nucleus. This triggers cellular responses which include defensive chemicals, sending alarm signals to unaffected cells to trigger defences and physically strengthening the cell walls
What happens when plants are attacked by pathogens?
They rapidly set up extra mechanical defences - produce high levels of polysaccharide callose with Beta 1,3 and beta 1,6 linkages between glucose monomers (DRAW THIS)
