Parapertussis is a respiratory infection causing a prolonged cough illness, often mistaken for whooping cough, or pertussis. The two diseases share similar symptoms, leading to frequent confusion outside of clinical settings. Parapertussis is caused by a different bacterium and generally presents as a milder illness, though it still requires medical attention.
The Causative Agent and Disease Definition
Parapertussis is caused by the bacterium Bordetella parapertussis, a close relative of Bordetella pertussis. Both are highly contagious, Gram-negative coccobacilli that infect the ciliated cells of the respiratory tract. The key biological difference lies in the toxins they produce. B. parapertussis does not produce pertussis toxin, which is a primary virulence factor causing the most severe symptoms of whooping cough.
This lack of pertussis toxin contributes to the generally less severe nature of parapertussis. However, B. parapertussis still produces other virulence factors, such as adenylate cyclase-hemolysin, allowing it to colonize the respiratory tract. The infection is communicable and spreads through aerosolized droplets from the cough or sneeze of an infected person.
Symptoms and Clinical Progression
The clinical course of parapertussis typically begins with symptoms similar to a common cold, including a runny nose, sneezing, and a mild, non-productive cough. A low-grade fever may be present during this initial catarrhal stage, which usually lasts for one to two weeks before the cough worsens.
The cough then progresses into the paroxysmal stage, characterized by sudden, uncontrollable, and violent bursts of coughing. These intense fits can sometimes lead to a high-pitched whooping sound upon inhalation or cause vomiting. These severe symptoms occur less frequently and for a shorter duration than observed with pertussis.
The average duration of symptoms is significantly shorter compared to pertussis, though the prolonged cough can still last for several weeks. Young infants, particularly those under six months, are the most vulnerable group. In these patients, complications like apnea and cyanosis (a bluish discoloration of the skin due to lack of oxygen) can occur.
Differentiating Parapertussis from Pertussis
The two diseases are difficult to distinguish solely based on clinical presentation because they share the hallmark of a paroxysmal cough. Parapertussis is generally a milder disease, leading to fewer hospitalizations and complications, especially in older children and adults.
A critical difference is their relationship with the standard pertussis vaccine. The DTaP or Tdap vaccines are formulated specifically to protect against B. pertussis by targeting its specific antigens.
The current acellular pertussis vaccines offer little to no cross-protection against B. parapertussis infection. This means fully vaccinated individuals can still contract parapertussis. In highly vaccinated populations, a significant portion of whooping cough-like illnesses may actually be caused by B. parapertussis.
Diagnosis and Treatment Protocols
Diagnosis relies on laboratory testing because symptoms alone are not specific enough to differentiate parapertussis from pertussis or other respiratory infections. The preferred method for confirmation is Polymerase Chain Reaction (PCR) testing performed on a nasal swab sample. Multi-target PCR assays can specifically detect genetic elements unique to B. parapertussis, distinguishing it from B. pertussis.
Treatment for parapertussis is largely supportive, focusing on managing symptoms, such as ensuring adequate hydration and rest. Antibiotics, typically macrolides, may be prescribed, but their ability to lessen the severity or duration of the cough is limited if started late in the illness.
The primary reason for administering antibiotics is to reduce the patient’s contagiousness and prevent the spread of the bacterium. Antibiotic treatment is recommended for infants and individuals in close contact with vulnerable populations to reduce transmission risk. The communicable period ends after five days of appropriate antibiotic treatment or after three weeks of coughing if no treatment is given. Unlike pertussis, post-exposure prophylaxis is generally not recommended for contacts of parapertussis cases.