An airborne disease is any disease that is caused by pathogens that can be transmitted through the air over time and distance by small particles. Such diseases include many of considerable importance both in human and veterinary medicine. The relevant pathogens may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, toilet flushing or any activities which generate aerosol particles or droplets. Human airborne diseases do not include conditions caused by air pollution such as volatile organic compounds (VOCs), gases and any airborne particles.
Airborne transmission is distinct from transmission by respiratory droplets. Respiratory droplets are large enough to fall to the ground rapidly after being produced (usually greater than 5 μm), as opposed to the smaller particles that carry airborne pathogens. Also, while respiratory droplets consist mostly of water, airborne particles are relatively dry, which damages many pathogens so that their ability to transmit infection is lessened or eliminated. Thus the number of pathogens that can be transmitted through an airborne route is limited.
Airborne diseases include any that are caused via transmission through the air. Many airborne diseases are of great medical importance. The pathogens transmitted may be any kind of microbe, and they may be spread in aerosols, dust or liquids. The aerosols might be generated from sources of infection such as the bodily secretions of an infected animal or person, or biological wastes such as accumulate in lofts, caves, garbage and the like. Such infected aerosols may stay suspended in air currents long enough to travel for considerable distances; sneezes, for example, can easily project infectious droplets the full length of a bus.
Airborne pathogens or allergens often cause inflammation in the nose, throat, sinuses and the lungs. This is caused by the inhalation of these pathogens that affect a person's respiratory system or even the rest of the body. Sinus congestion, coughing and sore throats are examples of inflammation of the upper respiratory air way due to these airborne agents. Air pollution plays a significant role in airborne diseases which is linked to asthma. Pollutants are said to influence lung function by increasing air way inflammation.
Many common infections can spread by airborne transmission at least in some cases, including but not limited to: measles morbillivirus, chickenpox virus; Mycobacterium tuberculosis, influenza virus, enterovirus, norovirus and less commonly coronavirus, adenovirus, and possibly respiratory syncytial virus. Because the drying process often damages the pathogens, the number of diseases that can be spread through an airborne route is limited.
Airborne diseases can also affect non-humans. For example, Newcastle disease is an avian disease that affects many types of domestic poultry worldwide which is transmitted via airborne contamination. Often, airborne pathogens or allergens cause inflammation in the nose, throat, sinuses, and the upper airway lungs. Upper airway inflammation causes coughing congestion, and sore throat. This is caused by the inhalation of these pathogens that affect a person's respiratory system or even the rest of the body. Sinus congestion, coughing and sore throats are examples of inflammation of the upper respiratory air way due to these airborne agents.
Routes of transmission
Airborne infections usually occur by the respiratory route, with the agent present in aerosols (infectious particles <5 µm in diameter)." This includes dry particles, often the remainders of an evaporated wet particle called nuclei, and wet particles. This kind of infection usually requires independent ventilation during treatment. e.g., tuberculosis.
Environmental factors influence the efficacy of airborne disease transmission; the most evident environmental conditions are temperature and relative humidity. The sum of all the factors that influence temperature and humidity, either meteorological (outdoor) or human (indoor), as well as other circumstances influencing the spread of droplets containing infectious particles, as winds, or human behavior, influence the transmission of airborne diseases.
- Rainfall, the number of rainy days being more important than total precipitation; mean daily sunshine hours; latitude and altitude are relevant when assessing the possibility of spread of any airborne infection. Some infrequent or exceptional events influence the dissemination of airborne diseases, including tropical storms, hurricanes, typhoons, or monsoons.
Climate determines temperature, winds and relative humidity, the main factors affecting the spread, duration and infectiousness of droplets containing infectious particles. The influenza virus is spread easily in the Northern Hemisphere winter due to climate conditions which favour the infectiousness of the virus.
- After isolated weather events, the concentration of airborne fungal spores is decreased; a few days later, an exponentially increased number of spores is found, compared to normal conditions.
- Socioeconomics has a minor role in airborne disease transmission. In cities, the spread of airborne disease is more rapid than in rural areas and urban outskirts. Rural areas generally favor higher airborne fungal dissemination.
- Proximity to large bodies of water such as rivers and lakes can be a cause of some outbreaks of airborne disease.
- Hospital-acquired airborne diseases are associated with poorly-resourced medical systems, which make isolation challenging.
Some ways to prevent airborne diseases include disease-specific immunization, wearing a respirator and limiting time spent in the presence of any patient likely to be a source of infection. Exposure to a patient or animal with an airborne disease does not guarantee contracting the disease, as infection is dependent on host immune system competency plus the quantity of infectious particles ingested.
The United States Centers for Disease Control and Prevention (CDC) advises the public about vaccination and following careful hygiene and sanitation protocols for airborne disease prevention. Many public health specialists recommend physical distancing (also known as social distancing) to reduce the transmission of airborne infections.
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Airborne transmission occurs by dissemination of either airborne droplet nuclei or small particles in the respirable size range containing infectious agents that remain infective over time and distance
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