Exam 2: Vector-Borne Diseases

Lyme Disease, Rabies, Yellow Fever, African Sleeping Sickness, Malaria

What is the most common vector-borne infection?

Lyme Disease

What is the rate at which vector borne infections have increase since the 2000s?

Exponentially

Why have the rates of vector-borne infections increased?

* Increased reporting
* Increased number of vectors
* Increased geographic spread
* Increased travel

Causitive agent of Lyme Disease

*Borrelia burgdorferi*

Characteristics of *Borrelia burgdorferi*

* Spirochete
* Motile (flagellated)
* Gram-negative

What is different about the genome of *Borrelia burgdorferi*?

Linear chromosome

What is a unique characteristics about the plasmids in *Borrelia burgdorferi*?

Carries up 21 plasmids for many different functions

* Infection capabilities
* Infect a large range of hosts
* Drug resistance
* Persistance in the human body

Instead of using iron, what does *Borrelia burgdorferi* use?

Manganese

What are the two other species of *Borrelia* that are most commonly found in Europe and Asia?

* *B. afzelii*
* *B. garinii*

What is the rare species of *Borrelia* that is found in the U.S.?

*B. mayonii*

How was *B. mayonii* identified?

* Normal Lyme Disease tests came back negative or inconclusive
* Had to be isolated and cultured
* Similar type of symptoms (GI, large rash, higher bacterial load)

Where was Lyme Disease first studied?

Old Lyme, Connecticut

What wass the original diagnosis for the patients in Old Lyme, Connecticut?

Contagious rheumatoid arthritis

What were the characteristics of the outbreak in Old Lyme, Connecticut?

* Presented with one-sided, large joint arthritis
* Bulls-eye rash before arthritis

How were all the cases of Lyme Disease in Old Lyme, Connecticut connected?

* Many victims lived on the same street
* All victims lived close to a wooded area

What is the estimated number of documented cases of Lyme Disease per year?

30,000-40,000 cases

Is the actual number of Lyme Disease cases per year predicted to be underestimated or overestimated?

Underestimated

Why do ticks seem to prefer the Northern U.S. to the Southern U.S.?

* White footed mice are good carriers of Lyme Disease to feed off of
* Ticks care for cooler temperatures
* Skinks and lizards form the South are terrible carriers

What are the symptoms of Lyme Disease?

* Fever
* Headache
* Fatigue
* Rash
* Bulls-eye

What are the many other possibilities for symptoms of Lyme Disease?

* Swollen lymph nodes
* Sore throat
* GI symptoms
* Chest pain
* Heart palpitations
* Dizzy

What are two co-infections that can commonly occur with Lyme Disease?

* Babesia
* Protist
* Anaplasma
* Bacteria

What are the 4 steps in a tick’s life cycle?

1. Egg
2. Larve
3. Nymph
4. Adult

What is the most dangerous form of a tick’s life cycle?

Nymph

How long does human infection take for Lyme Disease?

About 36 hours

What is unique about the tick after it attaches to the human host?

The tick has enzymes that will alter the human host’s immune response

Why is the diagnosis of Lyme Diseasse difficult?

* Multitude of symptoms
* Culture from skin biopsies or blood (slow growing)
* Antibody bades tests (can have false positives or false negatives)

What is the treatment for Lyme Disease?

Antibiotics

Why did the previous Lyme Disease vaccine stop production?

* Not effective
* Not enough risk
* Boosters were needed every 1-2 years
* Cost more than the antibiotics
* People started rumors

What is unique about the new possible Lyme Disease vaccine?

* mRNA based
* Attacks the proteins in the ticks

What percentage of people develop Chronic Lyme Disease?

10%

Symptoms of Chronic Lyme Disease

* Fatigue
* Chronic pain
* Arthritis
* Memory problems

Does Chronic Lyme Disease develop before or after the initial Lyme Disease is treated?

After

What are two potential reasons for Chronic Lyme Disease?

* Persistent antigens
* Initial infection triggers an underlying condition in host

Are humans the dead end host for yellow fever?

No

What continent are the majority of yellow fever cases diagnosed in?

Africa

What percentage of yellow fever cases are asymptommatic?

50%

What are the animal reservoirs for sylvatic yellow fever?

Monkeys

Does yellow fever have the ability to affect animal carriers?

Yes

Can humans transmit yellow fever?

Yes

What is the process of sylvatic yellow fever?

Nonhuman primates → Mosquito → Nonhuman primate → Mosquito

What is the process of urban yellow fever?

Mosquito (sylvatic) → Human → Mosquito → Human (savannah) → Mosquito

What is the process of savannah yellow fever?

Nonhuman/human primate → Mosquito → Nonhuman/human primate → Mosquito

Between what two types of transmission events can cause a spillover evevnt?

Sylvatic and urban

What transmission event has a higher epidemic risk, and therefore has higher fatallities?

Urban

Can asymptommatic yellow fever patients contribute to an outbreak?

Yes

What are the mild symptoms of yelllow fever?

* Sudden onset
* Nonspecific
* Flu-like symptoms
* About 30-33% of patients

What are the severe symptoms of yellow fever?

* Jaundice
* Kidney damage
* Multiorgan failure
* Shock

What percentage of yellow fever patients develop severe symptoms?

12-15%

What is the fatality rate of yellow fefver with severe symptoms?

45-50%

What are 5 methods used to diagnose yellow fever?

* Symptoms
* Travel
* Exposure to vector
* Antibodies
* Viral isolation

What is the treatment for yellow fever?

Supportive care

What are the recommended methods to prevent yellow fever?

* Avoid mosquito bites
* Vaccines
* Fractional dosing

What is the problem with the yellow fever vaccines?

Shortages

What type of vaccine is the yellow fever vaccine?

Attenuated virus

* 1-2 doses for lifelong immunity

What is fractional dosing?

Taking one full dose of the yellow fever vaccine and dividing it into five smaller doses

When is fractional dosing used?

When there are limited doses of the yellow fever vaccine

What are the main goals of the Eliminate Yellow Fever Epidemics (EYE) strategy?

* Shut down epidemics
* Prevent spread from one country to another
* Contain outbreaks
* Protect vulnerable populations
* Vaccinate
* Increase vaccine supply
* Improve diagnostic methods
* Surveillence

What are two reasosn that we cannot eridicate yellow fever?

* Asymptommatic carriers are hard to track
* Animals and vectors can carry adn transmit

Why are the EYE strategies not going well?

COVID

What type of transmission has Brazil had over the past century?

Urban

What year did the Brazil yellow fever outbreaks change to the sylvatic cycle?

1940s

What caused the trend change in Brazil for yellow fever cases?

Changes in seasons

How did the outbreak in Brazil start?

Drought

How did yellow fever persist in Brazil?

* Spillover event
* Vaccines were less effective
* Aedes mosquito population decreased
* Huemagogus mosquito population increased

What is the causative agent for rabies?

Rabies virus

How long has rabies been estimated to be in the population for?

Thousands of years

What continent is rabies not found on?

Antartica

Who had the first idea of attenuation?

Louis Pasteur

How did Pasteur create the rabies virus?

* Joseph Meister was bitten by a dog with rabies
* Parents agreed to let Pasteur to use attenuated vaccine on Meister
* Meister survived

What are the characteristics of the rabies virus?

* Rhabdoviridae family
* Bullet shaped
* *Lyssavirus* genus
* Negative stranded ssRNA genome

What is the main risk for human exposure globally?

Dogs

What is the main risk for human exposure in the U.S.?

Wildlife

What is the typical mortality rate of rabies in the U.S.?

1-3 reported death

Why are the U.S. human exposure risks different than the global exposure risks?

Successful dog vaccination programs

* Dogs are not considered to be a reservoir for the virus

What is the primary transmission type for rabies?

Animal to human

* Saliva
* Brain/nervous system tissue

What are 3 ways that animal brain/nervous system tissue can enter humans?

* Open wounds
* Cross mucus membranes
* Ingestion

What are two types of transmission that rabies can be transmitted human to human?

* Organ transplants
* Corneal transplants

Incubation period of rabies is dependent on what factors?

Where you are bitten (number of nerves exposed)

If the rabies virus has reached the nervous system, what does that mean?

Symptoms will appear

What are the initial symptoms of rabies?

* Fever
* Tingling at bite site
* Sore throat

What is the most common form of the neuroinvasive symptoms?

Furious

What are the symptoms for the furious form of neuroinvasive rabies?

* Hyperactive behavior
* Hydrophobia
* Encephalitis

How fast is the progression of furious neuroinvasive rabies?

2-3 weeks

What are the symptoms of paralytic neuroinvasive rabies?

* Gradual paralysis

How long is the progression of paralytic neuroinvasive rabies?

Few months

Why is paralytic neuroinvasive rabies underreported?

Symptoms are similar to a neurodegenerative disease

What are two types of diagnostic methods for rabies in humans?

* Clinical presentation + exposure
* Detection of virus

What are two types of diagnostic methods for rabies in animals?

* Observation


* Brain tissue

What is prophylactic treatment and post-prophylactic treatment for rabies?

* Antibodies
* Vaccine after a few days

Once the rabies symptoms develop, what is the prognosis?

* Near 100% fatality rate
* Supportive care
* Comfort

Is is possible for nonlethal rabies to over occur?

Yes, there are 3 survivors that have been recorded

Causative agent of African Sleeping sickness

*Trypanosoma brucei*

What is the vector for African Sleeping Sickness?

Tsetse fly

What is the scientific name for the causative agent of East African Sleeping Sickness?

*Trypanosoma brucei* subspecies *rhodesiense*

What is the primary reservoir for East African Sleeping Sickness?

Animals

Prevalence of East African Sleeping Sickness?

Few hundred cases in Africa per year

What is the scientific name for the causative agent of West African Sleeping Sickness?

*Trypanosoma brucei* subspecies *gambiense*

What is the primary reservoir for West African Sleeping Sickness?

Humans and animals

Prevalence of West African Sleeping Sickness?

7000-10000 cases in Africa per year

Characteristics of Tsetse flies?

* Live in heavily wooded areas in vegetation
* Bite during the day
* Both males and females can transmit
* Endemic area of tsetse flies = Low numbers of infected flies