🏥 Disease Spreading Game 🩺

Pathogen: an agent that causes disease. Exposure: contact with a possible source. Infection: establishment or multiplication of the agent in a host. Infectiousness: ability to transmit infection at a particular time.

Clinical example: exposure to an infected person does not guarantee infection; infection may occur without symptoms.

In this game: a particle may come close to an infectious particle, but transmission is probabilistic.

Incubation period: infection to symptom onset. Latent period: infection to becoming infectious. Infectious period: the time during which transmission can occur.

These are distinct. A person can become infectious before symptoms appear. The model's latent and infectious durations are simplified step counts, not disease-specific clinical estimates.

R₀ is the average number of secondary infections caused by an infectious person in a fully susceptible population under specified conditions. Rₜ is the corresponding average at a particular time, given current immunity, behaviour and interventions.

Values above 1 can support epidemic growth; sustained values below 1 generally indicate decline. These are population-level concepts—not the number of contacts of one particular person. Do not equate the game's observed average with a formal estimate of R₀ or Rₜ.

Transmissibility concerns spread. Severity concerns how ill people become. Virulence describes the capacity to cause harm. Mortality describes deaths in a population; the case-fatality ratio is deaths among identified cases over a specified period.

A disease that spreads widely is not automatically the disease with the highest fatality ratio.

Incidence concerns new cases over time. Prevalence concerns all existing cases at a point or over a period. Attack rate is commonly the proportion of an at-risk group that becomes ill during an outbreak; despite its name, it is usually a cumulative incidence proportion.

Endemic: usual or expected presence in an area or population. Epidemic: occurrence above what is expected. Pandemic: an epidemic spread across countries or continents, affecting many people. Outbreak: a cluster or increase in cases that warrants investigation; it is often used for a more localised event.

Transmission is often uneven: many infected people may transmit to few or no others, while a small number transmit to many. Overdispersion describes this extra variation. Crowding, timing, behaviour, environment and pathogen factors may contribute.

This game includes random variation, but it does not implement a validated disease-specific overdispersion model.

Population immunity can reduce the number of susceptible people and interrupt transmission chains. Vaccines differ in their effects on infection, infectiousness and severe disease. Protection may wane, and effectiveness varies by vaccine, pathogen and population.

Here, initially vaccinated particles are protected from infection for simplicity. This is an educational assumption, not a claim that any real vaccine gives complete protection.

Isolation separates people who are infected from others. Quarantine restricts movement or contact for people who may have been exposed, according to applicable public-health guidance. Contact tracing identifies and follows up people who may have been exposed.

The isolation switch in this model reduces movement and contacts for infectious particles. It does not model every practical or ethical consideration of isolation policies.

• Respiratory: inhalation of infectious aerosols and/or exposure to respiratory particles at close range, depending on the pathogen and setting.
• Direct or indirect contact: physical contact or contaminated objects/surfaces where relevant.
• Faecal–oral / waterborne: pathogens reach a new host through contaminated food or water.
• Vector-borne: a vector such as a mosquito transmits the pathogen.
• Zoonotic: transmission from animals to humans; some infections can then spread between people.

The animated engine here models simplified proximity-based respiratory transmission. Dengue needs a mosquito–human cycle; cholera needs a food/water contamination pathway. They should not be simulated with the same engine without those mechanisms.

Nipah is a zoonotic infection that can cause severe neurological and respiratory disease. Spillover may involve infected animals or contaminated food, and human-to-human transmission has been documented, including in healthcare settings.

For teaching, distinguish spillover, close-contact transmission, severity and the success of contact follow-up. This game's Nipah selection uses a lower illustrative contact-transmission probability; it is not calibrated to a particular outbreak and does not model animal or food exposure.

Use current WHO and national public-health guidance for real-world precautions. Do not infer individual risk from this toy simulation.

An epidemic curve displays cases by time, often by symptom onset. The shape can help investigators consider outbreak patterns and timing, but it does not prove a transmission route or identify the source by itself.

Observed cases can be fewer than actual infections because of testing access, care-seeking, case definitions and reporting delays. The simulated curve has none of these surveillance complications.

This teaching model simplifies mixing, immunity, infectiousness, interventions and time. It does not include age-specific susceptibility, realistic households, travel, healthcare pathways, pathogen evolution, reinfection, waning immunity, diagnostic delays or a calibrated statistical model.

Its purpose is to build intuition and prompt questions—not to forecast outbreaks, compare real diseases quantitatively, or guide treatment or public-health operations.