unit 3.1.1: communicable & infectious diseases

**Communicable** diseases

* **contagious** disease
* transmitted **from one person to another** through a variety of ways that include**:**
* contact with blood and bodily fluids
* breathing in an airborne virus
* or by being bitten by an insect (vector)

**Infectious** Diseases

* caused by a **pathogen**
* disorders caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi that can be spread directly or indirectly (vector-borne) from one individual to another

pathogen

any microorganism that causes a disease

COVID-19

**Infectious** **Diseases:**

* viral disease


* SARS-CoV-2

Malaria

**Infectious** **Diseases:**

* *Plasmodium spp.*
* parasitic disease

Tuberculosis

**Infectious** **Diseases:**

* lung infection
* *Mycobacterium tuberculosis*

Athlete’s Foot

**Infectious** **Diseases:**

* caused by fungi

No

Are all infectious diseases communicable?

Tetanus

**Are all infectious diseases communicable?**

* bacterial infection caused by *Clostridium tetani*
* it cannot be transmitted easily to another person

15 million

___ of 57 million annual deaths worldwide are the result of infectious disease

Infectiology

* study of infectious diseases
* **medical specialty** dealing with the diagnosis and treatment of complex infections

infectious disease specialist's practice

consists of managing **nosocomial** (__healthcare-acquired__) infections or **community-acquired** infections and is historically associated with **travel medicine and tropical medicine.**

**community-acquired** infections

**infectious disease specialist's practice:**

while living in a **community**, you got the infection

**nosocomial** infections

* preventable

**infectious disease specialist's practice:**

infections acquired in a **healthcare facility**

* acquired by a **patient**

**laboratory** infections

**infectious disease specialist's practice:**

infections acquired in a **laboratory**

* acquired by a **worker** - part of __occupational health__

Tropical medicine

interdisciplinary branch of medicine that deals with health issues that occur uniquely, are more widespread, or are more difficult to control in **tropical and subtropical regions**

endemic

**Tropical medicine:**

Most infections they deal with are ___ to the tropics

**18 lesser known neglected tropical diseases**

* Chagas
* Rabies
* Dengue

**Tropical medicine:**

Physicians in this field must be knowledgeable in the ___

Ignaz Semmelweis

**Historical Landmarks:**

* father of hand washing
* childbed fever
* suffered from depression and brought to an asylum

Higher - **Physicians & Medical Students**

**Historical Landmarks:** *Ignaz Semmelweis -* __*Maternal Mortality Rate*__

First clinic

Lower - **Midwives**

**Historical Landmarks:** *Ignaz Semmelweis -* __*Maternal Mortality Rate*__

Second clinic

Edward Jenner

**Historical Landmarks:**

* **vaccinations**
* used __cowpox__ to create a **vaccine for** __**smallpox**__
* milkmaids were less likely to get the virus

Dr. Henderson

**Historical Landmarks:**

* led the **eradication program against smallpox**
* last disease was detected in Africa in 1978
* formally declared eradicated in 1981

John Snow

**Historical Landmarks:**

* cholera & tracing source of infection
* spot maps
* first to use epidemological tools for the control of a disease
* **father of epidemology**

Robert Koch

**Historical Landmarks:**

* first to isolate bacteria
* Postulates

organisms suffering from disease

**Historical Landmarks:** *Robert Koch*


1. Microorganism must be found in ___

pure culture

**Historical Landmarks:** *Robert Koch*


2. Collected microorganism must be isolated in ___

healthy organism

**Historical Landmarks:** *Robert Koch*


3. Cultured microorganism should be given to a ___

identical

**Historical Landmarks:** *Robert Koch*


4. Microorganism must be reisolated from inoculated experimental host and should be ___ to original agent

Germ theory of disease

**Historical Landmarks:** *Robert Koch*

diseases are caused by a single bacterium

Agent

**The Epidemiologic Triad:**

* referred to an **infectious microorganism** or pathogen: a virus, bacterium, parasite, or other microbe
* not necessarily infectious
* concept of necessary and sufficient causes

Host

**The Epidemiologic Triad:**

* refers to the **human** who can get the disease

Risk factors

**The Epidemiologic Triad:** *Host*

* A variety of factors **intrinsic** to the host can influence an individual’s exposure, susceptibility, or response to a causative agent

behaviors and physiologic susceptibility

**The Epidemiologic Triad:** *Host*

* Opportunities for exposure are often influenced by ___

Environment

**The Epidemiologic Triad:**

* refers to **extrinsic** factors that affect the agent and the opportunity for exposure
* physical factors, biologic factors, and socioeconomic factors

Chain of Infection

* refers to the **spread of infection** (or agent) from a source to a susceptible host
* useful **framework** in the design of __prevention and control measures__
* specific strategies can be aimed at various points along the chain of infection

Reservoir

**Chain of Infection:**

where the agent lives prior to transmission

Mode of Transmission

**Chain of Infection:**

process of how the infection is transmitted

Agent

**Chain of Infection:**

germs

Reservoir

**Chain of Infection:**

where germs live

Portal of Exit

**Chain of Infection:**

how germs get out

Mode of Transmission

**Chain of Infection:**

germs get around

Portal of Entry

**Chain of Infection:**

how germs get in

Susceptible Host

**Chain of Infection:**

next sick person

Prevention

* **Strategies or actions** aimed at __eradicating, eliminating or minimizing the impact of disease__ and disability, or if none of these are feasible , __retarding the progress of disease and disability__
* Reduction in the **risk and severity of a disease** at the **individual** level

Control

* **Ongoing operations** at reducing the:
* Incidence of Disease
* Duration of disease
* Effects of the disease
* Burden to community
* Reduction in the **frequency and severity of a disease** at the **community** level

rapid, accurate identification of organisms

**How to Break the Chain of Infection?**

Infectious Agent

* environmental sanitation
* employee health
* disinfection sterilization

**How to Break the Chain of Infection?**

Reservoir

* PPE
* hand washing
* trash & waste disposal
* control of excretions & secretions

**How to Break the Chain of Infection?**

Portal of Entry

* isolation
* food handling
* air flow control
* sterilization
* hand washing

**How to Break the Chain of Infection?**

Mode of Transmission

* wound care
* catheter care
* aseptic technique

**How to Break the Chain of Infection?**

Portal of Exit

* treatment of underlying disease
* recognition of high risk clients

**How to Break the Chain of Infection?**

Susceptible Host

SARS-COVID 2

**Chain of Infection:** *COVID-19*

Agent

Bats, Infected individuals

**Chain of Infection:** *COVID-19*

Reservoir

Mucus, biological fluids

**Chain of Infection:** *COVID-19*

Portal of Exit

Airborne, direct contact

**Chain of Infection:** *COVID-19*

Mode of Transmission

Inhalation of contaminated air

**Chain of Infection:** *COVID-19*

Portal of Entry

Comorbidities, elders, children

**Chain of Infection:** *COVID-19*

Susceptible host

Virus

**Chain of Infection:** *Rabies*

Agent

Domesticated or wild animals

**Chain of Infection:** *Rabies*

Reservoir

Saliva

**Chain of Infection:** *Rabies*

Portal of Exit

Licking

**Chain of Infection:** *Rabies*

Mode of Transmission

Puncture or open wound

**Chain of Infection:** *Rabies*

Portal of Entry

Non-vaccinated people

* usually children

**Chain of Infection:** *Rabies*

Susceptible host

96%

**Species Affected by Rabies:**

positives from canines

72%

**Species Affected by Rabies:**

rabies cases were owned pets

88%

**Species Affected by Rabies:**

rabies cases were free roaming

smallpox, measles and polio

**Chain of Infection:**

have no non-human reservoir

smallpox

**Chain of Infection:** *Smallpox, Measles, & Polio*

concept of vaccination originated with ___

**molecular sequence** of the virus is publicly known

**Chain of Infection:** *Smallpox Eradication*

One concern is that the ___, meaning that someone could synthesize it in a laboratory and loose it on the world

Dr. Henderson

**Chain of Infection:** *Smallpox Eradication*

*“Let’s destroy the virus and be done with it... We would be better off spending our money in better ways.”*

Polio

**Chain of Infection:**

contagious viral illness in its most severe form that causes **paralysis, difficulty breathing, and death**

2000

* it was not met

**Chain of Infection:** *Polio*

In 1988, at a time when **350,000 children were being paralyzed** each year, WHO set a goal of eradicating polio by the year ___

99% worldwide

**Chain of Infection:** *Polio*

by 1999, annual polio cases were reduced by

Nigeria, Pakistan, and Afghanistan

**Chain of Infection:** *Polio*

Only three countries continue to have endemic polio

In humans, found in feces

**Chain of Infection:** *Polio*

Agent

patient treatment

**Chain of Infection:** *Polio*

Agent: How to break the chain?

Areas that have **poor sanitation**

* Fecal-oral route

**Chain of Infection:** *Polio*

Reservoir

* improved public sanitation


* vaccines
* personal hygiene

**Chain of Infection:** *Polio*

Reservoir: How to break the chain?

* Pregnant women
* Children
* Weak immune systems

**Chain of Infection:** *Polio*

Susceptible Hosts

* respiratory secretions
* ingestion
* bathroom

**Chain of Infection:** *Polio*

Portal of Exit

* hand washing
* keep area clean & disinfected

**Chain of Infection:** *Polio*

Portal of Exit: How to break the chain?

* contaminated water
* direct contact with infected person

**Chain of Infection:** *Polio*

Mode of transmission

check if food is contaminated

**Chain of Infection:** *Polio*

Mode of transmission: How to break the chain?

* eyes
* mouth
* nose

**Chain of Infection:** *Polio*

Portal of Entry

Research

**Chain of Infection:** *Polio*

* 2%
* to **facilitate eradication**

Vaccines

**Chain of Infection:** *Polio*

3%

Surveillance

**Chain of Infection:** *Polio*

* 11%
* disease detection

Social Mobilization

**Chain of Infection:** *Polio*

* 19%
* raise **awareness** of vaccination campaigns & benefits of immunization

Technical Assistance

**Chain of Infection:** *Polio*

* 20%
* **salaries** for health professionals

Operational Support

**Chain of Infection:** *Polio*

* 45%
* **stipends for community based vaccinators** that administer house-to-house visits

* **400 to 500 deaths** a year in the United States
* 4000 cases of **chronic disability** from measles encephalitis

**Chain of Infection:** *Measles*

Before a vaccine was available, almost all children contracted measles, causing ___

1963

**Chain of Infection:** *Measles*

vaccine became available in ___

vaccinated as babies

**Chain of Infection:** *Measles*

outbreaks of measles began to occur among high school and college students who had been ___

Rubeola virus

**Chain of Infection:** *Measles*

Agent

* respiratory tract
* nasal passages
* throats

**Chain of Infection:** *Measles*

Reservoir

* **air currents**: airborne droplets
* direct secretion

**Chain of Infection:** *Measles*

Mode of Transmission

inhalation

**Chain of Infection:** *Measles*

Portal of Entry

secretion

**Chain of Infection:** *Measles*

Portal of Exit

* non-vaccinated
* close proximity to infected

**Chain of Infection:** *Measles*

Susceptible Host