Epidemiology

human health

state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity

Improved health leads to…

• gains in economic, social, & educational aspects of society

• successful, functional society

What is the cycle of public health?

→ assess health of a population → determine causes of any health problems → implement & evaluate solution →

epidemiology

basic science of public health;

branch of medical science that studies factors which determine presence and absence of diseases and disorders

What are 3 aspects of the Ascaris life cycle?

• direct

• no IH

• no amplification

draw the Ascaris model, and label each part

A = adults

r = per capita reproductive rate

E = eggs

β = per capita transmission rate

µ1 = per capita death rate for A

µ2 = per capita death rate for E

How do you get the net reproductive rate (# of eggs) from the Ascaris model?

multiply r x A

How do you get the # of new adults from the Ascaris model?

multiply # of eggs by β
rA x β

How do you get the total # of adults from the Ascaris model?

multiply # of eggs by β
rA x β
then add the original # of adults
(rA x β) + A

What factors affect transmission rate?

• number of eggs

• number of hosts

• host behavior

• parasite survival in host

How do you get the # of adult worms removed from the population from the Ascaris model?

multiply A x µ1

How do you get the # of eggs removed from the population from the Ascaris model?

multiple E x µ2

Which components of the Ascaris model involve parasite reproduction & transmission?

rA and β

Which components of the Ascaris model involve parasite elimination?

Aµ1 and Eµ2

If reproduction & transmission > elimination, then…

parasite will survive in host population

What is the best method of control of Ascaris?

chemotherapy and education

R₀

basic reproductive ratio;

average # of secondary cases a typical single infected case will cause in a population with no immunity to the disease and in absence of interventions to control infection

Threshold level of parasite survival occurs at R₀ = __

1

To eradicate a parasite species, R₀ < __

1

What is the R₀ of smallpox without human intervention?

2

What is the R₀ of Ascaris without human intervention?

5

What is the R₀ of measles without human intervention?

8

What is the R₀ of malaria without human intervention?

50

eradication

• no longer exists anywhere in the world

• seldom realistic

elimination

• localized eradication

• no longer exists in a specific geographical region

Smallpox natural exposure →

long-lasting immunity

What were the 4 reasons for the success of smallpox eradication?

1. vaccine

2. no animal reservoir

3. government cooperation

4. $$$

What was the most important reason for the success of smallpox eradication?

vaccine

What were the features of the smallpox vaccine that made it so successful?

• long-lasting protective immunity

• 1 dose

• easy to administer

• effective delivery & education campaign

• fear of disease → public acceptance

Are there a lot of vaccines available for parasites?

no, very few

What is the only parasite species that may soon be eradicated, and why?

Dracunculus, because of education and control measures, NOT VACCINE

What are 4 reasons why many human parasites have been eliminated from developed countries?

1. increased living standards

2. sanitation

3. improved hygiene

4. improved meat inspection

draw the life cycle of Enterobius vermicularis

What are the steps in the life cycle of Enterobius vermicularis?

1. eggs on perianal folds (butthole)

2. larvae mature inside the eggs within 4-6 hours

3. embryonated eggs are ingested by a human

4. larvae hatch in small intestine

5. adults in lumen of cecum

6. gravid female migrates to perianal region (butthole) at night to lay eggs

What are the two types of infection in Enterobius vermicularis?

1. retroinfection

2. autoinfection

What is retroinfection in Enterobius vermicularis?

eggs hatch in perianal region and L₁ migrates back in

What is autoinfection in Enterobius vermicularis?

host ingests eggs produced by worms in the body

What is the morphology of Enterobius vermicularis eggs?

• flattened side

• coffee bean

What is the morphology of Enterobius vermicularis adults?

• alae (thickened cuticle at the anterior end)

• female → pinworm

• male → curved posterior

What is the pathology of Enterobius vermicularis?

• most asymptomatic

• damage within intestine & around anus → inflammation & bacterial infection

• sleeplessness & irritability

How do you diagnose Enterobius vermicularis?

Scotch tape test

What is the treatment for Enterobius vermicularis?

• Pyrantel

• Albendazole

• Mebendazole

treat EVERYONE in the household

What demographic is most affected by Enterobius vermicularis?

young children

• daycare hygiene

• sleeping → itch → fingers in mouth

• airborne