58 Bites and Arthropod-Borne Diseases

Flashcards covering animal and human bites, snake envenomation, tick-borne illnesses, and arthropod stings based on the provided lecture transcript.

What are the common sources of bacteria that contaminate bite wounds?

The environment, the skin flora of the victim, and the oral flora of the biter.

For how long is preemptive antimicrobial therapy typically recommended for acute moderate-to-severe bite injuries?

$3$ to $5\text{ days}$.

In puncture wounds or bites not considered clean and minor, when is a tetanus booster ($Td$ or $Tdap$) required?

If it has been $\geq 5\text{ years}$ since the last dose.

What is the recommended treatment for cat bites to prevent rapidly advancing infection caused by Pasteurella multocida?

Amoxicillin-clavulanate, or a combination of clindamycin with doxycycline, sulfamethoxazole-trimethoprim, or a fluoroquinolone.

What is the causative agent and vector for Cat Scratch Disease (CSD)?

Causative agent: Bartonella henselae; Vector: Contaminated flea feces (Ctemocephalides felis).

What is the primary inoculation lesion characteristic of Cat Scratch Disease?

A small painless erythematous papule or pustule that appears within days to $2\text{ weeks}$.

What is the preferred treatment for Cat Scratch Disease if significant lymphadenopathy is present?

Azithromycin for $5\text{ days}$.

What percentage of dog bites typically become infected?

$15$ to $20\%$.

Which organism from a dog bite can cause fulminant sepsis and disseminated intravascular coagulation (DIC) in asplenic or immunosuppressed hosts?

Capnocytophaga canimorsus.

Which group of snakes is characterized by having venom glands behind the eyes and hollow anterior maxillary fangs?

Viperidae and Elapidae.

What percentage of pit viper bites are considered "dry" (no venom injected)?

$20$ to $25\%$.

What field treatments should be strictly avoided for venomous snake bites?

Do not attempt to suck out the venom, do not use a tourniquet, and do not apply venom sequestration devices.

What are the standard antivenoms used for pit viper and coral snake envenomations in the United States?

Pit vipers: CroFab or Anavip; Coral snakes: Antivenin.

What condition may develop from a Russell's viper bite specifically?

Pituitary insufficiency.

Which two organisms are the primary causes of rat-bite fever in the United States?

Streptobacillus moniliformis and Spirillum minor.

What are the hallmarks of rat-bite fever after the initial wound has healed?

Fever, chills, headache, and severe migratory arthralgias followed by a maculopapular rash on the palms and soles.

What is the causative agent and common vectors for Tularemia?

Causative agent: Francisella tularensis; Vectors: Ticks (Amblyomma americanum, Dermacentor spp.) and deer flies.

When is Rabies post-exposure prophylaxis (PEP) indicated for bat encounters?

For any bite or scratch, or when direct contact occurred and a bite or scratch cannot be ruled out (e.g., a person sleeping in a room with a bat).

What is the most common wound isolate found in human bites?

Viridans streptococci (specifically Streptococcus anginosus).

Why is amoxicillin-clavulanic acid preferred over first-generation cephalosporins for human bites?

First-generation cephalosporins do not provide adequate coverage for Eikenella corrodens and common anaerobic organisms.

Where do clenched-fist injuries ("fight bites") most commonly occur?

Over the $3\text{rd}$ and $4\text{th}$ metacarpophalangeal joints.

What is the incubation period for Rocky Mountain Spotted Fever (RMSF) after inoculation by Rickettsia rickettsii?

$2$ to $14\text{ days}$.

What is the gold standard antibiotic treatment for most tick-borne rickettsial diseases including RMSF, Ehrlichiosis, and Anaplasmosis?

Doxycycline.

How is Human Granulocytotropic Anaplasmosis (HGA) often diagnosed on a peripheral-blood smear?

By observing neutrophil morulae in $20$ to $75\%$ of cases.

What is the causative agent of Lyme disease and its primary vector in the Northeast US?

Causative agent: Borrelia burgdorferi; Vector: Ixodes ticks.

What protozoan parasite causes Babesiosis and what are its severe complications?

Babesia microti; Complications include severe hemolytic anemia, ARDS, and splenic rupture.

What is the classic physical presentation of a bubonic plague infection caused by Yersinia pestis?

A bubo (an exquisitely painful, hemorrhagic, and necrotic regional lymph node).

What are the cutaneous signs of a Brown Recluse (Loxosceles reclusa) spider bite?

A central induration surrounded by a pale ischemic zone and an outer zone of erythema.

What is the mechanism of action of North American black widow venom?

$\alpha\text{-Latrotoxin}$ binds to presynaptic nerve terminals, causing the massive depletion of acetylcholine and norepinephrine.

Where does Sarcoptes scabiei var. hominis typically burrow on the human body?

Volar wrists, digital web spaces, and the belt line.