Pathogen Pathways

💨 Airborne Transmission

This route involves infectious agents spread via droplet nuclei—residue from evaporated droplets that can remain suspended in the air for extended periods. These agents can survive outside the body and infect others through the respiratory tract.

Particles are typically smaller than 5 µm. Examples include tuberculosis, chickenpox, and measles.

💧 Droplet Transmission

Generated by coughing, sneezing, or talking, these are larger, usually wet particles (> 5 µm) that travel shorter distances and typically contaminate susceptible mucosal surfaces (eyes, nose, mouth) in the presence of the host.

This is a common route for respiratory infections like influenza and coronaviruses. Masks can reduce droplet spread.

👋 Direct Contact

Transmission occurs through direct physical contact, including skin-to-skin contact, kissing, and sexual intercourse. It can also involve contact with soil or vegetation harboring infectious organisms.

Diseases like athlete's foot, impetigo, and syphilis are often transmitted this way.

🧼 Indirect Contact

This involves transmission through contaminated inanimate objects, known as fomites. Examples include touching contaminated surfaces, bedding, or surgical instruments.

Food and water can also act as vehicles, especially when sanitation and hygiene are compromised, leading to fecal-oral transmission.

💩 Fecal-Oral Route

Pathogens in fecal particles are transferred to another person's mouth. This route is heavily influenced by sanitation and hygiene practices. It can occur via contaminated food or water, or directly through contact with feces or contaminated body parts.

Common in areas with poor sanitation, leading to diseases like cholera and hepatitis A.

🦟 Vector-Borne Transmission

An organism, the vector, transmits pathogens without causing disease itself. Vectors can be mechanical (passive carriers, e.g., flies) or biological (harboring pathogens, e.g., mosquitoes, ticks).

Biological vectors are crucial for diseases like malaria, Lyme disease, and viral encephalitis.

💉 Iatrogenic & Needle Sharing

Iatrogenic transmission results from medical procedures, contaminated equipment, or injections. Needle sharing, particularly among intravenous drug users, is a significant route for blood-borne diseases like HIV and Hepatitis C.

👶 Vertical Transmission

Pathogens are passed from parent to offspring. This can occur in utero (prenatal), during childbirth (perinatal), or through postnatal contact like breastfeeding (transmammary transmission).

HIV, hepatitis B, and syphilis are examples of infections transmitted vertically.

👁️ Disease Surveillance

Monitoring the transmission of infectious diseases is known as disease surveillance. Traditionally, public health agencies rely on healthcare workers and labs to report cases of notifiable diseases.

Analyzing aggregate data helps understand disease spread, forming the core of epidemiology.

💻 Modern Tracking Methods

Beyond traditional methods, innovative approaches are used. These include analyzing insurance data, antimicrobial drug sales, and even patterns in web search queries (e.g., for influenza or dengue). Mobile phone data can also track population movements to predict disease spread.

Computer simulations and AI are increasingly employed to model and predict transmission dynamics.

🌱 Symbiotic Transmission

Transmission is also critical for beneficial microbial symbionts. Organisms can acquire symbionts from parents (vertical transmission) or the environment/unrelated individuals (horizontal transmission).

Examples include nutritional symbionts in insects and the human microbiome acquired during birth and breastfeeding.

🔄 Mixed-Mode Transmission

Many symbionts utilize both vertical and horizontal transmission. This mixed-mode transmission allows flexibility, enabling infection of offspring when host density is low and broader infection when hosts are abundant.

This can complicate predicting the exact benefit or harm these symbionts provide to their hosts.

📜 References