3.4 - Bacterial, Protist & Fungal Diseases

Salmonella food poisoning

• Many bacteria are harmless or helpful, but a few are pathogens that cause disease.
• They often make you ill by producing toxins (poisons) that damage cells and tissues.

How salmonella spreads

• Salmonella is a bacterium that causes food poisoning.
• It is taken in by eating food contaminated with the bacteria, for example:
  • Poultry that carried the disease while alive
  • Food prepared in unhygienic conditions

Symptoms and control

• The toxins the bacteria produce cause fever, stomach cramps, vomiting, and diarrhoea.
• In the UK, most poultry are vaccinated against Salmonella to control its spread.
• Most people recover without treatment, but severe cases can be treated with antibiotics.

Gonorrhoea

• Gonorrhoea is a bacterial disease that is a sexually transmitted disease (STD) - it's passed on by sexual contact, such as unprotected sex.
• Symptoms are:
  • Pain on urinating
  • A thick yellow or green discharge from the vagina or penis

Controlling its spread

Its spread can be controlled by treating infected people with antibiotics and by using a barrier method of contraception such as a condom.

Treatment

• It was once easily cured with the antibiotic penicillin.
• Many strains are now resistant to penicillin, so rarer antibiotics have to be used instead.

Malaria

• Malaria is caused by a protist called Plasmodium - a single-celled parasite.
• It's spread from host to host by mosquitoes acting as vectors (organisms that carry a pathogen from one host to another without getting the disease themselves).

How malaria is spread

1. A mosquito feeds on the blood of an infected animal and picks up the protist.
2. When it next bites, it injects the protist into the blood of a new host.

Effects on the body

• Inside the body, the protist destroys red blood cells.
• In serious cases it also damages the liver.
• This causes recurrent episodes of fever, and malaria can be fatal.

Reducing the spread

• Stopping the mosquitoes breeding.
• Killing them with insecticides.
• Stopping them biting people, using mosquito nets and insect repellent.

Rose black spot

Rose black spot is a fungal disease of rose plants.

Symptoms

1. Purple or black spots develop on the leaves.
2. The affected leaves then turn yellow and drop off early.
3. With fewer leaves, the plant photosynthesises less and so grows poorly.

How it spreads and is treated

• Spread - Through the environment in water or by the wind.
• Treatment - Spraying with fungicides, and removing and destroying the affected leaves so the fungus cannot spread to other plants.