MICROBIOLOGY EXAM 3

Features of Neglected Tropical Diseases (NTD)

High prevalence (1 out of 7 people), low morality, chronic, linked to rural poverty, stigmatizing

Definitive Host

Host in which the parasite reaches maturity and undergoes sexual reproduction

Intermediate Host 

Host in which the parasite undergoes asexual reproduction

Incidental Host

Intermediate host that doesn’t allow for parasitic spread

Elimination

Reduction in the number of cases to the point where the transmission has been interrupted

Eradication

Reduction in prevalence of infection where transmission has been interrupted and doesn’t need any public health measures

“Unholy Trinity” aka 3 Most Common STHs

1. Roundworm

2. Hookworm

3. Whipworm

Extremely common for children to be infected with all three

Roundworm Infection

~1 billion infected, 5-14 inches as an adult, located in the small intestine, 3-8 years old are the most affected

Hookworm Infection

600 to 700 million infected, 0.3 to 0.5 inches as an adult, located in small intestine, blood feeding infections

Whipworm Infection

500 to 600 million infected, 1-2 inches as an adult, located in large intestine

Common Effects of Unholy Trinity

Stunting of growth of children, cognitive impairments, malnutrition (protein and vitamin a deficiency, anemia)

Genus of Roundworm Infections

Ascaris lumbricoides

Where do adult roundworms live and mate?

Small Intestine (eggs are passed in the stool)

Definitive Host for Roundworm Infections

Humans

At what stage, is the roundworm parasite infectious?

Embryonic Stage

Where do roundworm eggs hatch into larvae?

Small Intestine

How are humans infected with roundworm?

Eggs are passed through the soil and are in the environment

Female Roundworms

Can produce 200,000 eggs per day and adults can live in the small intestine for up to 1.5 years

Diagnosis of Roundworm Infections

Examination of stool for eggs, chest radiographs, ultrasound and radiology for intestinal obstruction

Treatment of Roundworm Infection

Benzimidazoles (BZA) and routine deworming (2-3 times per year)

How long can eggs of roundworms persist in the soil?

10 years (however, they are starting to show resistance to Benzimidazoles)

How does a human get a Hookworm Infection?

Larval form of the parasite attaches to and enters the host skin through any exposed skin

Where does the Hookworm larvae parasite mature into adults?

Small Intestine

Following a Hookworm infections, what do individuals feel?

Develop itchy condition as the larvae migrates to the lungs (5-8 weeks)

What kind of host are humans with hookworm infections?

Definitive Host

Infection with only 25 adult hookworms can lead to

1mL blood loss per day equaling a child’s daily iron requirement 

Diagnosis of Hookworm Infection

Collect stool specimen, fix specimen in 10% formalin, concentrate specimen, examine by microscope for characteristic hookworm eggs

Treatment of Hookworm Infections

Benzimidazole Drugs

Prevention of Hookworm Infections

Sanitary disposal of human waste, large scale deworming campaigns

How much does it cost to deworm a single person?

0.03 to 0.04 cents per dose

Whipworm Infection Genus

Trichuris Trichiura or Trichocephalus Trichiurus

How long does it take for whipworm eggs to become infectious when deposited in soil?

15-30 Days

After ingestion, where do the eggs hatch and what do they release?

Small Intestine releasing Larvae

Whipworm Symptoms

Dysentery, iron deficiency anemia, finger clubbing (best clinical indicator: swelling of nails)

Where do Whipworm larvae develop into adults?

Large Intestine

Infection

Persistence of an organism in or on the host (colonization of the host)

Infectious Disease

Colonization or invasion of the host resulting in tissue damage

Pathogenicity

Ability for an organism to cause disease

Virulence Factors

Any component of a microorganism that contributes to invasion, evasion/subversion of host defenses, tissue damage

Primary Pathogen

Microorganism/microbe that causes disease even in healthy host (Example: Varicella/Chicken Pox)

Opportunistic Pathogen

Microorganism that normally causes disease only in hosts that are compromised (immunodeficient or body wound/opening) (example: pseudomonas aeruginosa)

2 Host Defense Factors

1. Immune status of an individual

2. Coevolution of hosts and pathogens

What are the most common routes of entry?

Ingestion (Salmonella), Trauma (Stabbed/Shot), Needle Sticks, Bites

5 Steps to Infectious Diseases

1. Adherence

2. Replication

3. Invasion

4. Evasion of Host Defenses

5. Tissue Damage

Adhesins

Surface of microbe that has the ability to attach to the host cell receptor (integrin)

Integrin

Host cell receptor that adhesins bind to

Pili Adhesins

Gram Negative, hair-like on surface of bacteria, facilitate adherence of uropathogens to mucosal surface of bladder

Non-Pili Adhesins

Gram Positive

Bacterial Capsules Adhesins (Key Virulence Factor)

Extracellular polysaccharide matrix that provides adherence to host cells and to other bacteria (biofilms: allows bacteria to colonize), prevents phagocytosis

Composition of Integrins

Glycolipids or Glycoproteins (important for host cell function)

What do Integrins determine?

Host Tropism

Host Tropism 

Susceptibility of a host to infection by a microorganism (which animals can be infected by these organs)

Tissue Tropism

Cells/tissues of a host that support the growth of a microorganism (which tissues can be colonized by the microbe)

Sites of Replication

Extracellular Growth and Intracellular Growth

Extracellular Growth 

Growth outside of host cells

Intracellular Growth

Growth inside of host cells

Facultative Intracellular 

Growth on either mucosal surfaces or within host cells (Example: Salmonella) 

Microorganisms that damage host cells must escape and…

Invade a new host cell (viruses may bud from a host cell or escape via lysis of the host cell)

Listeria (Gram +) and Shigella (Gram -) exploit host cell proteins to…

Propel themselves into adjacent healthy host cells

Genus of Salmonella

Salmonella Enterica

Salmonella

Gram Negative, Rod Shaped, Facultative Anaerobe, Peritrichous Flagella, Facultative Intracellular Pathogen 

Clinically Relevant Salmonella Types 

Typhi (causes typhoid fever), Paratyphi (causes typhoid fever), Typhimurium

Facultative Anaerobe 

Grow using oxygen by aerobic respiration or grow without oxygen by anaerobic/fermentation

Salmonella Prevalence

1 of 4 major causes of diarrheal disease globally (~1 billion illnesses each year, 3 million deaths globally): 60-80% are undiagnosed/sporadic

How long does Salmonella last? How long does it take to onset after ingestion?

Onset occurs 6-72 hours after ingestion and lasts 2-7 days

What are the age groups most at risk for getting Salmonella?

Young, Elderly, and Immunocompromised Individuals

Enteric (Typhoid) Fever

Occurs in low-income countries

How can Salmonella bacteria be passed along?

Food chain all the way from animal feed to restaurants

Is there a vaccine for Salmonella?

No

Reptiles and Amphibians with Salmonella

Reptiles have Salmonella on their skin

Diagnosis of Salmonella

Stool collection and antigen testing, DNA testing, and blood testing

Treatment of Salmonella

Hydration/electrolyte replacement, anti-diarrheals, and antibiotics (only for severe cases)

What can Dissemination also lead to? (Salmonella)

Colonization of the gallbladder and chronic shedding (Typhoid Mary)

Which disease was used in the first bioterrorist attack?

Salmonella

Rajneeshee Cult

Cult wanted to secure political power but realized they couldn’t get enough votes so they contaminated salad bars at restaurants with Salmonella and infected 751 people and caused 45 hospitalizations

What was the 2nd NTD disease that was eradicated?

Guinea Worm Disease

Schistosomiasis Genus

Schistosoma

Intermediate Host of Schistosomiasis

Snails

Definitive Host of Schistosomiasis

Humans

Symptoms of Schistosomiasis

Acute/Early Symptoms: Rash/itchy skin, fever, chills, cough and muscle aches
Chronic Symptoms: Abdominal pain, enlarged liver, blood in stool/urine, difficulty urinating, permanent damage to liver/spleen/intestines/lungs/bladder/kidneys

Eggs shed by adult females become lodged in… (Schistosomiasis)

Intestine or bladder causing inflammation and scarring

What do children develop when they contract Schistosomiasis?

Anemia, malnutrition, learning difficulties (it is not just 1 infectious disease that is keeping poor countries poor, it is multiple)

What do women with Schistosomiasis develop?

“Sandy patches” in the vulva, vagina, cervix and uterus and they are 3-4x more likely to contract HIV

Schistosomiasis Prevalence and Mortality Rate

Very high prevalence (240-600 million cases) with a low mortality rate (200,000 deaths)

Diagnosis of Schistosomiasis

Examine urine and stool samples for eggs, serologic test

Treatment of Schistosomiasis

Praziquantel: 1-2 days (can be used for all species of Schistosomiasis)

London Declaration

Holistic approach to combat Schistosomiasis (Gates Foundation, World Bank, WHO, and governmental/non governmental organization joined)

Schistosomiasis Control Initiative (SCI)

Aids governmental health ministries to implement effect control measures (very cheap for American tax payers)

Genus of Elephantiasis 

Lymphatic Filariasis 

What is Elephantiasis caused by?

Parasitic Nematodes (Roundworms)

3 Species of Elephantiasis 

Wuchereria bancrofti, Brugia malayi, Brugia timori

What is Elephantiasis transmitted by?

Mosquito Bite

What do Chronic Elephantiasis infections result in?

Disfigurement and Permanent Disabilities

Elephantiasis Vectors

1. Culex → Urban/Semi Urban (Daytime)

2. Anopheles → Rural (Nighttime)

3. Aedes → Pacific Islands

The current drugs we have to prevent Elephantiasis only kill

Larval form (if they have adult worms, the drugs we have will not kill them)

How long can Wuchereria Bancrofti live inside of a human host?

8 Years

Acute Adenolymphangitis

Leads to onset of high fever, painful lymph node, lymphatic inflammation, and local edema (usually occurs in adolescence), episodes last 4-7 days with 2-3 recurrences per year

Tropical Pulmonary Eosinophilia (TPE) 

Syndrome of person in their 30s, affecting more men than women (4:1)

Lymphedema

Gradually gets worse and worse, grade 2 and grade 3 are elephantiasis