W9: Vector-Borne Diseases

tick-borne diseases

Lyme, RMSF

mosquito-borne diseases

malaria, Zika, West Nile

lyme disease

caused by Borrelia burgdorferi, a spirochete transmitted by tick bite; tick must be embedded for >24 hours and usually transmitted by nymph stage, in spring or early summer

what are the stages of lyme disease?

1: localized infection that causes erythema migrans or "bull's eye" rash

2: disseminated infection that causes systemic symptoms of fever and myalgia, secondary EM, meningitis, carditis with AV block and cardiomegaly, CN involvement with Bell's palsy

3: late persistent infection with arthritis and continuous neurologic problems occurring months to years after initial infection

what is needed to diagnose lyme disease?

history of tick bite and rash that is consistent with disease

what serologic tests can be used to diagnose lyme disease?

antibodies to B. burgdorferi (but do not appear until 2-4 weeks after infection)

lyme disease management

oral doxycycline or amoxicillin for early disease, IV cephalosporins for advanced disease

how can patients prevent lyme disease?

wear protective clothing, use DEET-containing insect repellant for skin or permethrin-containing tick-killing spray for clothing, check for and remove attached ticks

rocky mountain spotted fever (RMSF)

caused by coccobacillus rickettsia rickettsii transmitted by dog or wood tick; symptoms start within 2 days to 2 weeks of bite with prodrome of flu-like symptoms including malaise, loss of appetite, chills, fever, photophobia, and nausea

how does rash appear for RMSF?

red macules and papules develop starting on the wrists and ankles and spreading inward to involved the trunk; rash becomes hemorrhagic and purpuric often involves the palms and soles

which patient populations have a higher incidence of RMSF?

children and men

which condition is empiric treatment reasonable?

RMSF

RMSF management

doxycycline or chloramphenicol

what is the most important parasitic disease in human and endemic in most of the tropics?

malaria

what mosquito-borne disease is a flavivirus?

west nile virus

what is most common fever in travelers returning from endemic areas?

malaria

what are the 4 species of the plasmodium parasite?

P. falciparum, P. vivax, P. ovale, P. malariae

malaria signs/symptoms

fevers, shaking chills, headaches, myalgias, jaundice, n/v

malaria clinical course

incubation period is 9-40 days; prodrome of headache and fatigue followed by fevers, chills, and sweats; fevers often occur in regular cycles with patients appearing remarkable well between cycles

what is severe disease seen almost exclusively well?

P. falciparum

what can severe malarial disease include?

cerebral malaria, renal dysfunction, ARDS, DIC, severe anemia, can be fatal

what is gold standard for malaria diagnosis?

observation of parasite on blood smear

malaria diagnostics

observation of parasite on blood smear, rapid diagnostic tests, confirmation by PCR

malaria treatment

many antimalarial drugs and chloroquine is mainstay treatment

what prevention medications can be used for malaria?

chloroquine

what can west nile virus cause?

neuroinvasive disease (meningitis or encephalitis) which can be fatal

zika virus

arthropod transmitted flavivirus that usually causes mild, self-limited disease after an incubation of 3-12 days; symptoms of rash, fever, arthralgia, HA, and conjunctivitis lasting 2-7 days

who is zika virus most concerning in?

pregnant women due to association with birth defects (especially microcephaly and ophthalmologic abnormalities)

what infection can complicate zika virus?

GBS

zika virus diagnosis

zika virus RNA can be isolated from serum using PCR with highest sensitivity during 1st week of illness, after 1st week serologic testing for antibodies with ELISA may be done

who should be tested for zika virus?

all pregnant women should be screened for travel history then if symptomatic, tested

what should all pregnant women receive regardless of symptoms or test results if they have a positive travel history to zika area?

fetal ultrasonography and if anomalies detected, f/u with amniocentesis

rabies

viral encephalitis transmitted by saliva of infected animals including canines, bats, cats, raccoons, and skunks; incubation 10 days to years

rabies presentation

prodrome: 2-10 days of fever, malaise, flu-like symptoms, paresthesias, pain and intense itching at inoculation site

acute neurologic period: 2-7 days of fasciculations, priapism, focal or generalized seizures (furious rabies and paralytic rabies)

coma: respiratory failure, ARDS, cardiac arrhythmias, death

furious rabies signs/symptoms

agitation, hyperactivity, restlessness, thrashing, biting, confusion, hallucinations

paralytic rabies signs/symptoms

fever, headache, paralysis

rabies exam findings

autonomic instability with fever, tachycardia, postural hypotension, anisocoria, salivation, laryngeal spasm

rabies diagnostics

nuchal skin biopsy, corneal touch impression, viral culture and PCR of bite, saliva and CSF, brain biopsy postmortem

rabies management

done if there is suspected contact with. bat, skunk, or raccoon; unvaccinated individuals receive HRIG + rabies vaccine while vaccinated individuals receive post-exposure revaccination

botulism

not an infectious disease; paralytic disease caused by neurotoxin produced by Clostridium Botulinum (anaerobic gram-positive spore-forming rod)

what are the 3 major forms of botulism?

infant (intestinal): ingested food contains spores that germinate in intestine and produce toxin

food-borne: toxin produced in improperly canned or home prepared foods

wound: contaminated wound with soil, injection drug user (e.g. black tar heroin) and c-section wounds

botulism clinical presentation

GI symptoms followed by descending paralysis and anticholinergic symptoms; n/v, dry mouth, cranial nerve paralysis, ileus, urinary retention, muscle weakness, incoordination, respiratory muscle weakness

botulism management

antitoxin with high clinical suspicion