Non-bacterial pathogens
Viruses as pathogens
Viruses as pathogens
- Generally specific to a particular tissues
- Depends on the presence of antigenic markers
- Influenza
- Highly infectious
- Very short incubation period
- Mutates frequently
- Respiratory disease
- Transmission
- Zoonotic (animal passed on to humans)
- Droplet infection (directly onto another organism)
- Animal dropping
- Fomite (inanimate objects with droplets on)
- Mode of infection
- Infects ciliated epithelial cells
- RNA virus infects cell producing more virus particles which then cause the cell to lyse (this causes the symptoms)
- The cilli are responsible for clearing mucous with bacteria on, these being killed by the influenza it leaves the vector open to other infections (secondary infections)
- The influenza mutates so much that you can be reinfected the next year
- Treatment and control
- Anti-viral drugs may reduce the symptoms and speed recovery
- Antibiotics can be used to combat secondary infections
- Hard to develop a vaccine due to mutation rate
- Spreads so quickly due to people not staying in bed and exposing other people
- Vaccine is effective in first 48 hours
- Influenza has an incubation period of 24-96 hours
- Pathogenic effect (symptoms)
- Fever; shivering sweating
- Myalgia; pain in the body
- Exhaustion can last for 6-12 weeks
- Opportunistic secondary infections may take hold
- Cells wall of chitin and glucans
- Many fungi grow hyphae (long thread-like filaments)
- Parasites sometimes living in mutualistic symbiotic relationships (help one another)
- Stem rust fungus
- Wheat is the staple food in 97% of countries
- 25% of the worlds food supply
- Reduces yield by 50-80%
- Transmission
- The disease is transmitted when spores are carried to young crop plants
- The spores may be left on the soil after harvest
- Spores can be transmitted in the wind to nearby fields
- Mode of Infection
- When the spores land on the host plant they need water to germinate
- If there is water then hyphae emerges and penetrates the stomata
- This allows the fungi to access the internal tissues
- The hypha secretes enzymes which digest the plant and absorbs the nutrients
- The hyphae branch to form mycelium that feeds and grows
- Ideal conditions are 25-30 degrees and wet leaves (or irrigation)
- Using fertilisers help the fungus grow and not disturbing the soil leaves infected soil at the surface
- Controlling stem rust
- Bigger spaces between plants to reduce moisture and increase distance for spores to travel
- Reduce the application of fertilisers
- Use of earlier-maturing crops avoiding the time of maximum spread
- Remove any wild Berberis so part of the life cycle is interrupted
- Fungicides will control the growth of stem rust
- Pathogenic effects
- The disease appears after 7-15 days after infection
- Rusty red pustules that contain up to 100,000 spores
- Stem rust absorbs nutrients reducing yield
- The pustules break the epidermis making it harder to control transpiration
- The mycelium grows into vascular tissue interfering with the supply to the growing wheat grains
- Stem rust weakens the stems causing the plants to fall over in high winds and rain
- Wheat is the staple food in 97% of countries
- Unicellular eukaryotic organisms
- Generally live as parasites and Protozoas can be pathogens of plants and animals
- Reproduce sexually and asexually
- Malaria parasite (Plasmodium spp.)
- Parasites of the blood
- Affects 200 million people each year worldwide, killing 1 million of them
- Complex life cycle with two separate hosts
- Transmission
- The mosquito acts as a vector
- Transmission occurs when an infected mosquito takes a blood meal
- Transmission will occur in both directions
- The gametocytes from the human transfer to the mosquito
- The mosquito will transfer sporozoites into the humans blood
- Mode of infection
- The malaria parasite travels to the liver through the blood stream
- The parasite invades the blood cells reproducing asexually
- Every 48-72 hours the parasite bursts out of the blood cells, this continues in a cycle
- If some of the parasites from the cycle become gametocytes and are taken to the female mosquito during a blood meal
- Endemic disease
- Malaria is an endemic disease meaning it has be constantly present in a country or area
- The problems of treating any endemic disease are
- The disease is widespread so any eradication programme will cover a large area
- Difficult to track down and remove sources of infection
- Requires cooperation from numerous communities to treat
- Costs a lot of money to control
- Treatment of malaria
- Limited treatments for malaria; include quinine, chloroquinine and artemisinin but have to be given quickly after infection
- People travelling to areas with endemic malaria are advised to take anti-malarial medicines
- Malarial parasite is developing resistance to relatively cheap drugs
- Sure be treated with a combination of drugs
- Prevention and control of malaria
- Yet to be an economic vaccine
- It is hidden from the immune system which makes it harder to create a vaccine
- Avoiding contact with mosquitoes
- Have mosquito screens on doors and windows
- Sleep under mosquito nets (ideally impregnated with insecticide)
- Wear long sleeve clothes and cover skin as much as possible
- Preventing mosquitoes breeding
- The lifecycle of mosquitos takes place mainly in water
- Remove possible breeding sites (stagnant water)
- Proper disposal of sewage so that water is not left standing
- Biological control, seeding local water supplies with organisms that feed on mosquito larvae
- Chemical control – spray water sources with pesticides which kills the eggs
- Implications of malaria
- Social; people have to be persuaded to change their behaviour to reduce risks
- Economic; the treatment, control and prevention of endemic diseases all involve substantial economic investment. You have to weigh the benefits against the costs
- Ethical; treating the disease often raises ethical issues, there are issues of informed consent in medical trials and different countries have different cultures. It is good practice to explain risks and the process. It also important to consider who gets the vaccine first
- The role of the scientific community
- The validation of different approaches to the control of this disease
- Data is used by the WHO to produce guidelines
- Help with earlier diagnosis of the disease allowing anti-virals to be used
- More efficient diagnosis, allowing cheaper ways to diagnose the disease
- Guidelines for antibiotic use
- What things can be done to prevent the disease
- More efficient prevention against disease; nets
- Monitor resistance and creation of new drugs
- Pathogenic effect
- Bursting of red blood cells cause flu like symptoms
- The body’s response to the bursting blood cells leads to fever, sweating, shaking, muscle pains and headaches
- Long term damage to the liver and a reduction of blood count leading to anaemia
- Damage is amplified by HIV / AIDS