Vector-Borne Disease
Toxic phase
15% of cases progress to this phase high fever jaundice, bleeding, shock and organ failure with 25-50% mortality
Ratio of inapparent to apparent for lymes
1:1
West Nile Incubation period
2-6 days (range of 2-14)
West nile those at risk for severe disease
60+ years those with chronic medical conditions 10% mortality among those that develop severe disease
West Nile Clinical Information
79% have no symptoms 20% have west nile fever fever headache body aches fatigue 1% have west nile encephalitis high fever severe headaches stiff neck disorientation/confusion stupor or coma tremors convisions partial paralysis
Arboviruses
ARthropod BOrne virus infections virus must replicate in vector, then travel from stomach to salivary glands before transmission can occur important causes of encephalitis and hemorrhagic fever transmitted by specific species of mosquitoes/ticks present in specific ecologic systems dengue, west nile, yellow fever, chikungunya, and others
Diagnosis of Lyme disease
Clinical presentation--EM rash is characteristic and history of potential infected tick exposure supports diagnosis Laboratory testing
Most important vector in transmission of lyme disease
Ixodes scapularis--blacklegged tick complicated life cycle taking 2 years to complete (egg, larvae, immature nymph, mature adult tick) blood meal required for progression to next stage
mosquito borne encephalitis viruses in NA
La Crosse Virus- Midwestern and eastern U.S. St. Louis Encephalitis Virus - Eastern and central U.S. Eastern Equine Encephalitis - Atlantic and Gulf Coast states Western Equine Encephalitis - Rural areas of western U.S.
West nile pop at risk
anyone living where mosquitoes are infected with West nile virus disease 60+ more susceptible to disease seasonality in US (June-September)
Yellow fever
arbovirus spread by Aedes aegypti mosquitoes affects tropical and subtropical areas of South America and Africa
West Nile Virus
arbovirus spread by mosquitoes an emerging infectious disease because increasing in # and geographic range can cause febrile illness, encephalitis, meningitis (inflammation of lining of brain and spinal cord)
Chickungunya virus
arbovirus transmitted to humans by bite of Aedes species mosquito
Prevention of Lyme Disease
best method: avoid the vector and bites from it know where to expect them: blacklegged ticks like moist, humid, environments in wooded/grassy areas walk down center of trails and avoid walking through vegetation apply insect repellent (DEET) to skin and clothing (protection for hours) apply insecticide (permethrin) on clothing or gear (protection through several washes) daily tick checks when returning from tick areas (yourself, clothing, pets)
Population for lyme disease
bimodal with peak in children (5-14) and adults (50-59)
Dengue transmission
bite of infected Aedes aegypti or Aedes albopictus to become infected = mosquito must feed during 5 day period when high levels of virus present in sick individual's blood 8-12 days for mosquito to transmit to another person mosquito infected for life
What happens with lyme disease?
blacklegged ticks will attach to host and suck blood slowly for several days, then drop off and prepare for next life stage if host animal infected with b. Burgdoferi, tick can ingest pathogen and become infected; if tick later feeds on human, transmission can occur longer attached, greater chance for transmission removal within 24 hrs greatly reduces risk once infected, tick can transmit for life
Lyme disease
borrelia burgdorferi motile, helical, gram-negative spirochetal bacteria maintained in zoonotic cycles involving variety of wild mammals and birds as reservoirs (white-footed mouse)
Mosquito borne encephalitis in US
cases quite rare most infected individuals asymptomatic symptoms include fever, headache, nausea, vomiting with potential progression to neuroinvasive disease (encephalitis) testing--detection of virus-specific IgM antibodies supportive treatment
Dengue Diagnosis
definitive diagnosis requires: - lab testing via isolation of virus (PCR) or - identification of dengue-specific IgM antibodies (ELIZA)
Dengue prevention
destroy sites where larvae develop (water filled containers in and around home)
Yellow fever testing
detection of yellow fever specific IgM antibodies
Dengue
disease caused by one of 4 closely related dengue viruses most important arthropod-borne viral disease of humans worldwide prior to 20th century = relatively minor, geographically restricted disease past 30 years = frequency of epidemics increased substantially in most tropical countries in American region US travel associated dengue cases occur and limited outbreaks most cases in US citizens from endemic transmission in US territories??
Where is WNV transmission?
documented many parts of world (Europe, Middle East, Africa, India, parts of of Asia and Australia) first detected in NA in 1999 and has spread across US and Canada
What is the distribution of VBD determined by?
environmental and social factors urbanization climate change globalization of travel and trade
EM rash
erythmea migrans begins at site of bite about 7 days after expands gradually over period of days red border with clearing center (bulls eye) warm nut not itchy or painful
Yellow fever acute phase
fever severe headache muscle aches nausea and vomiting x 3 days most improve
Where is chickungunya virus
first in Tanzania in 1952 since then, numerous epidemics in Africa, India, and southeast Asia 2013 identified in Americas on Caribbean islands
Clinical Manifestations (early)
for 3-30 days flu-like symptoms: fever, chills, malaise, stiff neck, headache
Where are Aedes found?
in and around homes bite any times, esp during the day
Yellow fever clinical illness
inapparent illness to clinical illness ratio = 7:1 3-6 day incubation period
Chickungunya virus clinical illness
incubation 3-7 days most affected are symptomatic with abrupt onset of fever, severe joint pain, joint swelling, rash, headache looks like Dengue improvement within a week
Vector-Borne Disease
infections transmitted to humans by the bite of an infected arthropod species (vector)
Extrinsic incubation period
interval between infection of vector when blood ingested from viremic host until virus appears in the salivary gland of the arthropod about 6-10 days for most arboviral infections
What is the lack of dengue transmission in continental US due to?
limited contact between people and vectors--too infrequent to sustain transmission
Post-Treatment Lyme Disease Syndrome
lingering symptoms of fatigue, pain, and joint or muscle aches following treatment which can last 6 mos or longer exact cause unknown
Vectors
living organisms that can transmit infectious diseases between humans or from animals to humans many bloodsucking insects--> ingest disease-producing microorgs via blood meal from human or animal host, and later injefct microorg into new host during subsequent blood meal
Risk factors for lyme disease
living, working, vacationing in a woodsy, rural environment
Where is dengue endemic?
many areas of the tropics and subtropics cases occur annually, typically when rainfall is optimal for Aedes breeding also a risk for epidemic dengue in these areas - large number of individuals infected over short-period of time - epidemics require a large number of vector mosquitoes, large number of individuals not immune to one of four virus types, and opportunity for contact between the two
Dengue Hemorrhagic Fever
more severe form of dengue involving damage to blood vessels leading to bleeding and fluid accumulation mortality of 5-15% if untreated
Common vectors and diseases they transmit
mosquitoes: west nile virus, malaria, dengue fever, zika virus disease tickes: lyme disease, rocky mountain spotted fever fleas: plague
Epidemiology of Lyme Disease
most commonly reported vector-borne illness in US incidence varies between geographic regions - prevalence of Ixodes ticks and proportion infected - opportunity for human exposure to infected ticks
Chickungunya treatment
no specific treatment supportive treatment--pain and fever management
Dengue Treatment
no specific treatment supportive treatment--pain and fever management and hydration
West Nile Treatment
no specific treatment supportive treatment--pain and fever management and hydration
Yellow fever treatment
no specific treatment supportive treatment--pain and fever management and hydration
Where is ixodes scapularis found?
northeast and upper midwest of US southern Canada I. pacificus primary vector along pacific coast of NA
Yellow fever vaccine
recommended for those aged 9+ months who are travelling to or living in areas at risk for yellow fever virus transmission (reemerged Africa and South Africa)
Where is lyme disease endemic?
several areas of US (Northeast, upper Midwest, Pacific coast) Canada eastern/central Europe and Russia
When does transmission peak for lyme disease?
spring/early summer when ticks most abundant and active
What is the laboratory testing for lymes?
step 1--enzyme immunoassay (EIA) test if negative = no further testing if positive = step 2 step 2-- immunobiot (Wester blot) test if negative = negative for lymes if positive = positive for lymes
Dengue Clinical Information
symptoms begin 4-7 days after bite and last 3-10 days high fever, severe headache, muscle, bone, and joint pain, rash
Arboviruses timing
temperate climates = seasonal in nature tropics = year round
Transmission of lyme disease
ticks don't fly, hop, or jump questing--walk to ends of grass or tree leaves and wave front legs in air until suitable host brushes past can attach to any part of human body but prefer hard to see areas like scalp, groin, armpit
West Nile 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 of lyme disease
uncomplicated cases = 2-4 weeks of oral antibiotics patient with cardiac or neurologic symptoms = IV antibiotics patients treated early typically recover quickly and completely
How to Remove Tick
use fine tipped tweezers as soon as it is noticed
West Nile Transmission
vector = mosquitoes (primarily Culex species) reservoir = birds "dead-end" hosts - humans and horses non-mosquito routes = blood transfusion, organ donation, transplacentally, and breastfeeding
Chickungunya testing
virus isolation, pcr chickungunya virus specific IgM antibodies contact state lab or CDC
Clinical manifestations (late)
weeks-months arthritis--60% carditis (inflammation of heart tissue) --5-16% neurologic complications (meningitis, encephalitis, cranial nerve palsies, nerve pain) --10-15% generalized EM rash
Primary host for immature I. scapularis
white footed mouse develops persistent infection with B. burgdorferi will feed on humans and can transmit lyme disease
Primary host for adult I. scapularis
white-tailed deer will feed on humans and can transmit lyme disease
