10. Vector-borne Disease Flashcards
Vector-borne Disease definition
Infections transmitted to humans by the bite of an infected arthropod species (vector)
Vectors
Living organisms that can transmit infectious diseases between humans or from animals to humans.
Mosquitoes: West Nile virus, Malaria, Dengue fever, Zika Virus disease
Ticks: Lyme disease, Rocky Mountain spotted fever • Fleas Plague
Lyme Disease
Maintained in zoonotic cycles involving a variety of wild mammals & birds as reservoirs. E.g. White-footed mouse.
Blacklegged Tick is the most important vector in the transmission of Lyme disease.
Ticks do not fly, hop, or jump. They Questing.
If host animal is infected with B. Burgdoferi, the tick can ingest the pathogen and become infected; if the tick later feeds on a human, transmission can occur (for life)
- Longer the tick is attached, the greater the chance for transmission
- Removal within 24 hours can greatly reduce risk of transmission
Epidemiology Lyme
Lyme disease is the most commonly reported vector-borne illness in the US.
Incidence varies dramatically between geographic regions
- Prevalence of Ixodes ticks & proportion infected
- Opportunity for human exposure to infected ticks
Ratio of apparent to inapparent infection is 1:1
Age distribution is bimodal with peak in children (5-14) and adults (50-59 years);
Transmission peaks in spring/early summer when ticks are most abundant and active
Risk factors – living, working, vacationing in a woodsy, rural environment
Lyme (Clinical Manifestations)
Early (3 – 30 days): Flu-like symptoms, Erythema migrans (EM) rash
Late (weeks – months): Arthritis (60%)
Diagnosis Lyme
Clinical presentation: EM rash is characteristic and history of potential infected tick exposure supports diagnosis
Laboratory testing: 2 step process to test blood for evidence of antibodies against B. burgdoferi
- Step 1: Enzyme immunoassay (EIA) test. If negative then No further testing; if positive, goS to step 2
- Step 2: Immunoblot (Western blot) test. If negative then negative for Lyme disease; if positive then positive for Lyme disease
Lyme Treatment
2 – 4 weeks of oral antibiotics for uncomplicated cases
Patient with cardiac or neurologic symptoms may require IV antibiotics
Patients treated early typically recover quickly and completely
Post-treatment Lyme Disease Syndrome – lingering symptoms of fatigue, pain, & joint or muscle aches following treatment which can last 6 months or longer; exact cause is unknown
Prevention of Lyme Disease
Best method of prevention is to avoid the vector and bites from the vector.
Know where to expect ticks. Blacklegged ticks like moist, humid environments in/near wooded/grassy areas
Apply insect repellent (DEET) to skin & clothing (protection for several hours).
May apply .insecticide (permethrin) on clothing or gear (protection through several washings).
Perform daily tick checks when returning from an area that may have ticks.
Remove attached tick (with fine-tipped tweezers) as soon as it is noticed (risk for Lyme disease low if removed within 24 hours).
Arboviruses
ARthropod-BOrne virus infections
Transmitted by specific species of mosquitoes/ticks that are present in specific ecologic systems
Temperate climates – seasonal in nature / Tropics – year round
Virus must replicate in vector, then travel from stomach to salivary glands before transmission can occur
Extrinsic incubation period
Interval of time that starts when vector ingests a blood meal from a viremic host and ends when the virus appears in the salivary glands of the arthropod (may now transmit to others). Averages 6 – 10 days for most arboviral infections.
Dengue
Most important arthropod-borne viral disease of humans worldwide
In the past 30 years, the frequency of epidemics has increased substantially in most tropical countries in the American region
In the continental U.S., travel associated dengue cases occur, as well as limited outbreaks
Most cases of dengue in U.S. citizens occur as a result of endemic transmission in U.S. territories
Dengue Transmission
To become infected, mosquito must feed during a 5 day period when there are high levels of virus present in an individual’s blood
In 8-12 days, mosquito is able to transmit to another person
Mosquito remains infected for life
Dengue Clinical Information
Symptoms begin 4-7 days after bite and last 3 – 10 days
DHF: more severe form of dengue involving damage to blood vessels leading to bleeding and fluid accumulation
Definitive diagnosis requires laboratory testing via isolation of the virus (PCR) or identification of dengue-specific IgM antibodies (ELIZA)
There is no specific treatment; treatment is supportive and involves pain & fever management and hydration High fever, severe headache, muscle, bone & joint pain, rash
West Nile Virus
Arbovirus spread by mosquitoes that can cause febrile illness and in rare cases, encephalitis (inflammation of brain)
Cases have occurred in the U.S. every year since 1999
West Nile Clinical Information
Highest risk for severe disease: 60 years of age and older & those with chronic medical conditions.
Testing: Typically via detection of West Nile virus specific IgM antibodies (commercially available); Viral culture and PCR can be requested through state labs or CDC.
Treatment: No specific treatment; treatment is supportive with pain & fever management and hydration if necessary
