Airborne disease

Airborne diseases can be spread via respiratory droplets expelled from the mouth and nose.

An airborne disease is any disease that is caused by pathogens and transmitted through the air. Such diseases include many that are of considerable importance both in human and veterinary medicine. The relevant pathogens may be viruses, bacteria, or fungi, and they may be spread through coughing, sneezing, raising of dust, spraying of liquids, or similar activities likely to generate aerosol particles or droplets. Strictly speaking airborne diseases do not include conditions caused simply by air pollution such as dusts and poisons, though their study and prevention may be related.

Overview

Airborne diseases include any that are caused and transmitted through the air. Some 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, though the rate of infection decreases sharply with the distance between the source and the organism infected.

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.^[1]

Many common infections can spread by airborne transmission at least in some cases, including: Anthrax (inhalational), Chickenpox, Influenza, Measles, Smallpox, Cryptococcosis, and Tuberculosis.

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.^[2] 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.

Causes

An airborne disease can be caused by exposure to a source: an infected patient or animal, by being transferred from the infected person or animal’s mouth, nose, cut, or needle puncture. People receive the disease through a portal of entry: mouth, nose, cut, or needle puncture.

Transmission

Airborne transmission of disease depends on several physical variables endemic to the infectious particle. 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 the droplets containing the infectious particles, as winds, or human behavior, sum up the factors influencing the transmission of airborne diseases.

• Climate and living area. Rainfall (number of rainy days^[3] being more important than total precipitation^[4][5]), mean of sunshine daily hours,^[6] latitude, altitude^[4] are characteristic agents to take in account when assessing the possibility of spread of any airborne infection. Furthermore, some infrequent or exceptional extreme events also influence the dissemination of airborne diseases, as tropical storms, hurricanes, typhoons, or monsoons.^[7] Climate conditions determine temperature, winds and relative humidity in any territory, either all year around or at isolated moments (days or weeks). Those are the main factors affecting the spread, duration and infectiousness of droplets containing infectious particles. For instance, influenza virus, is spread easily in northern countries (north hemisphere), because of climate conditions which favour the infectiousness of the virus but on the other hand, in those countries, lots of bacterial infections cannot spread outdoor most of the year, keeping in a latent stage.

UV is harmful to both viruses and bacteria. UV incidence can determine the survival of the infectious particles, so that in those territories with a higher average of sunshine daily hours, and closer to the equator, some particles lose their infectious ability. Infectious particles show and increased survival in the presence of UV light at higher relative humidity levels. It is thought to be due to the protective effect of larger particle sizes, as evaporation would be less at these higher RH levels, showing a protective effect of a thicker water coat.^[8]

After isolated events, as tropical storms, has been determined that firstly the quantity of fungal spores is decreased, but a few days later, an exponentially increased number of spores is found, compared to normal conditions.^[9]

• Socioeconomics and living conditions. They have a minor role in airborne diseases transmission, but they also have to be taken in consideration. Dwelling is an important aspect. In cities the spread of diseases is faster than in rural areas and outskirts. Normally, cities enclose quarters of buildings, in which the transmission of the viral and bacterial diseases among the neighborhoods is uncomplicated. However, suburban areas are generally more favourable for higher airborne fungal spores^[8]

Nearness to large sources of water as rivers and lakes can be a cause of some outbreaks of airborne diseases, after changes in local watershed.^[7] Poor sewage systems are usually found in poor countries, especially in the rural areas, and can determine the proliferation of infectious bacteria, that once infecting animal or humans can be transmitted throughout the air.

Working conditions, can also settle infectious airborne diseases. At indoor environments, temperature and relative humidity are mainly affected by HVAC systems (heating, ventilation and air conditioning).^[10] Inadequate ventilation is implicated in the airborne transmission of respiratory viruses.^[3] Poor maintenance or defects on those systems can foster the conditions for airborne infections.^[11] For instance, a poor maintenance of air conditioning systems, can lead to an outbreak of Legionella (mainly Legionella pneumophila), that will spread among the population of the building (workers), before the finding of the focal point.^[12] In hospitals, isolation of patients sick of infectious diseases has to be added as a factor, which is noticeable in poor regions, where lack of resources facilitates the spread of infectious diseases.

Prevention

Some ways to prevent airborne diseases include washing hands, using appropriate hand disinfection, getting regular immunizations against diseases believed to be locally present, wearing a respirator and limiting time spent in the presence of any patient likely to be a source of infection.^[13] Exposure to a patient or animal with an airborne disease does not guarantee receiving the disease. Because of the changes in host immunity and how much the host was exposed to the particles in the air makes a difference to how the disease affects the body.^[13]

With few exceptions, antibiotics are not prescribed for patients to control viral infections. They may however be prescribed to a flu patient for instance, to control or prevent bacterial secondary infections. They also may be used in dealing with air-borne bacterial primary infections, such as pneumonic plague.^[14]

Additionally the Centers for Disease Control and Prevention (CDC) has told consumers about vaccination and following careful hygiene and sanitation protocols for airborne disease prevention.^[15] Consumers also have access to preventive measures like UV Air purification devices that FDA and EPA-certified laboratory test data has verified as effective in inactivating a broad array of airborne infectious diseases.^[16]

See also

• Vector (epidemiology)
• Waterborne diseases
• Zoonosis

References