Rabies antibody

Overview

Rabies antibody refers to the immune response generated against the rabies virus, either through natural infection or vaccination. These antibodies play a critical role in neutralizing the rabies virus, preventing it from infecting host cells, and thereby offering protection.

Two main types of rabies antibodies are measured:

1. IgM antibodies – indicate recent exposure or infection and are the first detected after vaccination or exposure.
2. IgG antibodies – provide long-lasting immunity, typically after vaccination or recovery from exposure.

Rabies antibodies can also be administered passively in the form of Rabies Immune Globulin (RIG) or human monoclonal antibodies, especially in unvaccinated individuals after a suspected rabid animal bite. These provide immediate but temporary immunity until the vaccine-induced immune response develops. Clinically, rabies antibody testing is important for diagnosis, post-exposure prophylaxis, confirmation of immune status, epidemiological studies, and travel requirements.

Symptoms

Rabies antibodies themselves do not produce symptoms, but their testing and presence are directly related to rabies infection or exposure. Symptoms prompting rabies antibody testing include:

1. Early Signs of Rabies Exposure:
   1. Pain, tingling, or itching at the bite or scratch site.
   2. Fever, headache, and general malaise.
2. Progressive Rabies Symptoms:
   1. Muscle spasms, anxiety, confusion, and agitation.
   2. Difficulty swallowing, hydrophobia (fear of water), and aerophobia (fear of drafts).
   3. Paralysis, hallucinations, and eventual coma.

Testing is also performed to evaluate vaccine response, especially in individuals with occupational exposure, travelers, or those who received post-exposure prophylaxis.

Causes

The presence and detection of rabies antibodies are caused by:

1. Vaccination:
   1. Following rabies vaccination, the body produces IgM and IgG antibodies to ensure protective immunity.
2. Passive Immunization:
   1. Administration of Human Rabies Immunoglobulin (HRIG) or Equine Rabies Immunoglobulin (ERIG) provides immediate antibodies to neutralize the virus in unvaccinated individuals.
   2. Human monoclonal antibodies such as Rabishield and Twinrab™ are newer alternatives for passive immunization.
3. Natural Infection:
   1. Rabies virus exposure through animal bites (dogs, cats, monkeys, rabbits) can stimulate antibody production.
4. Laboratory Detection Methods:
   1. IgM-ELISA is most sensitive for early detection.
   2. IgG-ELISA, virus neutralization tests, and RFFIT (Rapid Fluorescent Focus Inhibition Test) confirm long-term immunity or vaccine response.

Risk Factors

Certain individuals are at greater risk of rabies exposure and therefore require rabies antibody monitoring:

1. Animal Bite Victims: Especially from suspected rabid animals such as dogs, cats, bats, or monkeys.
2. Unvaccinated Individuals: More vulnerable to infection and often require RIG in addition to vaccination.
3. Veterinarians, Animal Handlers, and Laboratory Workers: At higher occupational risk.
4. Travelers to Rabies-Endemic Areas: Require vaccination and antibody monitoring for adequate protection.
5. Children: More likely to have unnoticed or severe exposures.
6. Immunocompromised Patients: May show weaker antibody responses and need closer monitoring.
7. Geographical Factors: Living in regions where rabies is endemic or where vaccination programs are weak.

Prevention

Prevention of rabies through antibody-based strategies includes both vaccination and timely medical care:

1. Vaccination:
   1. Pre-exposure vaccination for high-risk groups.
   2. Post-exposure prophylaxis combining rabies vaccine and RIG for unvaccinated individuals.
   3. Booster doses if antibody levels fall below the WHO-recommended 0.5 IU/mL threshold.
2. Testing and Monitoring:
   1. Rabies antibody titers are tested to confirm protective immunity.
   2. Methods include RFFIT, ELISA, and Virus Neutralization Tests (VNT).
3. Sample Collection:
   1. 3 mL of blood collected in a plain (red-capped) tube, with serum separated promptly.
4. WHO Guidelines:
   1. A titer of ≥0.5 IU/mL indicates adequate protection.
   2. Booster doses are recommended for those at continued high risk if levels drop below this threshold.
5. Animal Control and Public Health Measures:
   1. Vaccination of domestic animals, stray animal management, and public awareness campaigns reduce rabies exposure risk.