Introduction
Whooping cough, also known as pertussis, is a respiratory tract infection caused by the bacterium Bordetella pertussis. In earlier days before the development of a vaccine, it was viewed as an infantile disease that affected children, mainly between the ages of 1 and 9. In this age group, it manifests in three major phases, namely the catarrhal phase, the convalescent phase, and the paroxysmal phase. In current times, the disease affects children who have not yet completed the required number of vaccinations. Moreover, it can be contracted by adults whose immunity has faded or is highly immunocompromised. Rarely does pertussis cause death. However, the majority of reported cases occur among babies.
Description of Bordetella pertussis
Bordetella pertussis is the causative agent of whooping cough, and it is Gram-negative, encapsulated, rod-shaped, small (about 0.8 μm by 0.4 μm), and pathogenic coccobacillus. It belongs to the genus Bordetella and possesses a flagellum-like structure that is used for mobility (Murray et al., 2021). The bacterium is strictly aerobic, does not produce spores, and has a single arrangement. It was first discovered in 1906 by two researchers known as Bordet and Gengous. B. pertussis is characterized by several virulence factors that it produces: hemolysin, pertussis toxin, filamentous hemagglutinin, tracheal cytotoxin, fimbria, and pertactin (Murray et al., 2021). B. pertussis only affects humans, and research has shown that it evolved either from Bordetella bronchiseptica or a related ancestor.
Route of Infection
The disease is contagious and only infects humans. Airborne droplets from the respiratory mucous membranes of the infected individual are deposited in the nose, eyes, or mouth of a healthy individual (Murray et al., 2021). It spreads from one person to another through coughing or sneezing, or by coming into contact with infected nasal and throat discharges. Moreover, when people share breathing space, they are highly likely to contract the disease if the air they are breathing contains bacteria.
Pathogenesis
The bacterium is transmitted through airborne droplets from the respiratory systems of infected people. Research studies using animal models have shown that the progression of classic pertussis commences with the adhesion of the bacterium to the trachea and nasopharynx (Murray et al., 2021). After they enter the body, the bacteria colonize ciliated cells of the respiratory mucosa: they adhere to the ciliated epithelial cells of the bronchi and trachea (Melvin et al., 2014).
Pathogenesis is supported by the production of virulence factors, which include adhesion factors, surface structures, toxins, and iron-acquisition systems. Adhesion to the surfaces is possible because of the production of surface protein structures, including pertactin and filamentous hemagglutinin (Melvin et al., 2014). They attach themselves to the sulfatides that are located on the cilia of epithelial cells. The bacteria survive the host’s defense mechanisms such as antimicrobial peptides and mucociliary elimination. They can multiply rapidly and avoid clearance by inflammatory cells. Their incubation period is approximately between 7 and 10 days.
During the multiplication phase, they also produce toxins that serve several functions: tracheal cytotoxin hinders ciliary motion, dermonecrotic toxin initiates local necrosis, pertussis toxin interrupts cell function, and adenylate cyclase toxin obstructs the process of phagocytosis (Melvin et al., 2014). They do not cause invasion, as they are localized within the respiratory epithelium. The stoppage of ciliary motion is detrimental because the body is unable to clear debris from the lungs. This causes coughing, which might lead to the release of bacteria into the air and cause more infections.
During the catarrhal phase, the disease is characterized by the common cold, sneezing, watery eyes, mild fever, and a mild cough. This is the stage at which the disease is easily treatable. After 7-14 days, the disease enters the paroxysmal phase which is characterized by symptoms that include coughing fits, inspiratory whoops, and vomiting (Berkowitz & Jerris, 2016). Children might not show coughing symptoms but may struggle with breathing. In extreme cases, infants could stop breathing. This stage can last for between 1 and 10 days. The convalescent phase sets in with the advent of adaptive immunity, which clears bacteria from the body (Berkowitz & Jerris, 2016). However, the symptoms are still present and subside gradually over a month.
Detection
Whooping cough is usually detected by conducting a nasal aspirate, a swab test, or a blood test. Health care providers evaluate a patient’s history to determine if they have been exposed to pertussis. Nasal aspirate involves the collection of a mucus sample with a swab from the throat: a physician injects a saline solution into the patient’s nose and collects a sample through suction (Daniels & Sabella, 2018). A sample can also be collected from the nose or throat using a swab. A blood test is mainly used in the later stages of the disease and involves the collection of a blood sample from a vein in the arm. B. pertussis can be cultured on several mediums such as charcoal-horse blood agar and Bordet-Gengou medium.
Polymerase chain reaction (PCR) is also useful in the disease’s detection because of its ability to detect Bordetella DNA (Berkowitz & Jerris, 2016). Beginning of the third week of illness, antibodies appear in the blood, and their presence can be verified using an enzyme-linked immunosorbent assay (Daniels & Sabella, 2018). The presence of specific IgA is proof of infection by B. pertussis. In rare cases, the physician might ask for an x-ray to determine whether there is fluid in the lungs or any form of inflammation.
Treatment
Whooping cough is mainly treated using antibiotics. Early treatment is recommended to control and reduce the transmission of the disease, especially to close contacts. Physicians can administer an antimicrobial agent as a preventive measure for people who are in close contact with a patient (Daniels & Sabella, 2018). Individuals with whooping cough can infect others beginning from the onset of the catarrhal phase up to 5 days after the commencement of antimicrobial treatment. Many healthcare givers prefer to use macrolide erythromycin as the antimicrobial agent of choice because of its effectiveness (Dias & Raw, 2018).
The drug is administered 4 times daily, for a protracted period of two weeks. Unfortunately, the drug has uncomfortable side effects that could hinder the patient from completing the treatment regimen. Other macrolide agents that are effective and commonly used include azithromycin and clarithromycin (Dias & Raw, 2018). These drugs are resistant to gastric acid, have higher rates of absorption into tissues, and have a relatively longer half-life when compared to erythromycin (Dias & Raw, 2018). In that regard, the frequency of administration is lower, as they involve 1 or 2 daily doses for a period of between 5 and 7 days (Dias & Raw, 2018).
In infants that are 30 days older and less, azithromycin is the recommended drug. Treatment doses for infants who are less than 6 months old include 10mg/kg per day for 5 days while for those older than 6 months, the treatment regimen includes the administration of 10mg/kg on the first day, followed by 5mg/kg/day for 4 days (Dias & Raw, 2018). Adults receive larger doses: on day one, they take 500mg, followed by the administration of 250mg/kg for 4 days (Dias & Raw, 2018). The dosage of the various antibiotics used is different and depends on the age of the patient. Treatment decisions should be made based on clinical judgment because there is limited literature regarding the effectiveness of the aforementioned drugs.
Epidemiology
Data released by the World Health Organization (WHO) and members of the Global Pertussis Initiative have revealed that the incidence of whooping cough is still high: in a population of 100,000, between 370 and 1500 people have the disease. (Daniels & Sabella, 2018) According to Daniels & Sabella (2018), the rate of incidence in the United States is between 800,000 and 3.3 million cases annually. Pertussis can be described as an emerging disease because, despite the presence of vaccines and high rates of immunization, the disease is still widespread in the US (Sabbe & Vandermeulen, 2015). Reported cases have increased in the past two decades. Before the development of vaccines, pertussis was described as an infant disease (Daniels & Sabella, 2018). However, it is currently common among adolescents and adults.
Conclusion
Pertussis is a respiratory tract infection that is caused by the bacterium Bordetella pertussis: a Gram-negative, encapsulated, rod-shaped, small, and pathogenic coccobacillus. The disease is contagious and only infects humans. It spreads from one person to another through coughing or sneezing, or by coming into contact with infected nasal and throat discharges. The mouth, eyes, and nose are the main routes of infection. Diagnosis involves a nasal aspirate, a swab test, or a blood test. In some cases, detection is conducted through PCR. Treatment is mainly done using different types of antibiotics that are administered based on a patient’s age. Pertussis is an emerging disease, and it is still widespread despite the high number of immunizations.
References
Berkowitz, F. E., & Jerris, R. C. (2016). Practical medical microbiology for clinicians. WILEY Blackwell.
Daniels, H. L., & Sabella, C. (2018). Bordetella pertussis (pertussis). Pediatrics in Review 39(5), 247-257. Web.
Dias, W., & Raw, I. (Eds.). (2018). Pertussis: Disease, control and challenges. IntechOpen Limited.
Melvin, J. A., Scheller, E. V., Miller, J. F., & Cotter, P. A. (2014). Bordetella pertussis pathogenesis: current and future challenges. Nature Reviews Microbiology 12(1), 274-288. Web.
Murray, P. R., Rosenthal, K. S., & Pfaller, M. A. (2021). Medical microbiology (9th ed.). Elsevier Inc.
Sabbe, M., & Vandermeulen, C. (2015). The resurgence of mumps and pertussis. Human Vaccines & Immunotherapeutics 12(4), 955-959. Web.