155. Zoonotic Infections


Diseases naturally transmitted between vertebrae animals and humans by contact, ingestion of contaminated water, or thru arthropod vectors (tick MCC). Risk factors: agricultural workers, animal processing workers, outdoorsmen, pet owners, vets, immunocompromised.

General viral illness vs tick-borne illness: consider in flu-like syndrome with either thrombocytopenia, elevated LFTs, or hyponatremia.

Tick Removal: apply viscous lidocaine to kill the tick and anesthetize the bite. Then use tweezers and pull upward from the closest point to the skin that the tick has attached to. Avoid crushing body. Then clean the surface of the skin off with disinfectant.

Rocky Mountain Spotted Fever

Caused by Rickettsia rickettsii. Vector is dermacentor tick. Peak between April and September. Most severe tick disease; mortality 5-10%. Around mid-Atlantic region: North Carolina, South Carolina, Tennessee, Oklahoma, Arkansas.

Clinical Features: fever, headache, myalgias, malaise; also get lymphadenopathy, nausea/vomiting, hepatosplenomegaly, conjunctivitis, renal failure, respiratory failure. Rash occurs 2-4 days after fever – blanching erythematous rash that becomes petechial later. Begins usually on hands,feet,wrists,ankles that then spreads centripetally.

Testing/Treatment: IgG/IgM antibodies not present in acute phase. Nonspecific neutropenia, thrombocytopenia, elevated LFTs, hyponatremia. Tx with doxycycline 100mg BID x 5-10d both for adults and children (recommended by AAP and CDC – insignificant teeth staining with one abx course)

Lyme Disease

Bug: Borrelia burgdorferi (spirochete), Vector: Ixodes scapularis (black legs). Endemic areas: Northeast and Wisconsin/Minnesota



Clinical Features: Stage I (days to week, typically 7 days after bite): fever (should be low grade), myalgias, athritis, headache, sometimes RUQ tenderness. Can have elevated transaminases. 90% will have classic rash: erythema migrains. Erythematous macular/papular rash with central clearing, though do not necessarily have to have central clearing. Stage II (weeks to months): neurologic abnormalities – bilateral Bell’s palsy, meningitis/encephalitis, peripheral neuropathies. Cardiac abnormalities as well – various AV blocks, myocarditis. Later late stage has migrating oligoarthritis usually in larger joints such as knee. Post-treatment Lyme disease syndrome: aches/pains, cognitive problems – difficulty thinking, stuttering. Can occur even after correct treatment.


Testing/Treatment:  Clinical suspicion. Tests are basically pointless in the ED, except for possible Stage II or later disease. Two Tier system: Do ELISA (checks for antibodies, very sensitive) first, then if positive, do Western Blot (checks for antigens) of either IgM (earlier) or IgG (later). PCR, urine all useless. Adults, non-pregnant, non-lactating, kids > 8yo: Doxycycline 100mg BID x 3 weeks. Allergy or other populations: Amoxicillin 500mg TID x 3 weeks (kids 30mg/kg/day), PCN, cefuroxime, azithromycin. Stage II usually needs longer course.

Prophylaxis: NEJM 2001: 3.2% of placebo group got Lyme vs 0.4% of treated group. 1 in 33 chance of getting Lyme disease with tick bite in endemic area. CDC recommendations for prophylaxis: tick on for > 36 hrs, ixodes tick, endemic area, < 72 hrs since bite. Chance of getting Lyme disease with time of exposure: 0% at 24 hrs, 12% at 48hrs, 79% at 72hrs, 94% at 96hrs. Doxycycline 200mg x 1 only. No studies have shown benefit with amoxicillin. Unable to give in kids < 8.


Bug: Ehrilicia genus. Vector: lonestar tick, Amblyomma americanum. Usually from white-tailed deer in southeast US.

Clinical Features: begin 10-14d after bite. Fever, headache, malaise, N/V, diarrhea, abdominal pain, arthralgias. Can develop severe renal failure, respiratory failure, encephalitis. Labs: leukocytopenia, thrombocytopenia, elevated LFTs.

Testing/Treatment: Diagnosis clinical, though can watch for rise in antibodies from acute to chronic phase. Tx with doxycycline for both adults and kids.


Bug: Anaplasma phagocytophilum. Vector: black-legged tick, Ixodes scapularis. Geography: upper mid-Atlantic, north-central states, northern California. Transmission usually in the summer.

Clinical Features: similar to ehrlichiosis or flu: fever, chills, headache, myalgias. Labs: leukocytopenia, thrombocytopenia, elevated LFTs.

Testing/Treatment: clinical diagnosis, again can be confirmed with rise in antibodies over time. Tx with doxycycline.

Tickborne Relapsing Fever

Bug: Borrelia spirochete. Vector: Ornithodoros ticks (soft ticks). Present with rash/eschar which then turns into fever/chills/cephalgia, myalgia, arthralgia, abd pain. Usually have leukocytosis and thrombocytopenia. Diagnosis spirochetes on Wright-Giemsa-stained peripheral smear. Very rare diagnosis. Tx with doxycycline or erythromycin.

Colorado Tick Fever

Bug: Coltivirus. Vector: wood tick, D. andersoni. Only in mountainous regions with elevation > 4000ft. Fever/chills, headache,myalgias, photophobia. May have macular/petechial rash. Have relative leukopenia. Tx supportive.


Bugs: Babesia microti and Babesia equi. Vector: Ixodes tick as well as blood transfusions. Present with fever, chills, malaise, intermittent sweats, myalgias, headache, and hemolytic anemia. Looks like malaria/erlichiosis. Labs: anemia, elevated LFTs, thrombocytopenia, renal failure. 20% will also have Lyme disease. Diagnosis with Giemsa-stain peripheral blood smear. Tx: atovaquone + azithromycin or clindamycin + quinine x 7-10d.

Zoonotic Encephalitis

Vector usually mosquito or tick. Usually present with fever, myalgias, malaise; then progresses to headache and decline in mental status. CSF: elevated opening pressure, lymphocytes. Viral culture usually negative. Diagnosis made by serum ELISA.

West Nile Virus: can cause flu-like syndrome or encephalitis.  Tx supportive.

Other causes of zoonotic meningitis: brucellosis, listeriosis, plague, salmonellosis, tularemia, leptospirosis, Lyme dx, ehrlichiosis, Q fever, RMSF, psittacosis.

Zoonotic Respiratory Infections

Anthrax: Bacillus anthracis. Usuallly handling animal hides or imported raw wool. Fatal. Causes mediastinitis without alveolar involvement. Presents with flu-like illness that progresses to severe respiratory failure. Can get vaccine if in exposed population. Postexposure prophylaxis: 60d course of abx + 3 dose vaccine.

Brucellosis: ingestion of unpasteurized dairy products. Usually present with URI with cough, hoarseness, wheezing. Peritracheal/hilar lymph nodes, no infiltration on X-ray. Can chronically get granulomas and lymph nodes. Tx: doxycycline + rifampin x 6 weeks.

Psittacosis: parrot fever, parrot disease, ornithosis. Caused by chlamydia psittaci common in birds. Inhalation of bird droppings. Present with flu-like syndrome with nonproductive cough, lobar/interstitial infiltrates on X-ray. Looks like ‘typical’ atypical pneumonia. Tx: doxycycline 100mg BID or tetracycline 500mg QID.

Q fever: rickettsial infection by inhalation, no vector. Common in domesticated farm animals, usually in feedlots. Self-limiting pulmonary syndrome, though can get extra pulmonary symptoms (myo/pericarditis). Tx with doxycycline within 3 days for most effect.

Pasteurellosis: in normal oral flora of cat/dogs. Can cause necrotizing cellulitis, though can get bronchitis/pneumonia. Tx: Augmentin, tetracycline, PCN, cephalosporin.

Melioidosis: Caused by Burkholderia pseudomallei (gram negative saprophytic bacterium). Can be serious, but usually causes pneumonia, sometimes abscesses. Tx doxycycline or bactrim.

Pulmonic Plague: Yersina pestis. Usually in rock squirrels and rodents in the southwest. Vector: rodent flea. Usually get eschar at bite site with a bubo near it. Sepsis/pneumonia can occur next. Highly contagious in pulmonary form. Very fatal without tx. Tx doxycycline or cipro, gentamicin alternative.

Hantavirus: Sin Nombre virus, different vectors, usually deer mouse in southwest US. Usually infected by inhalation of rodent feces or by rodent bite. Worldwide usually present with acute kidney failure with thrombocytopenia, ocular abnormalities, flulike syndrome. In US, presents as flulike syndrome that turns into severe ARDS. High mortality 50-70%. Diagnosis by immunofluorescent or immunoblot assay. Tx supportive, inhalation ribavirin.

 Other Zoonotic Infections

Cutaneous Anthrax (woolsorters dx): usually close contact with livestock. Spores deposited into skin, usually arms/legs. Macule that turns into ulcer with multiple vesicles. Turns into eschar in a few weeks and then falls off. Vesicles are contagious. Tx does not help.

Helminths (worms): dogs are source for toxocara canis which causes toxocariasis. Usually subclinical, but can cause fever/cough/rash in children. Tx albendazole/mebendazole. Dipylidiasis (tapeworm): rare, but in children causes diarrhea and pruritus ani. Tx praziquantel or niclosamide.

Toxoplasmosis: can be infected by either ingesting uncooked meat, ingestion of oocytes from cat feces, and transplacentally. 10% infected fetuses have abnormality: retinochoroiditis, hydrocephalus, hepatosplenomegaly, thrombocytopenia. Tx pyrimethamine + sulfadiazine and folinic acid.

Clinical Cases


Tintinalli, Seventh Edition, Chapter 155: Zoonotic Infections

Crashing Patient, Scott Weingart, Tick Borne Illness, Reviewed 4/7/14

155. Zoonotic Infections

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