Infectious Diseases: Modes of Transmission

This document outlines the different modes of transmission for four significant infectious diseases: cholera, malaria, tuberculosis (TB), and HIV. Understanding these transmission routes is crucial for developing effective prevention strategies.

Cholera

Transmission

Cholera is primarily transmitted through the fecal-oral route. This means the bacteria, Vibrio cholerae, are ingested via contaminated food or water.

• Contaminated Water: Drinking water contaminated with human feces is a major source of infection.
• Contaminated Food: Food that has been handled by infected individuals or grown in contaminated water can also transmit the bacteria.
• Shellfish: Eating raw or undercooked shellfish from contaminated waters is a risk.

The bacteria are highly motile and thrive in aquatic environments, making water a common reservoir.

Malaria

Transmission

Malaria is a parasitic disease transmitted by the bite of infected Anopheles mosquitoes. The transmission cycle involves the mosquito, the human host, and the Plasmodium parasite.

1. Mosquito Bite: An infected female Anopheles mosquito bites a human and injects Plasmodium sporozoites into the bloodstream.
2. Liver Stage: The sporozoites travel to the liver and multiply asexually.
3. Blood Stage: The liver cells rupture, releasing merozoites into the bloodstream. These merozoites infect red blood cells, multiplying within them.
4. Mosquito Infection: When another Anopheles mosquito bites an infected human, it ingests blood containing merozoites. The merozoites develop into sporozoites in the mosquito's salivary glands.

The transmission is therefore a complex cycle involving both a biological vector (the mosquito) and a parasite.

Tuberculosis (TB)

Transmission

Tuberculosis is a bacterial infection primarily transmitted through the airborne route. Mycobacterium tuberculosis bacteria are released into the air when infected individuals cough, sneeze, speak, or sing.

• Airborne Droplets: The bacteria are carried in small droplets or particles that can remain suspended in the air for extended periods, especially in poorly ventilated spaces.
• Inhalation: When a susceptible person inhales these droplets, the bacteria can infect the lungs.
• Close Contact: Close and prolonged contact with individuals who have active TB disease increases the risk of transmission.

TB is often associated with crowded living conditions and inadequate ventilation, which facilitate the spread of the bacteria.

HIV

Transmission

HIV (Human Immunodeficiency Virus) is transmitted through specific bodily fluids: blood, semen, vaginal fluids, rectal fluids, and breast milk. The virus attacks the immune system, leading to AIDS (Acquired Immunodeficiency Syndrome).

Mode of Transmission	Description
Sexual Contact	Unprotected vaginal, anal, or oral sex with an infected person.
Blood Transfusion	Receiving contaminated blood or blood products. This is rare in countries with stringent screening procedures.
Sharing Needles	Sharing needles or syringes used for injecting drugs.
Mother to Child (Vertical Transmission)	From an HIV-positive mother to her child during pregnancy, childbirth, or breastfeeding.
Other bodily fluids	Less common, but can occur through cuts, wounds, or sharing other bodily fluids.

It is important to note that HIV is not transmitted through casual contact such as shaking hands, hugging, sharing food or drinks, or through saliva alone.