Respiratory System Diseases

Infectious Diseases Affecting the Respiratory System

Respiratory Infection Classification

Many common respiratory infections with diverse causative agents present with similar symptoms that are classified based on what areas are inflamed.

There are many types of respiratory system infections, and they may affect the upper or lower respiratory system. Most respiratory conditions are characterized by the tissue that becomes inflamed during infection. Rhinitis is inflammation of the mucous membranes in the nose and presents with itchy, watery eyes; sneezing; and sore throat. Sinusitis is inflammation of the sinuses, the cavities around the nose, causing facial pain and pressure. Otitis is the inflammation of the ear that typically presents with pain and is caused by various ear infections. Laryngitis is the inflammation of the larynx, or voice box, and can make speaking difficult. The tonsils are two lymph nodes located on either side of the back of the throat. When they are inflamed the condition is called tonsillitis and is often accompanied by throat pain.

In the lower respiratory system, bronchitis is inflammation of the lining of the bronchial tubes and is accompanied by shortness of breath and coughing up thick mucus. Pneumonia is an infection that inflames air sacs in the lungs and is accompanied by cough with mucus, fever, and trouble breathing. Pneumonia is identified through anatomical diagnosis, or diagnosing a disease based on the symptoms and effects rather than the specific microorganism that causes it. Pneumonia is characterized by a severe inflammatory response in the lungs centered around the alveoli. This type of response manifests as catarrhal inflammation, in which inflamed mucous membranes produce large amounts of mucus that is frequently coughed up and can cause difficulty breathing, in addition to fever, chills, and chest pain.

Each type or category of infection may present singly or in combination with others; for example, rhinitis can be accompanied by sinusitis. Bacteria, viruses, and fungi may cause respiratory infections, and generally the type of disease is categorized based on symptoms of the infected tissues. The common cold, for example, while generally characterized by a fairly uniform series of symptoms, is caused by a wide variety of viruses. Viruses are biologically active particles made up of a nucleic acid genome and a protein coat that reproduce by invading the cells of living organisms and using the host’s cellular machinery to cause disease. Many respiratory pathogens exploit host defense mechanisms such as coughing and sneezing in order to pass from person to person by dispersing through droplets of saliva and mucus. Most respiratory infections are followed by a convalescent period, the period of time during illness when an infected person begins to feel better but is still contagious. The ability of respiratory diseases to spread by droplets (microscopic particles suspended in air) makes preventing the spread of disease very difficult during the convalescent period.

Symptoms of Pneumonia

Pneumonia is a complex disease with many different tissues affected and can be caused by a broad variety of pathogens.

Respiratory Disease Vaccines

Vaccines protect against infection by causing the immune system to proactively develop antibodies against a pathogen before it is ever encountered. Several vaccines are available to prevent respiratory infections.

Most common infections of the upper respiratory tract are fairly short, lasting from a few days to a couple of weeks. Other pathogens are capable of causing much longer-lived and more serious diseases. A major human accomplishment of the 20th century was the development of vaccines that protect against serious infectious diseases. Vaccines are substances given to individuals that stimulate their immune systems to produce antibodies against antigens presented by an infectious agent of disease. Based on the number of lives saved globally, several of the most successful vaccinations target respiratory system diseases. In regions of the world with modern medical establishments, children undergo a series of vaccinations through their early years. In general, vaccinations have been more successful at preventing bacterial infections than viral infections due to the rapid mutation and recombination rates of viral infections such as influenza. Because of its rapid rate of evolution, which strain of influenza—commonly called the flu—is going to spread during a given year is extremely difficult to predict. Epidemiologists and vaccine researchers frequently work together with the World Health Organization and the Centers for Disease Control and Prevention to predict which new strains of influenza virus will spread across the human population and to design vaccines to prevent deadly outbreaks. The influenza vaccine varies in its effectiveness due to variability in the ability of statisticians to predict the spread of the different variants. The influenza vaccine is also only effective for one to a few years. Since effectiveness wanes and the particular strains vary annually, individuals are encouraged to receive the influenza vaccine every year.

Vaccines are available to prevent several bacterial infections, and they are mostly effective for the lifetime of the patient. Bordetella pertussis is a species of gram-negative bacteria that is the causative agent of the disease pertussis, which is also known as whooping cough. Pertussis usually begins with cold-like symptoms but progresses to paroxysmal coughing—sudden fits of highly violent coughing that can cause vomiting, fainting, and broken ribs. The term paroxysmal refers to sudden resurgence of severe symptoms during infection. The severe cough that accompanies pertussis makes the disease highly contagious, and generally it lasts as long as 10 weeks.

Pertussis is extremely dangerous in babies and can cause apnea, a pause in breathing. Babies are not vaccinated for pertussis immediately, making them reliant on the rest of the population to be vaccinated, a property called herd immunity. Herd immunity occurs when a high enough proportion of individuals in a population are immune to a contagious disease that the disease is not able to spread or its spread is severely limited. The proportion of the population that requires vaccination to achieve herd immunity depends on the contagiousness of a particular causative agent. It only takes a few unvaccinated people to start the transmission of the disease again.

In order to prevent infection, most children in developed nations receive DTaP, a vaccine combination that protects against the diseases diphtheria, tetanus, and pertussis. The name DTap comes from the names of these three diseases. DTaP contains proteins isolated from B. pertussis that stimulate an adaptive immune response, which is an antigen-specific immune response. Children get five doses of the vaccine before age 7 and a final vaccine at 11. DTaP also protects against infection by Clostridium tetani, which causes tetanus, a bacterial infection causing muscle spasms, and Corynebacterium diphtheriae, a species of gram-positive bacteria that causes diphtheria, another respiratory disease. Diphtheria causes many symptoms that resemble a cold or the flu, such as fever and sore throat, but also causes severe swelling of the throat and neck that can make breathing and swallowing difficult. Other vaccines can prevent infections by certain strains of Streptococcus pneumoniae and Haemophilus influenzae serotype B, both common causes of pneumonia.