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+.
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.
Which one of the following next steps is most appropriate in managing this patient’s lymphadenopathy?
- Perform excisional biopsy of the lymph node; send tissue for pathological examination
- Administer an interferon-gamma release assay
- Perform incision and drainage of the lymph node in the office; send material for wound culture
- Aspirate the lymph node; send material for acid-fast bacilli culture
- Perform serologic testing for Bartonella henselae
E. Perform serologic testing for Bartonella henselae
Key Learning Point:
Lymphadenitis in a patient with a recent scratch from a kitten suggests a diagnosis of cat scratch disease due to Bartonella henselae.
Lymphadenitis in a patient with a recent scratch from a kitten suggests cat scratch disease from Bartonella henselae. This infection usually begins with a primary cutaneous papule or pustule approximately 3 to 10 days after animal contact. Most commonly, regional lymphadenopathy develops ipsilateral to the inoculation site (mainly head, neck, or upper extremity). There may be overlying erythema and, in 10% to 15% of cases, the lymph nodes may suppurate. Nearly half of patients with cat scratch disease have single lymph node involvement, 20% have multiple node involvement at one site, and the remaining one-third have node involvement at multiple sites. The diagnosis is confirmed with serologic testing.
In cat scratch disease, the lymphadenopathy will resolve on its own. If the lymph node persists or if the presentation is atypical, further diagnostic testing, such as aspiration or excisional biopsy, should be pursued.
Incision and drainage is generally used to treat skin and soft-tissue abscesses; it is not required if the lymphadenitis is due to Bartonella.
Interferon-gamma release assays are done to diagnose latent tuberculosis infection; in this case, that diagnosis is less likely than cat scratch disease because the patient had no known exposure to tuberculosis.
Last reviewed Dec 2016. Last modified Jul 2014.
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?
- Amoxicillin only
- Clindamycin only
- Trimethoprim–sulfamethoxazole plus clindamycin
- Trimethoprim–sulfamethoxazole only
D. Trimethoprim–sulfamethoxazole plus clindamycin
Key Learning Point:
Antimicrobial management of an animal bite should treat the following bacterial pathogens: Pasteurella species, Staphylococcus species, Streptococcus species, and Capnocytophaga canimorsus.
The most frequent complications of animal bites are infections. The risk of developing an infection and the severity of the infection are related to the type of animal, the location of the bite, the size of the wound, and the need to close the wound surgically. Bite wounds usually result in polymicrobial infections, with aerobic and anaerobic bacteria that come mainly from the animal’s oral flora but also from the child’s skin and surrounding environment.
Pasteurella, Staphylococcus, and Streptococcus species, in addition to Capnocytophaga canimorsus, are the most common causes of infections from dog and cat bites. Eikenella corrodens is a common cause of infection from human bites.
The general management for bite wounds is no different from what is usually recommended for other wounds. The site of the bite should first be vigorously washed with soap and water to reduce the bacterial inoculum, and any devitalized tissues should be debrided. There is still debate about whether clinically uninfected wounds should be sutured immediately or left open for 24 hours to permit evaluation for possible development of infection. However, delayed closure must be considered when a bite involves the head, hands, or feet; when a significant crush injury has occurred; or when there are clear signs of edema.
Antibiotic treatment is indicated for animal-bite wounds that are at high risk for infection. These include skin-puncture wounds, wounds that require suturing (as in this case), and wounds that puncture joint or bone.
When empiric therapy is indicated, amoxicillin–clavulanate is the recommended first-line treatment because this combination is active against most of the pathogens that can be isolated from bite wounds. For patients who are allergic to penicillin (as in this case), the combination of clindamycin and either trimethoprim–sulfamethoxazole or an extended-spectrum cephalosporin is a reasonable option to adequately cover likely pathogens.
Penicillin and ampicillin are effective against Pasteurella species, but they should not be used alone without a beta-lactamase inhibitor, such as clavulanate, because Staphylococcus species and most of the anaerobic bacilli that may cause infections produce beta-lactamase. In more-severe cases, or if a patient is unable to take oral antibiotics, intravenous ampicillin–sulbactam can be considered.
A tetanus toxoid booster, together with human tetanus immune globulin, is recommended for children who have received fewer than three doses of the vaccine. Tetanus prophylaxis is not necessary for adequately vaccinated children unless the wound is dirty and the last tetanus dose was given 5 or more years ago,in which case a booster dose is recommended. When tetanus prophylaxis is indicated, it should be administered as soon as possible after a wound, even in patients who present late for medical attention.
In addition to providing antibiotic prophylaxis and assessing the need for tetanus prophylaxis, all animal bites should be evaluated for rabies risk. Local health departments can provide consultation about specific cases and give recommendations regarding the need for postexposure prophylaxis depending on the animal involved, the circumstances surrounding the bite, and the local epidemiology.
Last reviewed Dec 2016. Last modified July 2016.
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?
- Infiltrate the right calf with rabies immunoglobulin; initiate postexposure rabies vaccination
- Infiltrate the wound with rabies immunoglobulin
- No rabies prophylaxis is necessary; treat the wound with amoxicillin–clavulanate
- Initiate postexposure rabies vaccination
- No rabies prophylaxis or antibiotic treatment is indicated at this time
A. Infiltrate the right calf with rabies immunoglobulin; initiate postexposure rabies vaccination
Key Learning Point:
A person who is bitten by an animal that is at high risk for rabies should be managed with postexposure vaccination and administration of immunoglobulin.
Rabies infection from domestic dogs in the United States is exceedingly rare and is more likely to occur from exposure to bats, skunks, or raccoons. However, globally (including in Mexico), dogs are the major reservoirs of the rabies virus. Exposure to rabies, a Lyssavirus, occurs when the skin is penetrated by teeth or when a person has direct transdermal or mucosal contact with infectious material, such as brain tissue or saliva from an infected animal.
Patients with a high-risk exposure to rabies, such as a dog bite that occurred in Mexico and punctured the skin, should receive postexposure prophylaxis consisting of three primary elements:
- Wound care.
- Administration of rabies immunoglobulin. When the wound is visible, as much of the dose as is feasible should be infiltrated directly in and around the wound.
- Administration of rabies vaccine.
Immunocompetent patients who have not been previously vaccinated should receive four doses of vaccine on days 0, 3, 7, and 14 — in addition to a single dose of rabies immunoglobulin on day 0. People who have previously received a vaccine series do not require immunoglobulin and should receive two doses of the vaccine on days 0 and 3.
If the wound is superficial and healing well, it does not require treatment with antibiotics.
Last reviewed May 2016. Last modified Jul 2014.
- Rupprecht CE and Gibbons RV. Clinical practice. Prophylaxis against rabies. N Engl J Med 2004 Dec 17; 351:2626.
- Use of a reduced (4-dose) vaccine schedule for postexposure prophylaxis to prevent human rabies: recommendations of the advisory committee on immunization practices. MMWR Recomm Rep 2010 Mar 20; 59:1.
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?
- Oral prednisone
A. Oral prednisone
Key Learning Point:
The most appropriate initial pharmacologic therapy for a patient with hypersensitivity pneumonitis is a systemic glucocorticoid.
Hypersensitivity pneumonitis (HP) is an interstitial lung condition characterized by inflammation in response to the inhalation of organic antigens to which the patient has been previously sensitized. Bronchoalveolar lavage frequently reveals a lymphocytic predominance but is not a sensitive diagnostic test. Chest imaging can reveal evidence of fibrosis.
Bird antigens are known to cause HP specifically known as “bird fancier’s lung.” The most important intervention is to remove the offending exposure. For patients with symptomatic, progressive disease, initial therapy includes prednisone 0.5 to 1.0 mg per kilogram of ideal body weight, tapered slowly to a maximum of 60 mg daily.
Amoxicillin–clavulanate is not itself a therapy for HP.
Although infliximab and azathioprine are used to treat autoimmune diseases, they are not first-line therapy for HP.
Indirect evidence supports the use of N-acetylcysteine in patients with HP, but it is not a first-line therapy.
Last reviewed Jun 2016. Last modified Apr 2014.
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.
Which one of the following treatments is most appropriate for this patient?
- Topical 0.05% clobetasol twice daily
- Topical clotrimazole twice daily
- Topical 1% hydrocortisone twice daily
- Topical nystatin twice daily
- Topical mupirocin twice daily
B. Topical clotrimazole twice daily
Key Learning Point:
The appropriate first-line therapy for tinea corporis is a topical azole antifungal, such as topical clotrimazole, twice daily.
Tinea corporis, or “ringworm,” is a cutaneous dermatophyte infection usually associated with Trichophyton tonsurans or Trichophyton rubrum, which can be found in soil, on humans, and on animals. Isolated lesions need not raise concern about immunocompetence and are common among children in homes with infected animals and among children who play sports involving significant skin-to-skin contact (e.g., wrestling). Lesions are classically erythematous and annular in nature, with central clearing and a layer of scale at the edges.
Diagnosis of tinea corporis should be confirmed by visualizing hyphae using a potassium hydroxide (KOH) preparation or with growth of dermatophyte species on fungal culture.
First-line therapy for isolated tinea corporis lesions on non–hair-bearing sites is a topical azole antifungal, such as topical clotrimazole, twice daily for at least one month and continued until the lesion resolves. Oral formulations such as fluconazole, terbinafine, and itraconazole all are effective against tinea corporis but are rarely indicated for first-line use unless the condition is very widespread or involves hair-bearing sites.
Topical nystatin is ineffective against dermatophyte infections, as are antibacterial agents such as mupirocin.
Granuloma annulare is an inflammatory plaque that can be similar in shape to tinea corporis (round/annular) but lacks the characteristic scale of tinea. Although granuloma annulare is usually self-limited, persistent lesions may be treated with a high-potency topical glucocorticoid (e.g., clobetasol). Low-potency topical glucocorticoids (e.g., hydrocortisone) are often ineffective in managing granuloma annulare.
Last reviewed Dec 2016. Last modified Feb 2015.
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?
- Toxoplasma gondii
- Bartonella henselae
- Streptococcus pneumoniae
C. Toxoplasma gondii
Key Learning Point:
The most likely infectious cause of vision loss in an immunosuppressed patient with vitreous inflammation and necrotizing retinitis adjacent to a retinal scar is Toxoplasma gondii.
Ocular toxoplasmosis from Toxoplasma gondii infection may be acquired congenitally while in utero or acutely via ingestion of raw or undercooked meats or oocysts from cats. Primary infection in children and adults usually results in retinochoroidal scars and may be subclinical. Reactivation of the disease occurs at the edge of the scar and may be elicited by immunosuppression, such as in patients treated with corticosteroids or immunomodulators. The classic sign of ocular toxoplasmosis is a nidus of fluffy white necrotizing retinitis that is adjacent to a pigmented chorioretinal scar. Vitreous inflammation is also common.
Adenovirus and Streptococcus pneumoniae are typical causes of viral or bacterial conjunctivitis, but they do not cause necrotizing retinitis.
Bartonella henselae infection manifests with optic disc edema and a sunburst pattern around the macula (“macular star”).
Cytomegalovirus retinitis usually causes painless loss of vision with fluffy white retinal infiltrates, but no significant vitreous inflammation.
Last reviewed Apr 2016. Last modified Apr 2016.
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.