1. In groups of 2-3 people, choose a key term related to communicable diseases (e.g., disease, epidemic, endemic, pandemic, communicable, non-communicable, case, prevention, control)

2. Create a post with the term as your subject and provide a clear, accurate definition with an example

3. Review other students’ definitions and leave constructive feedback in the comments

4. Respond to feedback on your own definition to clarify or improve it

Remember: Aim for clear, concise definitions that demonstrate your understanding of the concepts.

It could be direct or indirect

Direct mode of transmission: is when an infectious agent is passed straight from one person to the other without involving a medium e.g sexual transmission ,airborne. vertical etc.

Indirect mode of transmission: this involves transmission through a medium Eg vector-borne transmission, transmission through contaminated food or water etc

Subject: Communicable Disease
Definition: A communicable disease is an infection caused by microorganisms—such as bacteria, viruses, or parasites—that can pass from one person, animal, or surface to another
Example: The flu is a communicable disease that can be transmitted through droplets released when an infected person coughs or sneezes.

example: Smallpox

Causes:

- through direct and prolonged contact(face to face)

-inhalation through airborne droplets

-contaminated items

-indirect contacts through items such as clothing, bedding and towels contaminated through fluids from infected sore

Smallpox is highly infectious, and sometimes fatal disease caused by the variola virus.

Symptoms including : rising temperature(fever), backache, headache and fatigue. Rash in mouth and later red spots and fluid. Changes in skin colour and pigmentation.

Prevention:

- vaccines such as the Jynneos (MVA-BN)

-thorough hygiene

-isolation

-infection control in healthcare settings such as PPE

-stringent disinfection (spraying and cleaning surfaces)

Key intervention may also be education including hygiene education of one’s self and environment.

Mena Oye

Eluyemi

Nailah

Diseases can be transmitted through various modes:

• Direct Contact: Most commonly through skin-to-skin contact, e.g., HIV

• Indirect Contact: Most commonly through contact with a contaminated surface or vector, e.g., Malaria

Is an epidermic of an infectious disease that has sudden increase in cases and spread across a large region, for instance multiple continent or worldwide, affecting a substantial portion of the human population, example are COVID 19,Swine flu, and spanish flu etc.

MODE OF TRANSMISSION

Transmission occurs through direct contact(touching, kissing, sex),indirect contact(surfaces, objects, vectors).

PREVENTION

Routine vaccination

creation of awareness

Health education

Isolation and quarantine

Safe sextual practices

Agent Factors:

Aedes Aegypti and Aedes Albopictus (RNA Virus)

Host Agents:

Humans are the primary host for this dengue fever.

Environmental factors:

Stagnant water

Most prevalent in tropical regions

Poor waste management and water storage practices increase mosquito habitats.

Reservoirs:

1.Humans

2.Mosquitoes

Mode of transmission:

1. RNA virus replicates in mosquitoes

2. Mosquito bites

routes of entry:

1. Through skin by mosquito bite

2. Contaminated needles of the infected host

   
   

   Stages of infection

   1.period of incubation 3-14 days

   2. Febrile phase: 3-7 days

   3. critical phase : 1-2 days

   4. recovery phase: 3-5 days

      
      

      Epidemiologic Factors

      
      

      Distribution: South Asia and Tropical regions

      Not age specific

      Peaks during rainy season

      Risk factors: 1. presence of stagnant water and poor vector control

Action plan for infected population

1. Adequate medication and nutritional supplies

2. isolation

3. Education

Action Plan for non infected population:

1. Water treatment and drainage and cover open water sources

2. Avoid going to Tropical areas

3. Wear long sleeved clothing

4. Mosquito repellents and mosquito nets

5. Health Campaigns

HOST-:

The human.

THE CAUSATIVE AGENT-:

Morbillivirus.

ENVIRONMENTAL FACTORS-:

High population density.

Poor ventilation/overventilation.

Seasonal/Climate variations(Temperate and tropical climate).

Migration and travel.

Poor health infrastructure.

Malnutrition and poverty.

Host

Malaria is transmitted or spread from female anopheles mosquito to humans. These two are the major hosts.

Agent

The causative agent for malaria is a protozoan parasite called Plasmodium falciparum and Plasmodium vivax.

Environment

-Stagnant water like ponds, lakes, streams etc.

-Warm environment with high humidity.

-Poor Sanitation and drainages. E.g Poor waste management and unkept environment.

Activity 3

Mode of transmission: bite of an infected female anopheles mosquito (vector-borne)

Routes of entry : through the skin via a mosquito bite (injection of sporozoites)

Routes of exit:

From infected persons blood-gametoyctes taken up by another mosquito during a blood meal.

Types of transmission:

Vector borne (main route)

Congenital (rare)- mother to fetus

Blood transfusion blood/ needle sharing (rare)

Stages of infection:

Sporozoite stage - injected into human bloodstream - liver

Liver stage - parasites multiply

Erythrocytic stage - merozoites infected red blood cells - symptoms

Gametocyte stage - sexual forms taken up by mosquito - continues cycle

Activity 6

Action plan:

Preventative measures such as clothing- skin covering clothing but mindful of layers due to hot climates.

Advocating for clean environments, increase and reinforcement of antibacterial solutions that are accessible in public spaces and private.

Health improvement and education targeting understanding and knowledge of the process of cleanliness and hygiene.

Insect repellent.

Sleep measures and safety- using mosquito nets and include these on windows and doors.

Vaccinations for malaria

Antenatal measures for extra care including checkups and screening. Encouragement of education and consumation of vitamins to aid the immune system.

Tetanus vaccine for mothers and baby protection.

Encourage iron and folic acid vitamins to prevent anaemia.

Community engagement creating workshops that are fun and exciting for people to unite in understanding and bettering and or maintaining general health

clinical symptoms include coughing, weight loss, fever, night sweat etc.

AGENT: Mycobacterium tuberculosis

HOST: Natural host for M.Tuberculosis is humans affecting all age groups, sexes, although there are preferred genetic susceptibility factors, weakened immune systems also make individuals susceptible to infections.

ENVIRONMENT: Crowded places, poor housing and ventilation, poverty and malnutrition, and high moisture areas.

The Host - Human beings (They specifically multiply in the intestine).

Secondary Host- They are usually in an aquatic environment which serves as a reservoir.

Environmental Factors - Poor sanitation, Warm temperature, Humidity, Limited Access to healthcare, Flooding and Heavy rainfall

Agent- Vibrio Cholerae

Factors That influence transmission

1. Individual hygiene

2. Sick building Syndrome

3. Poor sewage system

   Host Factors that influence transmission

   1. Immunity

   2. Nutrition status

   3. Gastric Acidity

   4. Hygiene Practices

   5. Age and Health status

   6. Socioeconomic and Living conditions

Mode of Transmission - Fecal, oral

Routes of entry - oral

routes of exit- fecal-oral route

Type of transmission- communicable through fecal-oral route

Stages of infection-

Stage 1- Evacuation - Intense stomach cramps, Profuse stooling and vomiting

Stage 2- Collapse - Dehydration, Electrolyte imbalance (Inability to urinate), severe complications

Stage 3 - Recovery- Blood pressure and Body temperature rises and patients begin to urinate again

Action Plan

1. Prevention and preparedness (Improve Wash, Administer Vaccines, Strengthened surveillance)

2. Outbreak response (Rehydration, Zinc supplements, Antibiotics)

3. Long term strategies ( Sustainable Wash solutions, Data analysis)

Agent: Bodily fluids of infected individuals or animals

Environmental factors:

• Tropical Rainforests

• Human factors such as hunting

• Inadequate healthcare infrastructure

HOST: Humans

AGENT: biologic (virus, blood contact, bodily fluids)

ENVIRONMENTAL FACTORS: overcrowding, poverty, lifestyle.

STAGE OF EXPOSURE/MODE OF TRANSMISSION: unprotected sex, sharing sharp object, multiple sexual partners, mother to child, blood transfusion, breastfeeding.

STAGES OF INFECTION:

(i) acute stage: multiplication of virus 2-6 weeks after exposure. Flu like symptoms such as fever, sore throat, body ache, rashes, swollen lymph-nodes, night sweats are experienced at this stage

(ii) latent period: virus remains active and transmissible but slows down on multiplication. this takes 6-10 years and can develop to AIDS without treatment and be asymptomatic due to low viral load

(iii) symptomatic stage: Immune system is now weakened and symptoms fully develop. This includes weight loss, fever, sore throat, body ache, rashes, swollen lymph-nodes, night sweats

STAGE OF OUTCOME: AIDS. Severe immune suppression, life threatening infections, cancers.

If Antiretroviral Therapy begins early, the disease may not progress to AIDS

ACTION PLAN

(i) Prevent transmission through education, safe practices and preventing mother to child transmission

(ii) Promote early testing and Post Exposure Prophylaxis (PEP) for rape victims and people that have had sexual contact with known HIV carriers. The ideal time for PEP administration is 2-72 hours after exposure.

(iii) Distribution of free condoms and Anti Retroviral Therapy (ART)

(iv) Support people living with HIV emotionally, socially and nutritionally.

Tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis, which spreads through airborne droplets when an infected person coughs or sneezes. The agent factors that influence transmission include the bacterium’s ability to survive in the air for long periods and its very low infectious dose, meaning only a few organisms can cause infection. Host factors such as weakened immunity (from HIV, diabetes, or malnutrition), young or old age, and poor adherence to treatment increase susceptibility and prolong infectiousness. Environmental factors like overcrowding, poor ventilation, inadequate sunlight, poverty, and limited access to healthcare promote the spread of TB by increasing close contact and reducing opportunities for early diagnosis and treatment. Together, these host, agent, and environmental factors interact to determine how easily tuberculosis is transmitted within a community.

Host : Human

·       Demographic: Age (young adults and elderly more susceptible), sex (slightly higher in males).

·       Biological:

o   Immunosuppression (e.g., HIV infection, diabetes, malnutrition).

o   Genetic susceptibility (certain HLA types).

·       Behavioral/Social:

o   Poor adherence to TB treatment (incomplete therapy promotes resistance).

o   Substance use (alcohol, smoking, drug use).

o   Low socioeconomic status (crowding, poor nutrition).

Agent : Mycobacterium Tuberculosis

Factors

· Infectious dose: Very small—only a few bacilli can cause infection.

· Survival: Can survive for hours in airborne droplet nuclei under suitable conditions.

· Resistance: Resistant to drying but killed by sunlight and disinfectants.

· Pathogenicity: Causes latent and active TB; only active pulmonary TB cases are infectious.

3. Environmental Factors

• Physical environment:

  • Poor ventilation and overcrowded living conditions (facilitate airborne spread).

  • Inadequate sunlight (MTB is killed by UV light).

• Social environment:

  • Poverty, homelessness, and incarceration.

  • Limited access to healthcare services and TB screening.

  • Migration from high-TB-prevalence areas.

Mode of transmission: air borne (droplets)

Route of entry: nose and mouth

Route of exit: coughing, sneezing, Talking.

Type of Transmission: Direct and indirect.

Stage of infection: Exposure, infection/incubation, clinical manifestation, outcome.

Human.

VECTOR-:

Measles Virus(genus Morbillivirus)

MODE OF TRANSMISSION-:

Airborne transmission

Droplet transmission

Indirect transmission

ROUTES OF ENTRY:

1. Respiratory surfaces

2. Eyes

3. Skin

4. Skin(Epithelial cells)

Route of Exit for Measles:

1. Respiratory tract

2. Nasopharyngeal tract

Mode of Measles Transmission

1. Airbone transmission

2. Droplet transmission

3. Direct contact transmission

4. Indirect contact transmission

Stages of Measles transmission

1. Incubation period: 7-15 days

2. prodromal period: 2-4 days

3. Exathem(Rash): 5-6 days

4. Recovery: Days - weeks.

Type: Bacterium — acid-fast, aerobic, non-spore-forming, slow-growing rod

Major public health concern: Leading cause of death from a single infectious agent globally (esp. in low–middle income countries)

1. Reservoirs

• Primary reservoir: Humans

o People with active pulmonary TB are the main source of infection.

o M. tuberculosis is rarely found in animals (except for M. bovis in cattle — a related species).

• Latent carriers: Humans with latent TB infection (LTBI) act as long-term reservoirs — bacteria remain dormant but viable for years.

• Environmental reservoirs: None significant. The bacterium survives for a time in sputum or dust but doesn’t multiply outside a host.

2. Vectors

• No biological or mechanical vectors.

o TB is not vector-borne. Transmission is human-to-human.

o No insects or animals are involved in the spread of M. tuberculosis.

3. Modes of Transmission

• Airborne transmission (primary mode):

o Inhalation of aerosolized droplet nuclei (<5 μm) containing M. tuberculosis expelled when an infectious person:

 Coughs

 Sneezes

 Speaks

 Sings

o Droplet nuclei can remain suspended in air for hours and travel long distances in poorly ventilated spaces.

• Rare modes:

o Ingestion: Unpasteurized milk containing Mycobacterium bovis (causes zoonotic TB).

o Direct inoculation: Very rare (e.g., lab accidents).

4. Routes of Entry

• Respiratory tract:

o Inhalation of airborne droplet nuclei containing M. tuberculosis bacilli.

o Bacilli reach the alveoli of the lungs and begin infection.

• (Rare) Digestive tract entry via M. bovis in contaminated milk (GI or oropharyngeal TB).

5. Routes of Exit

• Respiratory tract:

o Bacilli exit mainly through respiratory secretions (sputum, droplets) of a person with active pulmonary or laryngeal TB.

o When the person coughs, sneezes, or talks, tiny droplet nuclei containing bacilli are expelled.

• (Less common) Other infected sites can release organisms during invasive procedures (e.g., draining abscesses).

6. Types of Transmission

Type Description Applies to TB? Notes

Direct transmission From infectious person via expelled aerosols Yes Main route — person-to-person

Indirect transmission (fomite, vector, etc.) Through contaminated objects or vectors No MTB is not efficiently spread by fomites

Airborne transmission Via inhalation of droplet nuclei Yes Major mode

Horizontal transmission Between individuals of same generation Yes Primary TB transmission

Vertical transmission Mother → fetus (in utero or perinatal) Rare Possible but uncommon

Zoonotic transmission From animals (esp. M. bovis) Rare Occurs through ingestion of unpasteurized milk

Nosocomial (healthcare-associated) Within hospitals/clinics Yes Risk in poorly ventilated or overcrowded settings

7. Summary Table

Feature Tuberculosis (M. tuberculosis)

Reservoir Humans (main), rarely cattle (M. bovis)

Vector None

Primary mode of transmission Airborne (inhalation of droplet nuclei)

Routes of entry Respiratory tract (lungs)

Routes of exit Respiratory secretions (coughing, sneezing, talking)

Types of transmission Direct airborne, horizontal, occasionally nosocomial, rarely zoonotic or vertical

Period of communicability As long as viable bacilli are present in sputum (untreated active pulmonary TB)

Non-communicable forms Latent TB infection (not infectious)

8. Control and Prevention

• Early detection and treatment: Rapid diagnosis & completion of full drug regimen (DOTS strategy).

• Infection control:

o Ventilation and air filtration in healthcare and congregate settings.

o Respiratory protection (N95 masks for healthcare workers).

o Isolation of infectious patients.

• Vaccination: BCG vaccine (effective mainly in children).

• Pasteurization: Prevents M. bovis transmission via milk.

The virus can be asymptomatically transmitted even if the infected person has no visible symptoms.

The transmission of human papillomavirus (HPV) is influenced by factors within the epidemiologic triad:

the agent (the virus), the host (the infected person and their contacts), and the environment. 

Agent factors (the virus)

• Type of HPV: There are over 200 different types of HPV. Some are considered "low-risk" (e.g., HPV 6 and 11) and typically cause benign growths like genital warts, while "high-risk" types (e.g., HPV 16 and 18) can cause cancer. High-risk types may have higher transmissibility or a greater potential for persistent infection.

• Viral load: The amount of virus present in a lesion or shedding from a person can influence the likelihood of transmission.

• Communicability: The period during which an infected person is contagious is presumed to be high and can last for months or years, even when there are no visible symptoms.

• Infectious mechanism: HPV infects the epithelial layer of skin and mucous membranes and is released as infected cells are shed, requiring direct skin-to-skin contact to enter a new host through microscopic breaks in the skin. 

Host factors (the person)

• Sexual behavior: This is a primary risk factor for genital HPV transmission. Factors that increase risk include:

  • Number of sexual partners

  • Number of sexual partners of one's own partners

  • Age at the start of sexual activity, as young adults have higher rates of infection.

• Immune status: A person's immune system is crucial for clearing an HPV infection. Immunosuppression, whether due to HIV/AIDS, organ transplantation, or other conditions, increases the risk of both acquiring HPV and developing a persistent infection that can progress to cancer.

• Co-infections: The presence of other sexually transmitted infections (STIs) may affect the transmission or persistence of HPV, potentially through influencing the local mucosal environment.

• Age and gender: Common skin warts are more prevalent in children, while genital warts are most common in adolescents and young adults. Women generally have higher reported rates of genital HPV than men.

• Behavioral factors: Smoking is a known cofactor that can increase the risk of persistent HPV infection and cancer. 

Environmental factors

• Sexual norms and practices: Cultural and social norms influence sexual behaviors, including the number of partners and age of sexual initiation, which directly affects HPV transmission rates.

• Socioeconomic status (SES): Lower SES can be associated with behaviors that increase HPV transmission risk, including earlier or riskier sexual behavior. It also influences access to preventative measures like vaccines and screening.

• Healthcare access: Availability of preventative measures, such as HPV vaccination programs, and screening services like Pap smears for cervical cancer, can significantly lower infection rates and the risk of cancer.

• Contaminated objects (fomites): While less common for genital types, some HPV strains that cause skin warts can be spread via inanimate objects, especially in damp environments like public showers. Some documented cases of hospital transmission via contaminated equipment also exist. 

  The timeline for HPV progression varies significantly based on the viral type, individual immune response, and other risk factors. The natural history can range from a rapid, asymptomatic infection that clears on its own to a decades-long process that results in cancer

  
  

  1. Acute infection

  • Timeframe: Within months of exposure.

  • What happens: Following intimate skin-to-skin contact, the virus infects the basal epithelial cells. Most people are asymptomatic and will not realize they are infected. The body's immune system typically mounts a response to clear the virus.

  • Outcome: For most people (around 90%), the immune system clears the infection within one to two years. 

  2. Viral latency or persistence

  • Timeframe: Can occur after the initial acute phase, lasting from months to years.

  • What happens: When the immune system fails to clear the infection, the virus can enter a latent stage. It remains present in low copy numbers within the epithelial cells and may go undetected by standard tests.

  • Outcome: Latent infections can be reactivated by factors such as age and immunosuppression. In a minority of cases, a persistent, detectable infection develops. 

  3. Precancerous lesions (dysplasia)

  • Timeframe: Often takes 5 to 10 years after initial infection for high-risk HPV types.

  • What happens: A small fraction of persistent high-risk HPV infections lead to cellular changes called dysplasia, also known as cervical intraepithelial neoplasia (CIN).

    • Low-grade lesions (CIN 1): Often resolve spontaneously. Around half regress to normal or a lower-grade abnormality within six months.

    • High-grade lesions (CIN 2/3): The cells have more advanced abnormal growth. These are more likely to progress if left untreated, especially in cases of persistent HPV-16 or HPV-18 infection.

  • Outcome: High-grade lesions can be detected and removed through screening tests like Pap smears, preventing them from developing into cancer. 

  4. Invasive cancer

  • Timeframe: Typically takes 15 to 20 years for cervical cancer to develop from the initial HPV infection. For people with weakened immune systems, this timeline can be much shorter, potentially 5 to 10 years.

  • What happens: If high-grade precancerous lesions are left untreated, they can eventually develop into invasive cancer, where malignant cells spread beyond the original layer of tissue.

  • Outcome: The slow progression provides a wide window for effective cancer prevention and early detection through regular screening. 

Vaccine accesibility, achieve high vaccination coverage and cold chain coverage.

2.Surveillance and early detection:-

Case - based surveilance, laboratory confirmation, outbreak response team and data monitoring

3.public awareness and education:

Community awareness, school programs, combact vaccine hesistancy

4.Infection control measures:

Isolation, hospital infection control, contact tracking

5.Policy and resource mobilization.

6.Monitoring and evaluation.

1) EDUCATION AND HEALTH AWARENESS: It is important to educate individuals on the lifestyle modifications to implement to reduce the spread and incidence of TB.

2) GOOD HEALTHCARE SEEKING AND ADHERENCE BEHAVIOURS:

The importance of seeking adequate health care when symptoms develop and adhering and compliance to the treatment regimen strictly as the medications for TB are readily available and free.

3)HEALTHCARE CAMPAIGNS: The use of campaign programs to educate the masses on TB, mode of transmission, signs and symptoms.

4) APPROPRIATE AND AVAILABLE TESTING FACILITIES, This helps in the early detection of cases of TB to limit the spread of TB cases.

5) VACCINATION: Development and distribution of vaccines to the at risk populations.

1. Surveillance & Reporting

   • Mandatory TB reporting and case tracking.

   • Identify high-risk areas and populations.

2. Transmission Control

   • Isolate active cases in healthcare settings.

   • Promote masks, ventilation, and hygiene in the community.

3. Screening & Early Detection

   • Test high-risk groups (contacts, immunocompromised, healthcare workers).

   • Use TST, IGRA, chest X-ray, and microbiological tests.

4. Prevention of Progression

   • Treat latent TB in high-risk individuals.

   • Monitor adherence to therapy.

5. Treatment & Cure

   • Provide DOT with first-line drugs; manage drug-resistant TB.

   • Support patients with nutrition, counseling, and financial help.

6. Community Engagement

   • Raise awareness about TB symptoms and prevention.

   • Reduce stigma to encourage early care-seeking.

7. Health System Strengthening

   • Ensure drug supply, integrate TB services with other health programs.

   • Implement national guidelines aligned with WHO recommendations.

8. Monitoring & Evaluation

   • Track TB incidence, treatment success, and latent TB therapy completion.

   • Conduct research to improve strategies.