Viral Diseases
Viruses are not cells — they are much SMALLER THAN BACTERIA. They reproduce by INVADING LIVING CELLS and using the cell's machinery to make copies of themselves. The cell eventually BURSTS, releasing new viruses to infect more cells. This cell damage is what makes you feel ill. Viral diseases CANNOT BE TREATED WITH ANTIBIOTICS.
Measles
Pathogen: VIRUS
How it spreads: Inhalation of DROPLETS from COUGHS AND SNEEZES of an infected person.
Symptoms: A RED SKIN RASH and a FEVER. Measles can be SERIOUS OR EVEN FATAL if complications such as pneumonia or encephalitis develop.
Treatment: No specific cure — patients are ISOLATED and given supportive care (fluids, rest).
Prevention: Most young children are VACCINATED against measles using the MMR VACCINE (Measles, Mumps and Rubella).
HIV
Pathogen: VIRUS
How it spreads: Through SEXUAL CONTACT or EXCHANGE OF BODY FLUIDS such as blood (e.g. when drug users share needles).
Symptoms: Initially causes a FLU-LIKE ILLNESS. Without successful treatment, the virus attacks the body's IMMUNE SYSTEM. Late stage HIV infection is called AIDS, when the immune system is so damaged it cannot deal with other infections or cancers.
Treatment: Controlled with ANTIRETROVIRAL DRUGS — these stop the virus replicating so the immune system stays healthy.
Prevention: Using BARRIER CONTRACEPTION (condoms), NOT SHARING NEEDLES, and screening blood used in transfusions.
Tobacco Mosaic Virus (TMV)
Pathogen: VIRUS (a plant virus).
How it spreads: By CONTACT BETWEEN PLANTS, or carried on the hands and tools of farmers/gardeners.
Symptoms: A distinctive MOSAIC PATTERN OF DISCOLOURATION on the leaves. The discoloured areas cannot PHOTOSYNTHESISE properly, so the plant shows STUNTED GROWTH and reduced crop yield.
Treatment: No cure — infected plants are usually DESTROYED.
Prevention: Good field HYGIENE (cleaning tools, washing hands) and growing TMV-RESISTANT STRAINS of the crop.