Measles

Measles is a viral disease that can cause fever and a red skin rash. It can be serious, and complications can sometimes be fatal.

An infected person releases droplets when they cough or sneeze. Another person can inhale these droplets, allowing the virus to enter their body and potentially cause infection.

Young children are commonly vaccinated against measles to protect them from the disease.

Tobacco mosaic virus

Tobacco mosaic virus (TMV) is a widespread plant pathogen: a virus that causes disease in plants. It infects many plant species, including tomato plants.

Infected leaves develop a distinctive mosaic pattern of discolouration. The affected leaves carry out less photosynthesis, so the plant makes less glucose for growth. As a result, the plant grows less.

Transmission of pathogens

A pathogen can spread when it is transferred from an infected host—a person or other organism carrying it—to another host. This transfer is called transmission. It can happen through direct contact or by an indirect route.

Direct contact

A pathogen can pass directly from one host to another when they touch. It can also be transmitted through the exchange of blood or other body fluids. For example, contact with infected blood can transfer a pathogen to another person.

Indirect transmission

In indirect transmission, something carries the pathogen between hosts. The main routes include:

• Contaminated surfaces: a person touches a surface carrying a pathogen and then transfers it to their body.
• Contaminated food: a person eats food containing a pathogen.
• Animals: an animal carries a pathogen and transfers it to another host, for example through a bite.
• Air: infectious droplets or particles enter the air and are breathed in by another person.

Transmission routes and prevention

Preventive actions depend on how a pathogen spreads. Cleaning surfaces and washing hands can reduce transmission by contact with contaminated surfaces. Safe food handling can reduce transmission through food, while protection from bites can reduce transmission by animals. Ventilation can reduce the concentration of infectious particles in the air. Avoiding contact with another person’s blood or other body fluids can reduce transmission by those routes.

HIV, AIDS and Antibiotics

HIV is a virus that infects helper T cells, which help coordinate immune responses by stimulating other immune cells. Over time, HIV reduces both the number of helper T cells and how well they function. As a result, other immune cells receive less stimulation, and the body's immune responses become weaker.

AIDS is the advanced stage of HIV infection. At this stage, the immune system is severely weakened, allowing opportunistic infections and other illnesses to cause serious symptoms. Opportunistic infections take advantage of the weakened immune system; they may be controlled more effectively when the immune system is functioning normally.

Why antibiotics do not treat HIV

Antibiotics act against bacterial structures or processes. Viruses do not have the bacterial targets on which antibiotics act, and they reproduce using the machinery of host cells. Antibiotics therefore do not treat HIV or other viral infections.

A person with AIDS can nevertheless develop a bacterial infection. Antibiotics may be used to treat that bacterial infection, but they do not treat the underlying HIV infection.

HIV transmission and control

HIV is a virus that attacks cells of the immune system, weakening the body’s ability to defend itself. It can be transmitted through sexual contact or through the exchange of certain body fluids. For example, sharing needles can transfer infected blood from one person to another.

After infection, HIV can initially cause a flu-like illness. The virus then continues to damage immune cells. If the immune system becomes severely damaged, the infection can progress to AIDS. At this stage, the body cannot deal effectively with other infections or some cancers.

Antiretroviral drugs control HIV by reducing the amount of virus in the body. This reduces damage to immune cells and helps prevent progression to AIDS.