Airborne diseases are illnesses spread by tiny pathogens in the air. These can be bacteria, fungi, or viruses, but they are all transmitted through airborne contact.

In most cases, an airborne disease is contracted when someone breathes in infected air.

And a person also spreads the disease through their breath, particularly by sneezing and coughing and through phlegm. These facts make controlling these diseases more difficult.

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

1-Diphtheria

Diphtheria is a serious bacterial infection, usually of the throat, caused by Corynebacerium diphtheriae. The throat infection may obstruct breathing and cause death.

> Corynebacerium diphtheriae is gram-positive, nonspore forming, club shaped, granular, rod shaped.

Pathogenicity: C. diphtheriae is an obligate extracellular parasite. It is not invasive and usually grows only in the human upper respiratory tract, where it produces a potent exotoxins.

The exotoxin can cause damage to other organs such as the heart, kidneys and nerves and can result in death.

There are many harmless non-toxigenic strains of C. diphtheriae which may be carried in the throat. If the strain is toxin producing, the exotoxin becomes fixed on tissues unless neutralized by circulating antitoxin.

Mode of transmission:

- Diphtheria is spread from person to person by droplets from the respiratory tract of a carrier or patient, or via the discharge from cutaneous lesions.

- The bacteria resists drying and contaminated articles may serve as a reservoir of infection. Transmission is increased in over-crowded and poor socio-economic conditions.

• Incubation period: usually 2–5 days, but 1–7 days

possible.

• Communicability: up to 2–3 weeks after the onset of

the disease, shorter if antibiotics are given.

Manifestations:

Pharyngeal and tonsillar diphtheria:

• Sore throat, which may be mild or severe.

• A false membrane forms in the throat spreading from the tonsils to the anterior pillars and uvula. The membrane may obstruct the airway.

- It is typically a dirty grey or grey-green colour when fully developed but may be white in the early stage of the disease. The edges of the membrane are slightly elevated and bleeding occurs when there is an attempt to remove it.

- It should not be scraped off as the toxin may be released and absorbed into the bloodstream.

- Also:

• Neck tissues may become swollen giving a “bull neck” appearance.

• Pulse rate is often rapid.

• Fever; moderate (38.5°–39° C) to high (39.5°– 40° C).

Nasal diphtheria:

- Symptoms include:

• Unilateral or bilateral nasal discharge, initially clear and later becoming bloodstained.

Laryngeal diphtheria:

• Usually spreads from pharynx to larynx.

• Hoarseness or loss of voice.

• Croupy cough.

• Cyanosis.

• Difficulty in breathing and eventually respiratory obstruction.

Non-respiratory diphtheria (cutaneous diphtheria)

• Problematic in tropical countries

• Usually appears on exposed parts, especially the legs

• Lesions start as vesicles and quickly form demarcated

and sometimes multiple ulcers.

Complications

- The potentially fatal indirect and direct complications of

diphtheria are due to the release of diphtheria exotoxin

into the circulating blood and lymphatic by the

organism.

- The exotoxin becomes fixed on tissues unless

neutralized by circulating antitoxin.

1- Direct complication:

• Laryngeal croup.

2- Indirect complications:

• Neurological: polyneuritis may affect the cranial or peripheral nerves. Cranial nerve lesions can cause paralysis of the soft palate and regurgitation of fluids. Paralysis of the diaphragm and limbs could also occur.

• Cardiovascular: the heart muscle may be involved (myocarditis) or other effects leading to disturbances of the conducting fibers of the heart

renal - proteinuria may be a sign of renal damage.

Secondary complications

• Pneumonia • Otitis media

Diagnosis - Cultures of C. diphtheriae from nose and throat swabs are tested for toxin production.

- Laboratory findings: A smear of the throat exudate when stained with a methylene blue dye shows the bacterial rods. The patient’s white blood cell count may be normal or slightly raised.

Methods of treatment - Immediate antitoxin must be given to the patient.

- Antibiotics are used to destroy toxin producing organisms and to shorten the period of infectivity. Penicillin is given, or if allergic to Penicillin, Erythromycin is used.

-Susceptibility to diphtheria can be detected by:

1- Schick test: intradermal injection of a minute amount of diphtheria toxin incites local inflammation, which reaches a maximum at about 5 days in individuals who are susceptible to diphtheria, that is who do not have circulating antitoxin. These individuals can be immunized actively by injection of toxoid. Two or three doses at monthly intervals usually suffice for primary immunization.

2- A booster injection: About a year later induces a secondary response, this injection is advisable to maintain maximum protection. Alum precipitated toxoid somewhat more effective and is most widely used.

2- Tuberculosis Definition - Tuberculosis is a disease caused by organisms classified as

Mycobacterium. It is gram-positive, acid fast bacteria, the cell wall contain large amount of lipids 20-60% of dry wt. of wall.

There are three main types: 1- Mycobacterium tuberculosis: the main cause of tuberculosis globally. 2- Mycobacterium bovis: causes disease in cattle and other animals, as well as in humans. 3- Mycobacterium africanum: occurs in Africa.

Modes of transmission - Mycobacterium bovis can be transmitted to humans from animals through the air, or indirectly by drinking contaminated milk. - Control of cattle TB and pasteurization of milk largely prevents bovine TB in humans, although the disease is still found in low-income countries.

- The most common cause of TB is from Mycobacterium tuberculosis and most of the reference within this manual will be to this form of infection.

- Human sputum is the most important source of Mycobacterium tuberculosis, which is spread through air by droplet infection from coughing, sneezing, or some other form of enforced expiration from the lungs, such as singing or shouting.

- The small droplets may be inhaled and are able to reach the alveoli; they may travel via the blood stream to distant sites where they may be reactivated later.

- Those whose sputum is found to be smear positive microscopically, have the potential to infect others in close contact and should be considered potentially infective until they have completed at least two weeks of treatment.

- Those whose sputum is found to be smear negative are unlikely to infect others.

Pathogenicity: • Tuberculosis disease takes many forms and nearly

any part of the body may be infected. In addition to pulmonary tuberculosis, osseous (bone and joints) tuberculosis, enteritis, peritonitis, meningeal tuberculosis and infection of the cervical glands.

Manifestations of TB - There are two main categories of TB: • pulmonary and • extra-pulmonary.

Extra pulmonary TB - TB can affect any organ of the body including: • upper respiratory tract; meninges; pericardium; lymph nodes;

arms and joints; urinary tract; genital tract; peritoneum; eyes; mouth, tonsils, tongue and skin. Swelling and/or pain in the affected area may be the presenting symptom.

Pulmonary TB - As stated earlier, pulmonary TB is the most significant form of the disease, as it can be infectious to others.

Symptoms Respiratory

• Cough Sputum

• Blood spitting - Chest wall pain

• Breathlessness - Localised wheeze

• Frequent colds

General

• Loss of weight - Fever and sweating

• Tiredness - Loss of appetite

Diagnosis of TB Disease

• Signs and Symptoms consistent with TB

• Chest X-ray • Clinical Judgment

• Bacteriology

– AFB smear microscopy

– Nucleic Acid Amplification Testing (NAAT)

– Culture and Identification

- Drug susceptibility testing (DST)

TB treatment Regimens

• TB Infection – LTBI treatment options

– 9 months isoniazid

– 4 months rifampin

– 3 months isoniazid plus rifapentine

• TB Disease – pulmonary, drug susceptible TB, 6- month standard regimen

– Intensive phase: 2 months isoniazid, rifampin, ethambutol and pyrazinamide.

– Continuation phase: 4 months of isoniazid and rifampin.

Immunization

- Immunization has a role in the prevention of TB.

- The vaccine used to prevent TB is Bacille Calmette- Guerin (BCG).

Controlled trials in several Western countries, where most children

are well nourished, have shown that BCG can give 80% protection

against TB for up to 15 years if administered before the first

infection.

- Other trials in the United States and India have failed to show such

benefit. A number of smaller trials in infants in poor countries have

shown protection against military TB and TB meningitis.

- The present WHO recommendation is that BCG should be given as a

routine to all infants (with a few exceptions such as AIDS) and BCG is

included in the Expanded Programmed of Immunization (EPI).

- Immunization against TB with BCG (in all persons more than three

months old) should only be carried out following a negative

tuberculin skin test.

Systemic Mycosis These infections result from inhalation of the spores

of dimorphic fungi that have their mold forms in the soil.

Within the lungs, the spores differentiate into yeasts or other specialized forms. Most lung infections are asymptomatic and self-limited. However, in some persons, disseminated disease develops in which the organisms grow in other organs, cause destructive lesions and may result in death.

Infected persons do not communicate these diseases to others.

COCCIDIOIDE HISTOPLASMA BLASTOMYCES PARACOCCIDIOIDES

A- COCCIDIOIDE Disease

- Coccidioides immitis causes coccidioidomycosis.

Properties

- C. immitis is a dimorphic fungus that exists as a mold in soil and as a spherule in tissue.

Transmission:

- The fungus is endemic in arid regions of the southwestern United States and Latin America.

- In soil, it forms hyphae with alternating arthrospores and empty cells. Arthrospores are very light and are carried by the wind. They can be inhaled and infect the lungs.

Pathogenicity:

- In the lungs, arthrospores form spherules that are large, have a thick, doubly refractive wall and are filled with endospores. Upon rupture of the wall, endospores are released and differentiate to form new spherules.

- The organism can spread within a person by direct extension or via the bloodstream.

- Granulomatous lesions can occur in virtually any organ but are found primarily in bones and the central nervous system (meningitis)

- Dissemination from the lungs to other organs occurs in people who have a defect in cell-mediated immunity.

- Most people who are infected by C. immitis develop a cell-mediated (delayed hypersensitivity) immune response that restricts the growth of the organism.

- One way to determine whether a person has produced adequate cell-mediated immunity to the organism is to do a skin test.

- In general, a person who has a positive skin test reaction has developed sufficient immunity to prevent disseminated disease from occurring. If, at a later time, a person's cellular immunity is suppressed by drugs or disease, disseminated disease can occur.

Clinical Diagnosis - Infection of the lungs is often asymptomatic and is

evident only by a positive skin test and the presence of antibodies.

- Some infected persons have an influenza like illness with fever and cough. About. 50% have changes in the lungs (infiltrates, adenopathy, or effusions) as seen on chest x-ray.

- 10% develop erythema nodosum or arthralgias. This syndrome is called "valley fever" or "desert rheumatism"; it tends to subside spontaneously.

- Disseminated disease can occur in almost any organ; the meninges, bone and skin are important sites.

- Women in the third trimester of pregnancy also have a markedly increased incidence of dissemination.

- Erythema nodosum (EN) manifests as red, tender nodules ("desert bumps") on extensor surfaces such as the shins. It is a delayed (cell-mediated) hypersensitivity response to fungal antigens and thus is an indicator of a good prognosis.

- EN is not specific for coccidioidomycosis; it occurs in other granulomatous diseases, eg, histoplasmosis, tuberculosis, and leprosy. In infected persons, skin tests with fungal extracts cause at least a 5mm induration 48 hours after injection (delayed hypersensitivity reaction).

- Skin tests become positive within 2-4 weeks of infection and remain so for years but are often negative in patients with disseminated disease.

Laboratory Diagnosis of Coccidioide:

- In tissue specimens, spherules are seen microscopically.

- Cultures on Sabouraud's agar incubated at 25 °C show hyphae with arthrospores.

- In serologic tests, [gM and IgG precipitins appear within 2-4 weeks of infection and then decline in subsequent months.

- Complement-fixing antibodies occur at low titer initially, but the titer rises greatly if dissemination occurs

Treatment:

- No treatment is needed in asymptomatic or mild primary infection.

- Amphotericin B (Fungizone) or itraconazole is used for persisting lung lesions or disseminated disease.

- Ketoconazole is also effective in lung disease.

- Fluconazole is the drug of choice for meningitis.

- Intrathecal amphotericin B may be required and may induce remission, but long-term results are often poor.

- There are no means of prevention except avoiding travel to endemic areas.

B- HISTOPLASMA

Disease

Histoplasma capsulatum causes histoplasmosis.

Properties of Histoplasma

- H. capsulatum is a dimorphic fungus that exists as a mold in soil and as a yeast in tissue.

- It forms two types of asexual spores:

(1) tuberculate macroconidia, with typical thick walls and fingerlike projections that are important in laboratory identification.

(2) microconidia, which are smaller, thin, smoothwalled spores that, if inhaled, transmit the infection.

Transmission:

- This fungus occurs in many parts of the world.

- It grows in soil, particularly if the soil is heavily contaminated with bird droppings, especially from starlings. Although the birds are not infected, bats can be infected and can excrete the organism in their guano.

- In areas of endemic infection, excavation of the soil during construction or exploration of bat-infested caves has resulted in a significant number of infected individuals.

- In several tropical African countries, histoplasmosis is caused by Histoplasrna duboisii. The clinical picture is different from that caused by H. capsulatum.

Pathogenicity:

- Inhaled spores are engulfed by macrophages and develop into yeast forms.

Clinical Diagnosis:

- In tissues, H. capsulatum occurs as an oval budding yeast inside macrophages.

The yeasts survive within the phagolysosome of the macrophage by producing alkaline substances, such as bicarbonate and ammonia, that raise the pH and thereby inactivate the degredative enzymes of the phagolysosome.

The organisms spread widely throughout the body; especially to the liver and spleen, but most infections remain asymptomaric and the small grantdomatous foci heal by calcification.

With intense exposure (eg, in a chicken house or batinfested cave), pneumonia may become clinically manifest.

Severe disseminated histoplasmosis develops in a small minority of infected persons, especially infants and individuals with reduced cell-mediated immunity, such as AIDS patients.

In AIDS patients, ulcerated lesions on the tongue are typica] of disseminated histoplasmosis. In immunocompetent people, EN can occur. EN is a sign that cell-mediated immunity is active and the organism will probably be contained.

Furthermore, the skin test can stimulate an antibody response and confuse the serologic tests.

The skin test is useful for epidemiologic studies, and up to 90% of individuals have positive results in areas of endemic infection.

Diagnosis:

- In tissue biopsy specimens or bone marrow aspirates, oval yeast cells within macrophages are seen microscopically.

- Cultures on Sabouraud's agar show hyphae with tuberculate macroconidia when grown at low temperature, eg, 25°C and yeasts when grown at 37°C.

- Tests that detect Histoplasma antigens by radioimmunoassay and Histoplasma RNA with DNA probes are also useful.

- An antibody titer of 1:32 in the CF test with yeast phase antigens is considered to be diagnostic. However, cross-reactions with other fungi, especially Blastomyces, occur.

- CF titers fall when the disease becomes inactive and rise in disseminated disease.

- The ID test detects precipitating antibodies (precipitins) by forming two bands, M and H, in an agar-gel diffusion assay.

- The ID test is more specific but less sensitive than the CF test.

Treatment:

- No therapy is needed in asymptomatic or mild primary infections.

- With progressive lung lesions, oral itraconazole is beneficial.

- In disseminated disease, arnphotericin B is the treatment of choice.

- In meningitis, fluconazole is often used because it penetrates the spinal fluid well.

- Oral itraconazole is used to treat pulmonary or disseminated disease, as well as for chronic suppression in patients with AIDS.

- There are no means of prevention except avoiding exposure in areas of endemic infection.

C- BLASTOMYCES Disease:

- Blastomyces dermatitidis causes blastomycosis, known as North American blastomycosis.

Properties of Blastomyces:

- B. dermariridis is a dimorphic fungus that exists as a mold in soil and as a yeast in tissue. The yeast is round with a doubly refractive wall and a single broad-based bud.

Transmission:

- Inhalation of the conidia causes human infection.

Pathogenicity:

- Infection occurs mainly via the respiratory tract.

- Asymptomatic or mild cases are rarely recognized.

- Dissemination may result in ulcerated granulomas of skin, bone, or other sites.

Laboratory Diagnosis:

- In tissue biopsy specimens, thick-walled yeast cells with single broad-based buds are seen microscopically.

- Hyphae with small pear-shaped conidia are visible on culture.

- The skin test lacks specificity and has little value. Serologic tests have little value.

Treatment:

- Itraconazole is the drug of choice for most patients.

- Amphotericin B should be used to treat severe disease.

- Surgical excision may be helpful.

- There are no means of prevention

D- PARACOCCIDIOIDES

Disease: -Paracoccidioides brasiliensis causes paracoccidioidomycosis,

also known as South American blastomycosis.

Properties of Paracoccidioides - P. brasiliensis is a dimorphic fungus that exists as a mold in soil and as a yeast in tissue.

- The yeast is thick walled with multiple buds, in contrast to B. derrnatitidis, which has a single bud.

Transmission:

- The spores are inhaled, and early lesions occur in the lungs.

- Asymptomatic infection is common.

- Alternatively oral mucous membrane lesions, lymph node enlargement, and sometimes dissemination to many organs develop.

Laboratory Diagnosis:

- In pus or tissues, yeast cells with multiple buds are seen microscopically.

- A specimen cultured for 2-4 weeks may grow typical organisms.

- Skin tests are rarely helpful.

- Serologic testing shows that when significant antibody titers (by immunodiffusion or complement fixation) are found, active disease is present.

Pathogenicity:

- This fungus grows in the soil and is endemic in rural Latin America. Disease occurs only in that region.

Treatment:

- The drug of choice is itraconazole taken orally for several months.

- There are no means of prevention.

Rickettsioses Diseases

Rickettsia is a bacteria which are obligate intracellular parasites, spread by arthropod vectors (lice, fleas, mites and ticks).

1- Coxiella burnetii differs from other rickettsia in that: - it is enclosed in a persistent vacuole during growth and

division.

- Six to ten daughter cells will form within a host cell before the cell ruptures and releases them.

- No arthropod vector.

- It caused Q fever.

Prevention:

- Avoid tick - infested areas.

- wear protective clothing and use repellants.

- Ticks are difficult to eradicate as they can survive for 4 years without feeding.

- Remove ticks carefully.

Transmission:

- Aerosol

• Parturient fluids 109 bacteria released per gram of placenta.

- Urine, feces, milk. - Direct contact.

- Fomites. - Ingestion.

- Arthropods (ticks).

- Person-to-person (rare):

• Transplacental (congenital).

• Blood transfusions.

• Bone marrow transplants.

• Intradermal inoculation.

• Possibly sexually transmitted.

Symptoms of acute disease:

- Flu-like, self limiting

- Atypical pneumonia (30 to 50%)

- Hepatitis

- Skin rash (10%)

- Other signs (< 1%) such as Myocarditis, meningoencephalitis, pericarditis.

- Death: 1 to 2%

Symptoms of chronic disease:

• 1 to 5% of those infected

- Prior heart disease, pregnant women, immunocompromised

• Endocarditis

• Other

- Granulomatous hepatitis

- Cirrhosis

- Osteomyelitis

• 50% relapse rate after antibiotic therapy.

Diagnosis:

- Serology (rise in titer) IFA, CF, ELISA, microagglutination.

- DNA detection methods (PCR).

- Isolation of organism

• Risk to laboratory personnel.

• Rarely done.

Treatment

- Doxycycline

- Chronic disease – long course (2 to 3 years of medication).

Immunity - Long lasting (possibly lifelong).