When patients present with symptoms of pet-related diseases, you may not at first connect their clinical features of infection or allergy with their pet — be it cat, dog, bird, or something more exotic. But it is important to know the signs of disease that may point to animal causes, as this may drastically change your approach to the patient’s care.

Do you know the pet-related diseases you’ll find walking through your office or hospital door? Quiz yourself with the following 6 sample questions from NEJM Knowledge+.

Question 1

A 32-year-old woman reports a 2-week history of swelling behind her left ear. She does not have any systemic symptoms and has not noticed swelling elsewhere on her body. She recently lost about 2.3 kg and currently smokes. She states that she has not engaged in recent high-risk sexual behavior. She has a newly acquired kitten, who recently scratched her, and she keeps an aquarium. She has no known exposure to tuberculosis.

Examination reveals a red, tender, retroauricular fluctuant lymph node measuring 2 cm by 2 cm behind her left earlobe (figure). No other lymph nodes are enlarged.

Which one of the following next steps is most appropriate in managing this patient’s lymphadenopathy?

  1. Perform excisional biopsy of the lymph node; send tissue for pathological examination
  2. Administer an interferon-gamma release assay
  3. Perform incision and drainage of the lymph node in the office; send material for wound culture
  4. Aspirate the lymph node; send material for acid-fast bacilli culture
  5. Perform serologic testing for Bartonella henselae

Question 2

An 8-year-old boy is brought to the emergency department (ED) by his parents one hour after an unknown dog bit him in the right lower leg. An animal control form was completed in triage.

His medical history is unremarkable, except for an episode of rash and difficulty breathing that occurred when he received amoxicillin a few years ago. He is up-to-date with his immunizations, having received his last set before entering kindergarten at age 5 years.

His vital signs are stable, and he appears well. He has a 10-cm semicircular laceration on the right lower leg and several puncture wounds beneath it. There is no surrounding erythema, warmth, or drainage. No tissue is missing or devitalized, but the wound is large enough to require suturing.

What is the most appropriate antimicrobial management for this patient?

  1. Amoxicillin–clavulanate
  2. Amoxicillin only
  3. Clindamycin only
  4. Trimethoprim–sulfamethoxazole plus clindamycin
  5. Trimethoprim–sulfamethoxazole only

Question 3

A 48-year-old man is concerned about a dog bite he received 6 days ago while he was jogging during a visit to Mexico. He states that he tried to shoo the dog away, but it ran up to him and bit his leg. He has never previously received rabies vaccination. He has no other medical conditions.

Physical examination reveals a superficial, clean wound on his right calf that is healing well.

Which one of the following steps is most appropriate for managing this patient’s dog bite?

  1. Infiltrate the right calf with rabies immunoglobulin; initiate postexposure rabies vaccination
  2. Infiltrate the wound with rabies immunoglobulin
  3. No rabies prophylaxis is necessary; treat the wound with amoxicillin–clavulanate
  4. Initiate postexposure rabies vaccination
  5. No rabies prophylaxis or antibiotic treatment is indicated at this time

Question 4

A 65-year-old woman is referred for evaluation of a nagging, nonproductive cough and an abnormal chest radiograph (figure). She says that the cough started 1 to 2 years ago but has worsened in the past 6 months, has become associated with dyspnea on exertion, and is limiting her ability to continue her job as a tour guide. She also reports 25 pounds of unintended weight loss in the past 5 months. She states that she does not experience fevers, chills, or hemoptysis, and that she does not smoke or use illicit drugs. Until recently, she had numerous birds, including parakeets, in her home.

Physical examination reveals tachypnea and crackles at the bases of both lungs. Her oxygen saturation is 87% while she is breathing ambient air and drops to 82% with ambulation. A bronchoalveolar lavage reveals 70% lymphocytes. Removing the birds from the patient’s home has minimally improved her cough, but her dyspnea and desaturation with ambulation persist.

In addition to administration of supplemental oxygen, which one of the following pharmacologic treatments is most appropriate for this patient?

  1. Oral prednisone
  2. Infliximab
  3. Amoxicillin–clavulanate
  4. N-acetylcysteine
  5. Azathioprine

Question 5

A 5-year-old boy is brought in for evaluation of a “round red spot” on his right middle finger. His father reports that the lesion began as a small, pruritic red circle that spread outward. He reports that his older son, who is on the high school wrestling team, once had a similar rash.

Examination of the patient’s right middle finger reveals a 3-cm, well-circumscribed, scaly erythematous oval patch (figure 1 and figure 2).

Which one of the following treatments is most appropriate for this patient?

  1. Topical 0.05% clobetasol twice daily
  2. Topical clotrimazole twice daily
  3. Topical 1% hydrocortisone twice daily
  4. Topical nystatin twice daily
  5. Topical mupirocin twice daily

Question 6

A 46-year-old woman reports a 3-day history of decreased vision in her right eye. She notes photophobia and eye pain but denies trauma. She has rheumatoid arthritis and was started on immunosuppressive therapy with adalimumab 2 months ago.

On examination, there is no conjunctival injection; her visual acuity is 20/100 in her right eye and 20/30 in her left eye. Funduscopic evaluation reveals significant vitreous inflammation and an area of fluffy white necrotizing retinitis adjacent to a pigmented chorioretinal scar (figure).

Which one of the following infectious etiologies is the most likely cause of this patient’s vision loss?

  1. Cytomegalovirus
  2. Adenovirus
  3. Toxoplasma gondii
  4. Bartonella henselae
  5. Streptococcus pneumoniae

What Animal-Related Illnesses Have You Encountered in Your Practice?

Physicians often encounter mystery ailments and might not immediately think “animal related.” But they are likely more common than you might assume. According to the 2012 U.S. Pet Ownership & Demographics Sourcebook, 36.5% of households in the United States own dogs, 30.4% own cats, 3.1% own birds, and 1.5% own horses. In addition, 35,670 people work on farms dealing with cattle, sheep, swine, goats, horses, chickens, fish, shellfish, and bees — according to the U.S. Department of Labor. So NEJM Knowledge+ includes a few questions about farmworkers’ ailments as well. (In fact, our question banks of thousands of case-based questions are easy to search to find specific learning objectives on many of the topics you need to know to keep up with medical knowledge in internal medicine, family medicine, and pediatrics.)

As the American Family Physician writes, “The clinical history in the primary care office should routinely include questions about pets and occupational or other exposure to pet animals.”

Have you run into your fair share of pet-related diseases? Learned something from the case-based questions we’ve offered above? Share your stories in the comments below.

  • More on NEJM Knowledge+ Content:

    Roadmap to Great Content

    Work Less and Learn More: Here’s How in NEJM Knowledge+

    Content Updates