Vector-Borne Disease

Vector-Borne Disease

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

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

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

What is the distribution of VBD determined by?

environmental and social factors

urbanization

climate change

globalization of travel and trade

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)

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

Where is ixodes scapularis found?

northeast and upper midwest of US

southern Canada

I. pacificus primary vector along pacific coast of NA

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

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

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

Clinical Manifestations (early)

for 3-30 days

flu-like symptoms: fever, chills, malaise, stiff neck, headache

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

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

Diagnosis of Lyme disease

Clinical presentation--EM rash is characteristic and history of potential infected tick exposure supports diagnosis

Laboratory testing

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

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

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

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

Where is lyme disease endemic?

several areas of US (Northeast, upper Midwest, Pacific coast)

Canada

eastern/central Europe and Russia

Population for lyme disease

bimodal with peak in children (5-14) and adults (50-59)

When does transmission peak for lyme disease?

spring/early summer when ticks most abundant and active

Ratio of inapparent to apparent for lymes

1:1

Risk factors for lyme disease

living, working, vacationing in a woodsy, rural environment

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)

How to Remove Tick

use fine tipped tweezers as soon as it is noticed

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

Arboviruses timing

temperate climates = seasonal in nature

tropics = year round

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

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??

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

Where are Aedes found?

in and around homes

bite any times, esp during the day

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

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

Dengue Diagnosis

definitive diagnosis requires:

- lab testing via isolation of virus (PCR) or

- identification of dengue-specific IgM antibodies (ELIZA)

Dengue Treatment

no specific treatment

supportive treatment--pain and fever management and hydration

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

What is the lack of dengue transmission in continental US due to?

limited contact between people and vectors--too infrequent to sustain transmission

Dengue prevention

destroy sites where larvae develop (water filled containers in and around home)

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)

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

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

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 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

West Nile Treatment

no specific treatment

supportive treatment--pain and fever management and hydration

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

West Nile Incubation period

2-6 days (range of 2-14)

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)

West nile transmission cycle

Yellow fever

arbovirus spread by Aedes aegypti mosquitoes

affects tropical and subtropical areas of South America and Africa

Yellow fever clinical illness

inapparent illness to clinical illness ratio = 7:1

3-6 day incubation period

Yellow fever acute phase

fever

severe headache

muscle aches

nausea and vomiting x 3 days

most improve

Toxic phase

15% of cases progress to this phase

high fever

jaundice, bleeding, shock and organ failure with 25-50% mortality

Yellow fever testing

detection of yellow fever specific IgM antibodies

Yellow fever treatment

no specific treatment

supportive treatment--pain and fever management and hydration

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)

Chickungunya virus

arbovirus transmitted to humans by bite of Aedes species mosquito

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

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

Chickungunya testing

virus isolation, pcr

chickungunya virus specific IgM antibodies

contact state lab or CDC

Chickungunya treatment

no specific treatment

supportive treatment--pain and fever management

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

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.