The ways in which infectious diseases are transmitted are linked to the type of disease, for example, an airborne disease can be spread through indirect contact whereas something like HIV is transmitted directly through sexual contact. Factors that allow the spread of disease through both direct and indirect contact are food, water, soiled objects, sexual intercourse, skin or mucous membrane. These allow you to spread diseases from human to human and animal to human.
Infectious diseases are caused by microorganisms like bacteria, viruses, or parasites. How these diseases are transferred are through direct contact from human to human. For example, HIV is transmitted from person to person via bodily fluids. It cannot just be spread by touch or close proximity but require body fluids to enter the person. Ways it can be transferred is through sexual intercourse as unprotected sex allows an infected person to spread the virus directly through the transfer of sexual fluids. Those who already have STI (Sexually Transmitted Infection) are at a higher risk of contracting HIV. Another method on how this virus could be spread is through blood transfusion. For instance, a child of an HIV positive mother can contract the virus during the pregnancy, labour or through breastfeeding.
Zoonotic diseases are transmitted between animals and humans. An example of a disease which is spread by an animal to humans is rabies. Animals which can carry this disease are cats, dog or wild animals like foxes, bats and racoons. The rabies virus can be transferred from an infected animal biting a person or through infected saliva. The salvia containing the virus could enter into the human body through open wounds or any mucous membranes like the eyes, nose mouth. Wounds around the neck or head can allow the virus to travel quickly and easily to the brain. Hantavirus pulmonary syndrome is a rat-borne disease which is can be transmitted through direct contact with a rat, its faeces and urine. Similarly, lymphocytic choriomeningitis (LCMV) is a virus which is acquired through contact with mice droppings or urine. It can also be transferred through breathing contaminated dust.
Infectious diseases can be spread indirectly through the air or through other mechanisms. Some zoonotic infections are transmitted by vectors such as insects, particularly those that suck blood. These include examples like fleas, mosquitos, lice and ticks. The way in which these insects become infected is when they feed on infected hosts, like birds, animals, and humans. An example is Malaria which is transmitted by Anopheles mosquitoes. This mosquito feeds on an infected host which carries the Plasmodium parasite. It then undergoes a cycle of reproduction where the parasite migrates to the mosquito’s saliva gland. The way in which it transfers the parasite into humans is when the mosquito bites for a blood meal. The parasite is then able to escape into the bloodstream spreading the infection. This is the way in which malaria is transferred from vectors to humans.
Infections can be transmitted by touching surfaces and objects. This is because droplets during coughing and sneezing fall on to surfaces like doorknob and tabletops spreading germs. A common infection is Tuberculosis which is an airborne disease. It is spread when an infected person sneezes or coughs, releasing infectious droplets into the air. The droplets fall on the ground, surfaces and objects. This is easily transmitted to those who are in close proximity. If someone was to touch this surface the disease will be transferred through mucous membranes like the mouth allowing the bacteria to go inside the body infecting the individual allowing the spread of disease.
Infectious diseases can be transmitted via contaminated food and water. For example, the infection salmonellosis is caused by a bacteria called salmonella. This is found in the intestinal tract of animals. The way this is transmitted is through foods that have been contaminated by animal faeces. Commonly infected foods include raw meat, poultry and seafood. Faeces may get onto raw meat and poultry during the butchering process. Some fresh produce may be washed with water contaminated with salmonella. The consumption of this food leads to the spread of salmonella.