Pertussis IgA, IgG & IgM Antibodies

Overview

Pertussis, commonly known as whooping cough, is a highly infectious disease caused by Bordetella pertussis or Bordetella parapertussis, both aerobic Gram-negative bacteria that colonize the nose, throat, and respiratory tract. It spreads through respiratory droplets generated by coughing or sneezing.

The body mounts a serological immune response within about two weeks of infection, producing different classes of antibodies:

1. IgA antibodies protect mucosal tissues by neutralizing and agglutinating pathogens, preventing their attachment to respiratory surfaces.
2. IgG antibodies appear later, indicating past infection or vaccination but are not useful for monitoring treatment or vaccine response.
3. IgM antibodies appear early, at the onset of symptoms, and are most useful for diagnosing acute or recent infection.

Detection is done using methods like ELISA, immunoblot assays, and agglutination tests. These antibodies provide essential information for diagnosis, post-vaccination studies, and epidemiological research.

Symptoms

Pertussis progresses through distinct stages, and antibody detection often correlates with clinical presentation:

1. Incubation period (5–10 days): No symptoms, but bacteria begin multiplying.
2. Catarrhal stage (1–2 weeks): Resembles a common cold, with runny nose, sneezing, mild fever, and occasional cough. Highly infectious stage.
3. Paroxysmal stage (weeks): Severe coughing fits followed by a characteristic “whooping” sound, difficulty breathing, cyanosis, and apnea (especially in infants).
4. Convalescent stage (weeks to months): Gradual recovery, though coughing may be triggered by respiratory infections or irritants.

Additional symptoms include watery eyes, fatigue, vomiting after coughing, and complications such as pneumonia or seizures in severe cases.

Causes

Pertussis infection and subsequent antibody production are caused by the following mechanisms:

1. Pathogen: Bordetella pertussis attaches to respiratory epithelial cells using adhesins like filamentous hemagglutinin (FHA), fimbriae, and pertactin.
2. Toxin production: Virulence factors including pertussis toxin (PT), adenylate cyclase toxin (ACT), and tracheal cytotoxin (TCT) damage the respiratory tract and interfere with immune defenses.
3. Immune response:
   1. IgA response develops at mucosal surfaces to neutralize toxins.
   2. IgM response indicates acute infection and recent exposure.
   3. IgG response develops later, suggesting past infection or vaccination.

Thus, antibody tests provide insight into the timing and stage of infection.

Risk Factors

Certain groups are at higher risk of developing pertussis and may show antibody responses detectable by serology:

1. Infants and young children: Particularly vulnerable to severe symptoms like apnea and cyanosis.
2. Unvaccinated individuals: Lack of DTaP or Tdap vaccination increases susceptibility.
3. Close contacts of infected patients: Family members, caregivers, or healthcare workers exposed to droplets.
4. Immunocompromised patients: Reduced immune defenses allow for more severe infections.
5. Pregnant women and newborns: Higher risk of complications; maternal vaccination is recommended to transfer protective antibodies.
6. Epidemiological exposure: Populations in areas with outbreaks or low vaccine coverage.

Risk increases if vaccination schedules are incomplete or if booster doses are missed.

Prevention

Prevention of pertussis relies on vaccination, supportive care, and timely treatment:

1. Vaccination:
   1. DTaP vaccine (diphtheria, tetanus, acellular pertussis) for infants and children.
   2. Tdap booster for adolescents and adults, including pregnant women to protect newborns.
2. Early Diagnosis and Treatment:
   1. Serological testing of IgA, IgG, and IgM antibodies supports clinical diagnosis.
   2. Macrolide antibiotics (erythromycin, azithromycin) reduce disease severity and limit spread if administered early.
3. Infection Control Measures:
   1. Isolate confirmed cases to prevent droplet transmission.
   2. Maintain proper hand hygiene and respiratory etiquette.
4. Awareness and Monitoring:
   1. Collect relevant clinical history, vaccination details, and onset of symptoms for accurate testing.
   2. Repeat borderline antibody tests after 10–14 days to confirm diagnosis.
5. Public Health Strategies:
   1. Epidemiological surveillance and post-vaccination monitoring help control outbreaks.

By combining antibody testing, vaccination, and preventive care, the risk of severe pertussis infection and community transmission can be significantly reduced.