9 Airborne Microbial Diseases

Dr Gajendra Singh Vishwakarma and Dr. Sunil Mittal

Module 10 :Airborne Microbial Diseases

10.1 Introduction

10.2 Transmission factors

10.3 Air Borne Bacterial Diseases

10.3.1. Tuberculosis (TB)

10.3.2. Whooping cough

10.3.3. Meningitis

10.3.4. Pneumonia

10.4. Air Borne Viral Diseases

10.4.1. Chickenpox

10.4. 2. Influenza

10.4.3. Severe acute respiratory syndrome (SARS)

10.5. Air Borne Fungal Disease:

10.5.1. Aspergillosis

10.5.2. Cryptococcosis

10.1 Introduction

   Air is one of the most important abiotic components that supports life on earth. It contains oxygen which is one of the essential gas for human survival besides several other biotic and abiotic components. Out of these, some biotic and abiotic components are the major source of the several acute and chronic diseases for human and animals. The diseases that are transmitted and spread through the air are called air borne diseases. The pathogens enter the air through exhalation in the form of cough, sneeze, or talk, spewing nasal and throat secretions into the air of an infected person. The major contributor in the air borne diseases are the water droplets and dust particles that act as carriers for these pathogens. The pathogens settle down on these droplets and dust particles and travel distance along with air currents.

10.2 Transmission factors

The transmission of air borne disease depends upon the following factors.

1. Size of Droplets:

• Droplets larger than 100 µm fall to the ground quickly and get contaminated with dust. These may enter human body by inhalation or direct contact and may cause disease.
• Droplets smaller than 100 µm suspend in the air and travel over short distances depending on surrounding conditions.
• Very tiny droplets smaller than 5 µm stay within the atmosphere for a longer period of time and may travel longer distances after settling on the particulate matter. These smaller droplets enter the human body mostly by inhalation and can easily penetrate in the respiratory tract via crossing various filtration check points of the respiratory system.

2. Duration of exposure

The chances of infection increase with the duration of exposure to an airborne pathogen. In other words, people who are in closeness to an infected person over a long period of time are at greater risk than those who have very limited contact with the source. The people associated with the healthcare departments and hospitals are at particular risk.

3. Other factors

Other factor can also affect the probability of contracting the infection.

• Unsanitary households
• Overcrowding/ Higher Population Density
• Susceptibility –The peoples belongs to the weakened immune system because of another illness or malnutrition. Air borne disease can be classified on the basis of the causative agents.

Classification:

The air borne diseases can be divided into 3 main types on the basis of the class of causative agent.

•  Bacterial
• Fungal
• Viral

10.3 Air Borne Bacterial Diseases

10.3.1. Tuberculosis (TB):

Tuberculosis is commonly called TB. The disease is contagious and spread from person to person through air. When any infected person coughs or sneezes, nearby people may get infected by inhaling bacteria through breathing. Although, the bacteria can attack any part of the body, but it most commonly stick to the lungs and causes TB of lungs.

Causative Agent: The causative agent is Mycobacterium. Although 8 mycobacterial species (M. tuberculosis, M. bovis, M. africanum, M. microti, M. caprae, M. pinnipedii, M. canetti  and M. mungi) together make the M. tuberculosis complex and can cause TB, but Mycobacterium tuberculosis is the most common species found to cause disease in humans.

Symptoms of TB: The symptoms of TB depend on the infected part of the body. The main symptoms associated to the lung infected tuberculosis are:

• A bad cough continuously for two or more weeks
• Chest Pain
• Coughing up blood or sputum
• Weakness or fatigue
• Rapid loss of weight
• Loss of appetite
• Chills Fever
• Sweating at night

Transmission: M. tuberculosis is transmitted through airborne droplet nuclei of 1– 5 micro meters. Infectious droplet nuclei spread in the air through cough sneeze, shout, or sing of person already suffering from pulmonary or laryngeal TB. Depending on the environmental conditions, these tiny particles may persist in the air for several hours. Transmission occurs when these M. tuberculosis containing droplets enter in the mouth or nasal passages, adhere in the primary respiratory tract and finally reach to the bronchi and alveoli of the lungs.

Incubation Period: The incubation period of M. tuberculosis may vary from 2 to 12 weeks. A person may remain contagious for a long time (as long as viable TB bacteria are present in sputum) and during the time of medication up to several weeks. However, some infected people may suppress the infection and show the symptoms after some years; or some never develop any symptoms or become contagious.

Diagnosis: The diagnosis of TB can be done using various imaging techniques and chemical testing like skin, sputum and blood test. The imaging technique involves chest X-ray or a CT scan. The latent tuberculosis diagnosis carried out by the skin test (Mantoux tuberculin skin test or the tuberculin skin test or TST) is the most common test. The test involves tuberculin injection in skin at arm which is made from killed mycobacterium. In about 48-72 hours, the skin is examined for induration (swelling test) by a qualified person; a positive swelling means the patient has been exposed to live mycobacterium either via infection or via vaccination; no swelling suggests the person tests negative for TB. The diagnosis of active tuberculosis is carried by the sputum culture or tissue biopsy methods. However, these methods may take time of few weeks due to the slow-growing nature of the bacteria. Similarly, blood tests may be used to confirm active tuberculosis. The examples of TB blood tests are QuantiFERON-TB Gold in-Tube test and T-Spot TB.

Treatment: The treatment of TB involves three phase. The first phase of TB treatment it to cure the patient. Second and third are to prevent the spread of TB, and to prevent the development of drug resistant TB. For the treatment of TB, there are more than twenty drugs available which are prescribed in the differing combinations in different circumstances. For the Active and multi drug-resistant tuberculosis bacterium, combination of drugs is required at the same time. The most common antibiotics used to treat tuberculosis include: Isoniazid, Rifampin (Rifadin, Rimactane), Ethambutol (Myambutol), Pyrazinamide. For the drug-resistant TB, a combination of antibiotics called fluoroquinolones and injectable medications, such as amikacin, kanamycin or capreomycin, are generally prescribed for 20 to 30 months. In some exceptional cases, the bacterium also developed resistance to these medications as well. BCG (Bacille Calmette-Guerin vaccine) vaccination is also used in some countries to reduce childhood infections.

Prevention and Precautions: The first step of TB prevention is to stop the transmission of TB from one person to another. This is can be done by proper identification of people with active TB and then curing them through the proper and timely medication. Further, since the person with pulmonary tuberculosis remains contagious up to 2 to 3 weeks hence these patients are kept in the isolation. If isolation is not possibl,e then some precautions are important to prevent spread. These include:-

• Isolation from crowded places like schools, college and markets.
• Covering of mouth and nose while coughing or sneezing.
• Adequate and careful disposal of tissues. Usually burning or disposal in sealed plastic bags is recommended.
• Avoid sharing of beds and rooms with un-infected persons

10.3.2. Whooping cough (Pertussis): Whooping cough is serious illness mainly found in babies, children, teens, and adults.

Causative Agent: It is caused by Bordetella pertussis, a gram negative, aerobic, coccobacillus bacterium.

Symptoms of Whooping cough: The disease usually starts with symptoms like mild cough, running nose, cold or fever. The early symptoms of running nose, cold, cough and fever generally remain constant throughout the course of the disease. Later-stage symptoms of disease after one to two weeks progression are frequent events of Paroxysms (fits), rapid coughs with a high-pitched sound like “whoop”, vomiting during or after coughing and fits, exhaustion (very tired) after coughing fits etc.

Transmission: The Bordetella pertussis transmission occurs through person to person contact via airborne droplets or by direct contact with throat or nasal discharges of infected one’s. The most common modes of transmission are coughing and sneezing.

Incubation period: The symptoms of whooping cough bacteria usually appear with in 5 to 10 days, though it can take as long as twenty days.

Diagnosis: The diagnosis of the diseases is difficult in its early stages because of its resemblance to a common cold or bronchitis. As the whooping cough bacteria aggregate in the respiratory secretions, the confirmed diagnosis may be carried by taking the nose and throat swabs. For further detection, imaging X-ray and blood tests may also be performed.

Treatment and Prevention: The disease is prevented by childhood vaccination of DTaP and adulthood booster dose of Tdap. Antibiotics are also available for the treatment of whooping cough. The effectiveness of these antibiotics is very high when given in the very early stages of the disease. Antibiotic treatment started after the disease is well established may be recommended to reduce the bacteria spreading but it may not reduce the severity of symptoms.

10.3.3. Meningitis: Bacterial meningitis is one of the serious and deadly diseases caused by air borne microbes. The disease is so severe that very few people recover from meningitis. Mostly infected persons suffer from the permanent disabilities such as brain damage, hearing loss, and learning disabilities.

Causative Agent: There are several types of bacteria that can cause meningitis. For example

• Streptococcus pneumoniae
• Group B Streptococcus
• Neisseria meningitidis
• Haemophilus influenzae
• Listeria monocytogenes

Transmission: Meningitis bacteria are transmitted among the people through air contaminated with respiratory and throat secretions. Generally, the close contact (for example, coughing or kissing) or lengthy contact with infected persons spread these bacteria. Symptoms: Meningitis symptoms include sudden event of fever, headache, and stiff neck. There are other symptoms, such as Nausea, Vomiting, Photophobia (increased sensitivity to light) Altered mental status (confusion).

Incubation period: According to the World Health Organization, the incubation period is between 2 to 10 days.

Diagnosis: Diagnosis of bacterial meningitis is through blood culture method. It examines the growth of microorganisms especially bacteria. The gram staining is performed for the identification of bacterial strain. Computerized tomography (CT) or magnetic resonance (MR) scans are also used for the detection of head swelling or inflammation. X-rays or CT scans of the chest or sinuses may also show infection in other areas that may be associated with meningitis.

Treatment and Prevention: Acute bacterial meningitis must be treated immediately with intravenous antibiotics. The immediate treatment provide safeguard from the complications such as swelling and enlargement of brain. The dose of antibiotics and their combinations depends on the type of infected bacterial species. Generally broad-spectrum antibiotics are recommended until the exact cause of the meningitis is detected.

10.3.4. Pneumonia: Pneumonia is an infection of the lungs with a range of possible causes. It can be a serious and life-threatening disease.

Causative Agent: It can be caused by bacteria, viruses, or fungi. Bacterial pneumonia is the most common type in adults. Streptococcus pneumonia is most common bacteria responsible for pneumonia. It can enter the lungs through inhalation.

Transmission: Pneumonia can spread by many ways. The bacteria that are commonly hosted in the child’s nose or throat reach to the lungs via inhalation. The infectious bacteria may also blowout in air droplets by cough or sneeze. In addition, pneumonia may also infect blood shortly after birth. The research is very limited on different pathogens causing pneumonia and the mode of their transmission, therefore the treatment and prevention of this disease is very critical.

Symptoms: The symptoms of bacterial pneumonia are:

• Cough with the aggregation of thick yellowish and green, or blood-tinged mucus
• Intense chest pain that become very painful when coughing or breathing
• Sudden onset of chills and shivering
• Body temperature 102-105°F or above
• Some other symptoms are:
  •  Headache and muscle pain
  •  Breathlessness or rapid breathing
  •  Fatigue
  •  Moist skin

Diagnosis: Diagnosis carried out by

• Chest sounds for the indication of heavy secretion of mucus.
• White blood cell count
• Blood culture
• Mucus,or a sputum culture test.
• Chest X-rays.

Treatment

Antibiotics are preferably used for the treatment of Pneumonia. The antibiotic commonly used is amoxicillin dispersible tablets.

Prevention

To reduce child mortality, prevention of pneumonia is an essential task for the health and childcare workers. Dense and frequent Immunization programmes against Hib, pneumococcus is the only and effective way to prevent pneumonia.

10.4. Air Borne Viral Diseases

10.4.1. Chickenpox: Chickenpox, (varicella), a viral disease is known for its itchy red blisters that appear all over the skin.

Causative Agent: The virus belongs to the herpes virus category. Exactly, Varicella zoster virus is responsible for this disease.

Transmission: This disease spread through inhaling the infected droplets resulting from coughing or sneezing by an infected person.

Symptom: The main symptom of chickenpox is skin irritation and red itchy rashes. The rashes further develop into fluid-filled blisters. It usually appears mainly on the face, chest, and back and then spreads to the rest of the body. Other symptoms include:

•  Loss of appetite
• Tiredness
•  Fever
• Headache

Treatment and Prevention

The best way to prevent chickenpox is to get the chickenpox vaccine. Children, adolescents, and adults should get 2 doses of chickenpox vaccine. Most people who get the vaccine will not get chickenpox. If a vaccinated person does get chickenpox, it is usually mild—with fewer red spots or blisters and mild or no fever. The chickenpox vaccine prevents almost all cases of severe disease.

Use non-aspirin medications, such as acetaminophen, to relieve fever from chickenpox.

Do not use aspirin or aspirin-containing products for chickenpox. The use of aspirin in children with chickenpox may induce the Reye’s syndrome, a severe disease that damage the liver and brain and can cause death.

10.4.2. Influenza: Influenza, or flu, is a respiratory related illness caused by a virus. Flu is highly contagious and is normally spread by the coughing and sneezing of an infected person. Although unpleasant, flu is rarely life-threatening.

Causative Agent:     It is caused by various types of influenza viral strains. Three types of influenza viruses are recognized: A, B and C. Type A is more common.

Transmission: Influenza viruses are spread from person to person primarily through large-particle respiratory droplet transmission (e.g., when an infected person coughs or sneezes near a susceptible person). Transmission via large-particle droplets requires close contact between source and recipient persons, because droplets do not remain suspended in the air and generally travel only a short distance (less than or equal to 1 meter) through the air.

Incubation period: The typical incubation period for influenza is 1—4 days (average: 2 days).

Symptoms: Confusing flu with a bad cold is common. Flu and cold symptoms may both include a runny/blocked nose, sore throat and cough.

Some symptoms of flu that are different from a heavy cold:

•  High temperature
•  Cold sweats and shivers
•  Headache
•  Aching joints and limbs
•  Feeling exhausted

Diagnosis: A number of flu tests are available to detect influenza viruses in respiratory specimens. The most common are called “rapid influenza diagnostic tests (RIDTs).” RIDTs  work by detecting the parts of the virus (antigens) that stimulate an immune response. These tests can provide results within approximately 10-15 minutes, but are not as accurate as other flu tests.

Treatments: As flu is caused by a virus, antibiotics cannot help, unless the flu has led to another illness caused by bacteria. Antivirals, such as oseltamivir (Tamiflu) and zanamivir (Relenza), may be prescribed in some circumstances.

Painkillers can alleviate some of the symptoms, such as headache and body pains.Some painkillers, such as aspirin should not be given to children under 12. Individuals with flu should stay at home, avoid contact with other people where possible, keep warm and rest, consume plenty of liquids.

10.4.3. Severe acute respiratory syndrome (SARS) (SARS corona virus)

The pathogenesis of SARS is highly complex, with multiple factors leading to severe injury in the lungs and dissemination of the virus to several other organs. The SARS corona virus targets the epithelial cells of the respiratory tract and results in diffuse alveolar damage.

Incubation Period: 2-7 days

Clinical Features: Initial symptoms are flu-like and may include lethargy, myalgia, cough, sore throat, fever and other nonspecific symptoms. The only symptom common to all patients is fever above 38 °C (100 °F). The shortness of breath and/or pneumonia may also be linked to SARS. This may ultimately develop to either direct viral pneumonia or first bacterial pneumonia.

Prevention and Treatment:

There is no vaccine for SARS to date and isolation and quarantine remain the most effective means to prevent the spread of SARS. Other preventative measures include:

• Avoiding contact with bodily fluids
• Wearing a surgical mask
• Washing the personal items of SARS infected person with hot and soapy water (eating utensils, dishes, bedding, etc.)
• Keeping the infected children away from school.

10.5. Air Borne Fungal Disease:

10.5.1. Aspergillosis

Aspergillosis is the name given to a wide variety of diseases caused by fungi of the genus Aspergillus. Fungal species of genus Aspergillus seem to be present both in the outdoor and indoor environment. It is responsible for the disease Aspergillosis and patient with weakened immune system. This fungus targets the lungs and also known to develop some allergic reactions.

Symptoms: Different types of aspergillosis affect the body in various ways. Different types of aspergillosis have different symptoms.

Allergic Bronchopulmonary Aspergillosis (ABPA) In allergic bronchopulmonary aspergillosis (ABPA), the fungus produces allergic reactions that cause the coughing and chest pain.

Invasive aspergillosis: This type of aspergillosis invades lung tissues and may further spreads to kidneys or brain. If invasive aspergillosis is not treated properly, it can cause infectious disease like pneumonia which can be life-threatening.

Diagnosis:

1. Blood tests for the detection of antibodies, allergens, and fungus molecules,
2. Chest X-ray.
3. CT scan of lungs and
4. Sputum stain and culture to examine of bronchial mucus.

Treatment: Antifungal medicine used for the treatment of all types of the illness. Oral or intravenous drugs such as voriconazole commonly used for the aspergillosis.

10.5.2. Cryptococcosis: It is cause by two species;  Cryptococcus neoformansand Cryptococcus gattii.

Transmission: The spores of the Cryptococcus neoformans and Cryptococcus gattii present in the air entered into the respiratory tract.

Symptoms:  Brain  enlargement,  Lung  infection,  Chest  pain,  Low-grade  fever,  dyspnea, weight loss, and malaise.

Diagnosis: Biopsy with fungal stains and cultures, Fungal culture, Cryptococcal serology, and Cryptococcal antigen testing.

Treatment: Antifungal drugs like Amphotericin B deoxycholate, Flucytosine commonly used for the treatment.

Preventions: C. neoformans is mostly grows on the bird droppings, especially pigeon droppings. Therefore people who have weak immune systems should avoid contact with birds and bird droppings contaminated sites.