BITES, STINGS, AND TOXIC EXPOSURES
| INFECTIONS DUE TO INSECT BITES AND ANIMAL EXPOSURES —Richard H. Glew, MD, Professor of Medicine,
Molecular Genetics, and Microbiology, University of Massachusetts Medical School, and Vice Chair, Medicine-Undergraduate
Medical Education and Faculty Affairs, University of Massachusetts Memorial Medical Center, Worcester, MA
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| Babesiosis: cattle definitive host; caused by Babesia divergens or Babesia bovis; causes disease in compromised humans
(eg, splenectomized person); cycle similar to that of ticks (eg, Ixodes scapularis; nymph stage feeds on humans) found
outdoors in warm weather that cause anaplasmosis and Lyme disease; presentation—usually asymptomatic; more common
in people of middle and advanced age; incubation period ≤3 wk; fever of unknown origin; malaise; myalgia; arthralgia;
headache; hepatosplenomegaly; anemia; thrombocytopenia; diagnosis—blood smear; 10% to 50% of red blood cells
parasitized; difficult to identify on slide; treatment—clindamycin and quinine; quinine poorly tolerated; high doses of
clindamycin produce severe dyspeptic symptoms; atovaquone and azithromycin; treat for 10 to 14 days until patient asymptomatic
and blood smear clear
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| Transmission of Toxoplasma gondii: ingestion of raw or undercooked meat—trophozoite (active vegetative form)
spreads from cell to cell; cat feces containing oocysts soils grazing area; tissue cysts dormant in flesh of infected grazing animal
account for 99% of transmission; can also be due to ingestion of milk of acutely infected grazing animals or poorly or
minimally processed cheese; cats—litter box source of T gondii; oocysts in acutely infected cat usually shed in few weeks;
cysts require ≈5 days of drying to become infectious; may not be problem if litter box emptied frequently; insects can land in
litter box and contaminate eating surfaces; congenital transmission—by acutely infected pregnant woman to fetus; antibody-positive
women at time of entering pregnancy not at risk of transmitting toxoplasmosis to infant; organ
transplantation—kidney or heart transplant from positive donor can cause acutely acquired toxoplasmosis in transplanted
patient
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| Toxoplasmosis: acute acquired toxoplasmosis asymptomatic 95% of time; some patients develop regional or systemic lymphadenopathy
with mild constitutional symptoms or progress to illness similar to full-blown infectious mononucleosis;
usually self-limited; may take weeks or months to resolve; patients almost never warrant treatment (cumbersome and
moderately dangerous); congenital toxoplasmosis—if acute toxoplasmosis diagnosed in pregnant woman, assess
whether transplacental transmission occurred; drug therapy may result in damage to fetus; termination of pregnancy often
recommended; consequences include toxoplasmosis, other viruses (eg, syphilis), rubella, cytomegalovirus, and herpes
simplex virus (TORCH) complex; microcephaly; brain damage; macrocephaly due to hydrocephalus; hepatosplenomegaly;
fever; anemia; chorioretinitis common (often not diagnosed until child reaches verbal stage); immunocompromised
host—dormant infection reactivated; estimated 25% of individuals infected with Toxoplasma; patients with HIV infection
with advanced AIDS, history of transplantation, lymphoma, high-dose corticosteroid therapy; use of anti-tumor necrosis
factor (TNF) drugs (eg, infliximab [Remicade], etanercept [Enbrel], adalimumab [Humira]) may cause reactivation
(patients often have cryptococcosis, miliary tuberculosis, and Pneumocystis pneumonia)
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 | Pathology: multifocal necrotizing encephalitis; headache; altered mental status; fever; circumferentially intensified round
lesions on computed tomography; number one diagnosis toxoencephalitis, followed by central nervous system lymphoma
and nocardiosis; vessel occlusion and infarction of parts of brain
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| Diagnosis and treatment: baseline serology in patients entering immunosuppressed state; positive IgG indicates latent infection
(consider prophylactic treatment); for acute toxoplasmosis, test for IgM; severely immunosuppressed patients
may have lost ability to make antibodies to new and old pathogens; confirmatory brain biopsy in patients with encephalitis;
treat patients who have advanced HIV, headache, fever, altered mental status, known antibody positivity, and
multifocal lesions in brain (if no improvement in 2 wk, discuss neurosurgery or interventional radiology; perform biopsy
to rule out lymphoma or nocardiosis); sulfadiazine and pyrimethamine primary therapy; sulfadiazine and trimethoprim
used as prophylaxis for Pneumocystis in HIV patients with CD4 count <200/mm3 ; in patients with sulfa
allergy, use clindamycin and pyrimethamine; spiramycin (difficult to obtain); immunologically normal patients usually
not treated; treat persistent symptoms until patients asymptomatic (4-6 wk); patients permanently immunosuppressed
treated acutely aggressively for 6 wk, then placed on lifetime suppression
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| Cryptosporidiosis: caused by gastrointestinal (GI) protozoa; widely distributed in mammals, birds, and reptiles;
transmission—men having sex with men; diaper to hands to mouth in day care centers; pathogen not susceptible to chlorine
(water filtration required); organism not invasive in immunologically normal individuals; causes villus atrophy, malabsorption,
and inflammation in submucosa; presents with malabsorptive diarrhea, anorexia, and weight loss; self-limited
in 2 to 3 wk; diagnosis—difficult to identify; internal morphology usually not visible in trichrome stain; rule out by performing
modified acid-fast stain (Kinyoun carbolfuchsin stain); laboratory study must be requested (routine ova and parasites
study does not include Cryptosporidium); treatment—nitazoxanide (Alinia) or azithromycin (“neither very
effective”)
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| Giardiasis: Giardia lamblia widely distributed; common in beavers and nutrias; cysts not susceptible to chlorine; consider
giving metronidazole for presumptive use for patients traveling to high-risk areas (eg, Eastern Europe); incubation period 1
wk to 10 days; syndrome—upper GI symptoms; eructation; burping; nausea; stomachache; anorexia; weight loss due to
anorexia and malabsorption; watery diarrhea; nonpurulent diarrhea (not bloody); fatty stools; flatulence; immunocompromised
patients (particularly with immunoglobulin deficiencies) may have persistent or repeated infections; trophozoite
rarely seen in stool; obtain upper GI sampling with frank upper GI endoscopy and/or perform biopsy of duodenum; antigen
test 95% sensitive; cure rate, 75%; can be difficult to eradicate
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| Questions and answers: coinfections with babesiosis, Lyme disease, and anaplasmosis—≥25% of ticks usually coinfected
with Lyme disease and anaplasmosis; symptomatic babesiosis uncommon; in humans, coinfection presumed; oral
tetracycline preferred over β-lactam for Lyme disease; polymerase chain reaction (PCR) testing for babesiosis—
consider rechecking blood smear in patients with positive PCR test result and negative blood smear result; PCR detects
patients who are mildly ill; giardiasis—associated with contamination (by wild animals) of remote nonmunicipal water
supplies and/or shallow drying wells; documented cases of intrafamilial spread with no remote travel and no suspicious
water consumption, and transmission through day care centers
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| PROBLEMS RELATED TO PET BITES AND SHELLFISH —Dr. Glew
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| Pet bites: dog bites—10% become infected; common on face; dogs tend to rip and tear (open wound can be cleaned, irrigated,
and drained; traditionally, only face and hand wounds sutured loosely); bacterial flora include Staphylococcus aureus
and Pasteurella species; cat bites—≈33% become infected; lancinating; cats tend to bite and grip on distal upper
extremities; Pasteurella multocida has short incubation period (<24 hr; polypharmacy not required); in patients with local
inflammatory findings (redness, swelling, warmth, tenderness, pain, immobilization), consider whether orthopedic structures
affected; if no resolution after 24 hr of antibiotic therapy and elevation, deep orthopedic soiling likely; therapy for
cat bites—intravenous (IV) ampicillin for severe infections; amoxicillin; ceftriaxone; fluoroquinolones; therapy for dog
bites— β-lactam and β-lactamase inhibitor combination (eg, ampicillin and sulbactam, piperacillin and tazobactam, or
ceftriaxone and metronidazole)
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| Necrotizing soft tissue infections: systemically fatal and locally necrotizing; must be detected promptly; patient must
be placed in intensive care unit (ICU) for adequate pressor and fluid support and debridement by surgeon; self-perpetuating;
tissue must be debrided promptly, aggressively, and repeatedly; clinical findings—patient “looks terrible”; red extremities;
chills; fever; malaise; depressed mental status; problems with blood pressure and urine output; marked
leukocytosis or leukopenia with large left shift; color other than red; eschar; crepitus; free squeezable fluid in deep tissue
planes that can be blotted; vesicles or bullae filled with anything other than clear fluid; pain out of proportion to physical
examination; anesthetic effects (perforating sensory nerves “wiped out”)
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| Capnocytophaga canimorsus: affects asplenic patients, patients with cirrhosis (particularly alcoholic cirrhosis), patients
with hemochromatosis, and immunosuppressed patients; infections occur from dog bites or if dog licks wound; starts as
cellulitis then rapidly becomes gangrenous; patients develop high-grade bacteremia early, then secondary metastatic skin
lesions with full-blown sepsis and multiorgan failure; often susceptible to fluoroquinolones
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| Vibrio vulnificus: associated with shellfish; infection usually result of incurring wound in brackish water (eg, stepping on
sharp rock) or exposing open wound to salt water; risk factors—cirrhosis; asplenic state; polymorphonuclear leukocyte
dysfunction (or low count); leukemia; lymphoma; chronic metabolic disease; advanced end-stage renal disease; wound
infection starts as cellulitis and becomes necrotic; patients develop bacteremia and secondary necrotic skin lesions; patients
can develop full-blown sepsis with multiorgan failure and die; variant associated with ingestion of raw shellfish;
treatment—aggressive debridement by surgeon; tetracycline and third-generation cephalosporin (eg, cefotaxime, ceftriaxone);
fluoroquinolones; aminoglycoside may be added during first 1 to 2 days; fluid and pressor management in ICU
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| Erysipelothrix rhusiopathiae: also known as Erysipelothrix insidiosa; gram-positive bacillus, found on and in fish and
shellfish; seen in fishermen injured by sharp instruments and butchers who handle pork or poultry products; wound does
not respond to antistaphylococcal and antistreptococcal antibiotics (eg, oxacillin, nafcillin, or first-generation cephalosporins);
small lesion becomes crusted and ulcerated; “somewhat focal” cellulitis develops around ulcer and spreads
proximally with lymphangitis; may stop at lymph node changes and lymphadenitis; no improvement with routine antibiotics
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| Tetanus prophylaxis: 3 primary injections (at 2, 4, and 6 mo of age) and 1 booster injection suggested to provide immunity
for life; booster injection more frequently than every 10 yr not necessary; in people born before 1935, give first
tetanus injection (primer; followed by 2 more, each 1-2 mo apart) with tetanus immune globulin; people from emerging
or midrange economic countries who do not provide immunization records should be given tetanus, immune globulin,
and 3 booster injections
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| Rabies vaccines: 3 vaccines available; use vaccines derived from human cell cultures; murine brain vaccine—
commonly used; inexpensive; effective; 15% risk for allergic encephalitis; vaccines expensive ($150-$875/dose in
United States); safe; rabies immune globulin important for postexposure prophylaxis; regimen—1 mL on days 0, 3, 7,
14, and 28; human rabies immune globulin (RIG), 20 IU/kg (≈10 mL for average adult of 70-80 kg); injected in and
around wound to inactivate virus locally (remainder injected at remote site); indications—patient bitten by wild or feral
animal not “brain-proven negative” for rabies; start prophylaxis (RIG and first of vaccines); discontinue after 1 to 2 days
if brain test negative; domestic animals become ill within 10 days; most rabies in northeastern United States bat variant
(when exposed to bat, recommended to capture bat for evaluation, or person committed to immunization)
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| SPIDERS, STINGRAYS, AND RATTLESNAKES —Aaron Schneir, MD, Associate Professor, Department of Emergency
Medicine, University of California, San Diego, School of Medicine
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| Brown recluse spiders: nocturnal; bites painless; diagnosis highly suspect outside of endemic areas (misdiagnosis
common); necrotic wounds may require skin grafting; most patients recover with no scarring or complications; no definitive
or proven treatment; infection unusual; management—dapsone suggested beneficial; rule out other causes; wait for
wound margins to demarcate and consider skin grafting
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| Black widow spiders: easy to identify (black with red hourglass shape); venom—α-latrotoxin can cause massive exocytosis
of neurotransmitters; release of acetylcholine leads to pain in localized muscle groups, systemic pain, and localized
or diffuse diaphoresis; release of norepinephrine causes tachycardia and hypertension; envenomations occur during
various times of day; bites painful; presentation—punctate lesion surrounded by blanching of skin and erythema seen
30% of time; pain can be intermittent; pain treated with medication may return and last for few days; death highly unusual,
particularly in United States; myocarditis, atrial fibrillation, and myocardial infarction (MI) rare; priapism reported
in children (rare; responds to antivenin); management—horse-derived antivenin can cause immunogenic response (consider
risks [eg, anaphylactic reaction]); local wound care; treat pain with, eg, opioids or benzodiazepines (not unusual for
patients to return to emergency department [ED] with more pain; syndrome can last for 2 days); calcium salts (eg, calcium
gluconate or calcium chloride, IV) considered beneficial and used frequently (little supportive evidence);
antivenin—appears effective (patients often discharged from ED); one described death with undiluted antivenin in pediatric
patient with known history of asthma and allergies to medications; explain risks and benefits of treating bite (not
life-threatening); appears efficacious when given late (eg, 90 hr after envenomation); safe in pregnancy (little data available)
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| Stingrays: shuffling feet when entering water recommended; envenomation occurs when stingrays feel threatened; when
stepped on, stingrays whip spine, and envenomate dorsal aspect of foot; spine serrated, sharp, and surrounded by tegumentary
sheath where venom found; sheath and spine can become embedded (reasonable to search for spine); need for antibiotics
uncertain and likely depends on water; serious infections occasionally described; severe pain resolves quickly;
systemic effects uncommon; treatment—local wound care; need for x-ray and prophylactic antibiotics uncertain; immersion
in hot water suggested to inactivate enzymes and appears effective in relieving pain; medication for refractory pain;
use of prophylactic antibiotics to cover Vibrio infections not well-established
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| Rattlesnakes: most bites incurred while playing with pet rattlesnakes; venom contains procoagulants, anticoagulants, metallic
ions, and neurotoxins; ≈20% of bites dry (ie, no local or systemic signs of envenomation; observe patients for 6-8 hr);
clinical syndrome—death uncommon; local tissue destruction and swelling most prominent and concerning (eg, may result
in loss of fingers); neurologic dysfunction (eg, fasciculations); hematologic effects (eg, decrease in platelets and fibrinogen);
management—document and follow degree of swelling (determines need for antivenin); swollen forearm does not indicate
compartment syndrome (treatment with prophylactic fasciotomy results in poorer outcome [cosmetically and functionally]
than with supportive treatment and antivenin); deaths—1 to 2 per year in United States; loss of airway from, eg, bite on
tongue; anaphylactic reactions (particularly in people bitten in past); intravascular envenomation
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Suggested Reading
Boustani MR et al: Babesiosis. Clin Infect Dis 22:611, 1996; Clark RF et al: Clinical presentation and treatment of
black widow spider envenomation: a review of 163 cases. Ann Emerg Med 21:782, 1992; Clark RF et al: Stingray envenomation:
a retrospective review of clinical presentation and treatment in 119 cases. J Emerg Med 33:33, 2007; Deprés-
Brummer P et al: Capnocytophaga canimorsus sepsis presenting as an acute abdomen in an asplenic patient. Neth J
Med 59:213, 2001; Fulton JA et al: Fasciotomy after envenomation: measure twice and cut once. Ann Emerg Med
45:338, 2005; Hoover NG et al: Use of antivenin to treat priapism after a black widow spider bite. Pediatrics 114:e128,
2004; Leav BA et al: Cryptosporidium species: new insights and old challenges. Clin Infect Dis 36:903, 2003; Najman
L et al: Rattlesnake envenomation. Compend Contin Educ Vet 29:166, 2007; O'Malley GF et al: Successful treatment
of latrodectism with antivenin after 90 hours. N Engl J Med 340:657, 1999; Pollock KG et al: Cryptosporidiosis and filtration
of water from Loch Lomond, Scotland. Emerg Infect Dis 14:115, 2008; Rorman E et al: Congenital toxoplasmosis--prenatal
aspects of Toxoplasma gondii infection. Reprod Toxicol 21:458, 2006; Sherman RP et al: Black widow
spider (Latrodectus mactans) envenomation in a term pregnancy. Curr Surg 57:346, 2000; Swanson DL et al: Bites of
brown recluse spiders and suspected necrotic arachnidism. N Engl J Med 352:700, 2005; Wolska-Kusnierz B et al:
Cryptosporidium infection in patients with primary immunodeficiencies. J Pediatr Gastroenterol Nutr 45:458, 2007.
Educational Objectives
| The goal of this program is to improve management of infections resulting from insect bites and animal exposures. After
hearing and assimilating this program, the clinician will be better able to:
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| 1. Describe modes of transmission and syndromes of babesiosis and toxoplasmosis.
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| 2. Select appropriate therapy for immunocompromised patients who have toxoplasmosis.
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| 3. List differences between dog bites and cat bites.
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| 4. Review regimens for tetanus and rabies prophylaxis.
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| 5. Identify and treat envenomations by black widow spiders, stingrays, and rattlesnakes.
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Faculty Disclosure
In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and members of the planning
committee to disclose relevant financial relationships within the past 12 months that might create any personal conflicts
of interest. Any identified conflicts were resolved to ensure that this educational activity promotes quality in health
care and not a proprietary business or commercial interest. For this program, the faculty and planning committee reported
nothing to disclose.
Acknowledgments
Dr. Glew spoke in Providence, RI, at Pets, People, and Pathogens: Be a Victor, Not a Vector, presented December 4, 2007,
by the Rhode Island Veterinary Medical Association and Coastal Medical, Inc. Dr. Schneir was recorded in San Diego,
CA, at the 50th Annual Postgraduate Symposium Family Medicine Update 2007, presented August 3-5, 2007, by the San
Diego Academy of Family Physicians. The Audio-Digest Foundation thanks the speakers and the sponsors for their cooperation
in the production of this program.
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