Tick-borne Disease Flashcards
what is questing behavior?
- ticks wander about the skin of the host for several hours before attaching
- larvae detect heat, movement and CO2
timing of tick disease transmission
-usu takes 24-48 hrs of attachment and feeding before transmission
what % of tick bites result in tick-borne infection?
1%
contents of tick saliva
- neurotoxins
- anticoagulants
- immunosuppressants
- anti-inflammatories
- pathogens: bacteria, viruses, nematodes
- toxins
RFs for ticks
- male
- children
- farmers
- exposure to dogs
- live in wooded area
- exposure!!!
RMSF classic presentation
- high fever
- HA
- petechial rash w/ hx of tick bite
RMSF mortality rate
if untreated, 30% mortality rate
rickettsia rickettsii
- gram neg. bacteria
- obligate intracellular parasite w/ tropism for human endothelial cells
- transmitted to humans through saliva while a tick is feeding
mechanism of injury in RMSF
- tick attached for many hours
- r. rickettsii enter skin
- spread via lymph to blood stream
- live inside vascular endothelial cells and multiply
- endothelial cells die, allowing blood to leak out of vessels into surrounding tissues
- sm. vessel thrombi and obstruction, fluid leakage causing edema, hypovolemia and low BP
S/Sx of RMSF
- sudden onset
- fever
- malaise
- severe frontal HA
- myalgia
- vomiting
(flu like so hard to diagnose)
RMSF incubation period
2-14 days (avg. 7)
RMSF rash
- 90% of pts get it - usu 3-5 days after bite
- blanching erythematous rash w/ macules that become petechial over time
- starts on wrists and ankles and spreads to trunk
- rash on palms and soles is characteristic but not present until later dz
- can be easily missed in dark skin
Ddx of RMSF
- viral illness
- drug allergy
- measles
- meningococcemia
- mono
- roseola
- fifth dz
lab detection of early RMSF
-nothing available for early RMSF –> dx based on clinical suspicion
clinical findings suggestive of RMSF
- thrombocytopenia: from increased destruction at sites of rickettsia mediated vascular injury
- elevated LFTs
- hyponatremia (50% of pts) d/t hypovolemia
rickettsial indirect fluorescent antibody (IFA) serum test
- recommended by CBC
- detects Abs in blood samples
- diagnostic Ab levels don’t appear until 7 days after onset
- confirmation = 4 fold change in titers
- Abs may persist for years
immunostaining for RMSF
- 3 mm punch bx of rash taken prior or w/i first 48 hrs after abx therapy
- not recommended by CBC - only 70% sensitive
Tx timing for RMSF
- DON’T delay tx for lab results or rash
- treat immediately if true suspicion
pharmacological tx for RMSF
- doxycycline 100 mg BID 3 days or more after fever subsides (min. 5-10d)
- failure to respond suggests wrong dx
outpatient vs. inpatient tx of RMSF
- outpatient: if mildly ill
- hospital: severely ill, complications, may take up to 5 days to become afebrile
important ADRs of doxycycline
- esophagitis (take w/ full glass of water)
- teeth discoloration: don’t use in kids < 8 yo
- photosensitivity
Complications of RMSF
- DIC
- skin necrosis
- cardiac arrythmias
- encephalitis
- GI bleed
- death w/o tx
what is the MC tick borne dz in the US and Europe?
lyme dz
bacteria in lyme dz
borrelia burgdorferi (spirochete)
tick vector for lyme dz
- deer tick (ixodes scapularis)
- most likely to transmit infection after feeding for 2 or more days
- reservoir is white tailed deer
tick vector for RMSF
- american dog tick (dermacentor variabilis) - in Eastern and South Central US
- rocky mt wood tick (dermacentor andersoni) - in mountain states west of the mississippi
pathophysiology of lyme dz
- borrelia in tick midgut –> salivary glands –> host
- then spirochetes disseminate from the bite site
3 ways spirochetes disseminate from bite site in lyme
- cutaneous - travel centrifugally
- lymphatic
- hematogenous routes
S/sx of lyme dz
- many feel mildly ill
- myalgia
- arthralgias
- fatigue
- neck stiffness
- low grade fever
- regional adenopathy
halmark of lyme dz
erythema migrans
erythema migrans
- slowly expanding bulls eye rash
- 40% have central clearing
- usu not painful or itchy
- common sites: popliteal fossa, gluteal fold, torso, axilla
- avg size: 15 cm
- if untreated, resolves in 3-4 weeks
early localized stage of lyme infection
- days to a month after infection
- erythema migrans and viral-like sx
early disseminated stage of lyme infection
- weeks to months after infection
- neurologic sequalae (facial palsy, meningitis)
- cardiac dz (conduction deficits, blocks)
- severe malaise
late stage of lyme infection
- months to yrs after infection
- migratory arthritis pain and swelling in asymmetric large joints (usually knee)
- cognitive deficits
- usu resolves w/i a few weeks or months of abx
- acrodermatitis chronica atrophicans (not really in US )
summary of sx of lyme
skin, joints, nervous, cardiac sx
Ddx of lyme dz
- changing mole
- cellulitis
- tinea
- granuloma annulare
- fixed drug erruption
- contact dermatitis
- spider bite
dx of lyme dz
-erythma migrans + pt present in endemic area
OR
-serology + extracutaneous manifestations of lyme dz
Lab detection of lyme dz
- ELISA or IFA
- if positive then western blot test for corroboration
tx of lyme dz
- doxycycline 100 mg BID
- duration depends on stage of dz
alternative tx for lyme dz
- amoxicillin 500 mg TID x 14 days
- cefuroxime 500 mg BID x 14 days
jarisch-herxheimer rxn
- rapid destruction of organisms w/ release of membrane into circulation
- intesification of sx w/ tachycardia and hypotension
- 12-24 hrs after treatment
- pts can confuse w/ allergic rxn
relapsing fever
- from bite of tick or louse infected w/ Borrelia
- rare
common location for relapsing fever
-associated w/ sleeping in rustic cabins in mountainous areas of western US, canada, africa, europe
sx of relapsing fever
- HA, muscle and joint aches and nausea
- recurrent, acute episodes of fever (up to 106) followed by periods of defeverscence of increasing duration
Dx of relapsing fever
-observation of Borrelia in blood smear, spinal fluid, or bone marrow of a symptomatic person
southern tick-associated rash illness (STARI)
- lyme like dz in southeaster and south central states
- not fully characterized
STARI tick vector
- ambylomma americanum (lonestar tick)
- aggressively bites humans
- unknown cause
sx of STARI
- erythema migrans w/i 7 days of bite; > 8cm
- mild clinical course: fatigue, fever, HA, muscle and joint pain
- NOT linked to chronic arthritic or neurologic sx
lab eval and tx of STARI
- lab: negative lyme test; no commercially available test
- tx: doxycycline 100 BID x 10 days
causative agent of ehrlichiosis
-ehrlichia chaffeensis: small gram negative bacteria that primarily invade leukocytes (monocytic)
AND
-anaplasma phagocytophilum (granulocytic)
ehrlichiosis tick vector
- lone star tick; amblyomma americanum (HME)
- blacklegged tick; ixodes scapularis (HGA)
- western blacklegged tick; ixodes pacificus
Hosts for ehrlichiosis
- coyotes
- mouse
- white-tailed deer
- horses (in OK)
pathophys of ehrlichiosis
bacteria infect either monocytes (HME) or granulocytes (HGA)
what is a characteristic of ehrlichiosis?
-morulae: bacteria divide w/i vacuoles inside leukocytes to form morulae
s/sx of ehrlichiosis
- hx of a tick bite
- most pts are asx
- incubation of 1-2 weeks
- rash is rare
- fever/HA
lab findings in ehrlichiosis
- leukopenia
- thrombocytopenia
- elevated LFT, LDH, and alkaline phosphatase
- indirect fluorescent antibody test is preferred diagnostic method
Ddx of ehrlichiosis
RMSF
complications of ehrlichiosis
- usually in immunocomrpomised
- renal failure
- disseminated intravascular coagulopathy
- meningoencephalitis
- adult respiratory distress syndrome
- seizures
- coma
tx of ehrlichiosis
- tx should not be delayed for labs
- doxycycline 100 BID x 10 days or for 3-5 days after defervescence
mortality in ehrlichiosis
-HME: 2-5%
-HGA: 7-10%
(probably overestimations)
tularemia (aka rabbit fever) bacteria
- francisella tularensis
- gram negative bacteria
tularemia tick vectors
- american dog dick: dermacentor variabilis
- lone star tick; amblyomma americanum
hosts for tularemia
rodents and rabits
epidemiology of tularemia
avg. 25 cases/yr in OK
how to become infected w/ tularemia
-begin bitten by infected tick (MC), deerfly or other insect
-handing infected animal carcasses
-cat scratch or bite
-eating/drinking contaminated food/water
-inhalation
(not person to person)
clinical presentation of tularemia
- usu in 3-5 days
- ranges from asx to septic shock and death
- the type is based on mechanism of entry of the organism
ulceroglandular type of tularemia
- 80%
- bacteria enters through scratch, tick bite, or abrasions
- fever, ulcer, lymphadenopathy
glandular type of tularemia
- similar to ulceroglandular but no skin lesion
- organism is presumed to enter via inapparent abrasion and then spreads
oculoglandular type of tularemia
- organism enters via conjunctiva of the eye (by splashing of blood or rubbing eyes)
- 1-2%
- painful, purulent conjunctivitis w/ preauricular or cervical lymphadenopathy
oropharyngeal type tularemia
- 1-4%
- after eating poorly cooked meat of an infected rabbit or drinking contaminated water
- sore throat, abd pain, n/v/d, occasionally frank GI bleed
pneumonic type tularemia
- from either inhalation or hematogenous spread
- MC in lab workers
- dry cough, dyspnea, and pleuritic chest pain
- can get pneumonia and/or ARDS
typhoidal type tularemia
- 10-15%
- more severe
- likely from bacteremia
- fever, chilles, myalgias, malaise, weight loss
- often present w/ pneumonia
dx of tularemia
- culture of organism from blood, sputum, wound (have to culture in cysteine)
- serology: 1:160 or higher titer is positive
tx of tularemia
-streptomycin 10mg/kg BID (IM) x 7-10 days
prognosis of tularemia
- mortality in untreated: 5-15%
- mortality in treated: < 4%
bioweapon potential of tularemia
- widely found in nature and relative easy to grow in lab
- used airborne, easy to spread
- highly infectious
- so vaccine is available for those at high risk
tick paralysis
- rare, but can be fatal
- removal of tick will usu begin recovery w/i hours
- female tick saliva contains neurotoxins that result in paralysis (localized to bodywide)
ticks implicated for tick paralysis
- dermacentor
- ixodes
- amblyomma
- usually attached 4-7 days before paralysis occurs
red meat allergy tick vector
lonestar tick; ambylomma americanum
patho of red meat allergy
- carb produced in the gut of a tick and found in red meat and some dairy –> Alpha-Gal
- repeated exposure to the sugar induces an allergy to it and the person can no longer tolerate red meat
sx of red meat allergy
urticaria to anaphylaxis
evalulation for tick-borne dz after tick bite
- size: the more engorged, the more likely bacteria passed through saliva
- can’t pass bacteria if not attached
- consider if endemic area
- rash?
- length of time attached
