CASE STUDY
Pets & Other Animal Sentinels
A 60-year-old woman is admitted to the hospital in the Northeastern U.S. with fever, headache, nausea, vomiting, fatigue, and altered mental status. She reports that her dog died the week before – that also had fever and neurological problems.
This case will guide you through a clinical encounter to understand the patient's health challenges – and how to respond.
LEARNING OBJECTIVES
Understand three reasons why animals can be “sentinels” for environmental health hazards to humans, including infectious and non-infectious hazards related to environmental change
Explain four reasons for health care providers to communicate with veterinarians about health events
Explain five ways to communicate with veterinarians about animal health and sentinel disease events related to shared environmental risks
CLINICAL COMPETENCIES
Understand what to do when patients give history of sick animals in the house or nearby
Develop communication strategies with veterinarians and animal health experts
Recognize sentinel cases (human and animal)
Understand how to notify regarding sentinel cases as a first step to improving shared environments
A Continuing Medical Education activity presented by the Stanford Center for Innovation in Global Health and the University of Washington. View CE information and claim credit HERE.
Clinical Approach
Consider the following questions as you work through this case:
During medical encounters, patients may mention health concerns for a pet.
When this happens, consider whether there are implications for the care of the patient.
Consider communicating directly with a veterinarian about a particular issue. Human healthcare providers and veterinarians are often using similar diagnostic technology and treatments, yet often there is limited communication between the veterinary and human healthcare sectors about clinical issues.
Animals are sharing environments with humans and may be “sentinels” of environmental hazards relevant to humans as well.
History (of Human)
Taking a clinical history of your patient yields the following information:
Chief complaint
- Fever and malaise: “just like what my dog had”
History of present illness
- The patient was well until five days ago, when she developed nausea, vomiting, and fever. She was seen in an urgent care center and sent home with a clear liquid diet and a diagnosis of gastroenteritis. Since visiting urgent care, she has gotten sicker, with a worsening headache and some confusion. No rash, no sick contacts, no diarrhea.
- The patient's dog had similar clinical signs/clinical presentation and died the week before, euthanized by the veterinarian because of a “suspected brain tumor.”
- The patient is started on IV levofloxacin in Emergency Department for suspected urinary tract infection (UTI).
Past medical & surgical history
- Hypertension
Medications
- Levofloxacin for suspected UTI
- Takes ACE inhibitor for hypertension
Allergies
- No allergies
Family history
- N/A
Social & enviromental history ("Social-E")
- Widow, retired accountant
- No significant alcohol use, no drugs or tobacco
- Lives in suburban Northeastern US
- Often goes on walks with her dog
- Has seen ticks in area and has removed ticks from dog in past but not recently
Review of systems
- Generalized fatigue
- No weight change; palpitations; cough, shortness of breath; jaundice; diarrhea; joint swelling; lymphadenopathy
Discussion
What kind of follow-up should a clinician do for the chief complaint about a sick dog?
What kind of additional history would you want?
Key Questions to Ask
Asking your patient the following questions gives you this information:
What kind of animals are you in contact with?
- No other pets besides the dog previously mentioned.
- No exposures to farm animals or wildlife.
If you have pets, do they go outside?
- The dog had run freely in a wooded area in New Jersey shortly before its illness. She had to run into the woods a couple of times to call the dog back.
- Dog sleeps in the house.
Any other illness in animals nearby or concerns about animal health?
- Patient not aware of other sick dogs.
Are you and the dog exposed to any chemical hazards in the environment?
- No.
Have you or the dog had any tick bites?
- She does not recall seeing any ticks on the dog recently, although in the past she has removed ticks from the dog.
Has your veterinarian said anything about the sick dog that could be important for your health?
- Patient forgot to ask.
Physical Exam (of Human)
When you examine your patient, you learn the following:
General
- Vitals within normal limits except for fever
- Appears tired
Head Eyes Ears Nose Throat (HEENT)
- Unremarkable
Neck
- No stiffness
Chest & lungs
- Clear lungs to exam
Heart & Cardiovascular
- Tachycardic, regular, no murmur
Abdominal
- Diffuse tenderness no rebound
Musculoskeletal
- No joint swelling
Genitourinary
- No costovertebral angle (CVA) or suprapubic tenderness
Skin
- Diaphoretic
- No definite rash
Neurologic
- Appears slightly confused but able to give history.
- Strength symmetric, Deep tendon reflexes normal. No tremor.
Discussion
What additional information would be useful at this point?
Diagnostics
Information that will be helpful in diagnosing your patient:
What tests would be appropriate at this time?
Complete blood count: (CBC) with White Blood Cell Count (WBC) 3.8X109/L, platelet count 99X109/L (low), hemoglobin 12.7 g/dL
Chemistries remarkable for serum sodium 133 mmol/L (low)
Urinalysis with 1+ leukocytes, nitrite negative on dipstick
Serology sent for Lyme disease, Ehrlichia
Blood smear negative for Babesia
Chest X-ray normal
Discussion
What is the differential diagnosis for a situation where both human and dog are sick?
Fever suggests infectious cause.
Urinalysis shows some leukocytes, but this could be normal.
Differential diagnosis for the combination of a sick dog and human is broad – infectious and non-infectious causes.
Infectious causes:
Zoonotic diseases (eg. dog gives infection to human)
Bacterial:
Bartonella (more commonly from cats)
Brucellosis
Leptospirosis
Bordetella (mostly respiratory)
Campylobacter spp.
Salmonella spp.
E. coli (can also be shared food or environmental source)
Parasitic
Toxocara spp: visceral larva migrans, especially in children
Giardia, other GI pathogens
Reverse zoonotic and/or shared infectious diseases (e.g., human infects dog or both human and dog infected from a shared environment)
Bacterial
TB (human to dog)
Vector-borne
Lyme (Borellia burgdorferi)
Rocky Mountain Spotted Fever (Rickettsia rickettsii)
Other (Ehrlichioses, anaplasmosis)
West Nile virus
Viral
SARS Co-V-2
Parasitic
Toxoplasmosis
Differential Diagnosis
assessing possible diagnoses:
Non-infectious conditions affecting humans and pets:
Cancer (dogs and humans can get cancer from environmental exposures: lymphoma, mesothelioma, etc.)
Food poisoning: mycotoxin poisoning, etc.
Harmful algae blooms/toxins
Other toxic exposures: pesticides, antifreeze, poisonous plants, carbon monoxide, etc.
More information about both human patient and the animal may lead to correct diagnosis.
Also remember that animals can get sick from diseases that are not zoonotic.
With permission of the patient, you telephone the veterinarian who cared for the dog that died. The veterinarian has been trying to contact the (human) patient!
Contacting the Veterinarian
following up for more information on patient’s pet:
Dog was 9-year-old Labrador retriever.
8 days ago, the dog became lethargic and was unable to get up.
The veterinarian physical exam found ataxia and nystagmus.
Dog was treated with amoxicillin, but got worse, and the dog was admitted to an animal hospital.
On exam, animal was stuporous. Findings included:
Temp 39.5 C (normal, <39.5 C)
Scrotal erythema
Ecchymoses
Extensor rigidity of the forelimbs
Opisthotonos
History (of Pet)
more context on patient’s dog:
LP: protein 250mg/DL, cells 50X10 6/L
CT scan: Dilatation of the lateral ventricles, poorly defined region of contrast enhancement in the brainstem
Provisional diagnosis (of dog): Encephalitis or obstructive hydrocephalus secondary to a central nervous system tumor
Dog euthanized.
Necropsy findings:
Erythema and edema of the scrotum and tunica vaginalis
Extensive hemorrhages in the epididymis and testes
Focal subarachnoid hemorrhage over ventral brainstem
Veterinarian has sent tissue to CDC; is concerned about possible Rocky Mountain Spotted Fever.
Diagnostics (of Pet)
more context on patient’s dog:
Discussion
How does this information affect management?
Rocky Mountain Spotted Fever (RMSF)
Both dogs and human are susceptible to RMSF
Rocky Mountain Spotted Fever is a tick-borne rickettsial disease. The vector in the Northeastern US is the American dog tick. There is high mortality if untreated and high morbidity if treatment is delayed.
In the initial presentation of RMSF, many patients do NOT have classic triad of tick bite, fever, and rash.
In this case, sharing of information between human health and veterinarian is key to making the diagnosis.
RMSF has patchy distribution. Since dogs get severe disease as well, cases in dogs in a community can alert human health to local risk of RMSF (dogs as sentinels).
Dogs may bring ticks into house.
Removing ticks from an animal can be a major risk factor for human infection.
Suspected Diagnosis
arriving at a conclusion Based on new information from the vet:
Due to suspicion of RMSF, antibiotic is switched to Doxycycline
Serology for RMSF added to other labs
Lab contacted to see whether PCR test for RMSF is available.
Management & Treatment
You can help your patient in the following ways:
Reducing host vulnerability / susceptibility (host factors):
Educate patient on tick prevention:
Use of tick-repellent clothing (e.g., Permethrin-impregnated clothing)
Avoiding tick prone areas
Utilizing insect repellents
Checking clothing, pets, and gear after exposure
Taking shower soon after exposure
Checking body for ticks (see graphic)
Optimize medical status, immunocompromising conditions
Reducing exposures / improving environments (environmental factors):
Tick control collar or other treatment for pets
Landscape modification to reduce tick exposures
Prevention
How can Rocky mountain spotted fever be prevented?
Beyond the Clinic
Your patient's story is part of a bigger picture:
Global and local environmental change is affecting the health of non-human animals as well as humans. Species extinction and loss of biodiversity is a major consequence of global environmental change. While emerging zoonotic diseases are one obvious shared risk between animals and humans, exposures to toxic chemicals and climate change related effects often affect animals before humans.
Greater awareness of environmental effects on non-human animals could improve understanding of human risk. Many emerging infectious diseases make animals sick as well. Therefore, clinicians should be prepared to communicate with veterinarians when there are reports of sick or dead animals.
Globally, there is increasing recognition of the importance of the “One Health” concept, considering the health of humans, animals, and their shared environment, and stressing interprofessional collaboration between medical providers, veterinarians, and environmental health experts. For example, there has been a recent “quadripartite” agreement between the WHO, the World Organization for Animal Health (WOAH), the UN Food and Agriculture Organization (FAO), and the United Nations Environmental Program (UNEP) in support of One Health approaches to health system strengthening.
Case Follow Up
What happens next:
The patient improves after starting the doxycycline.
Stool, urine, blood cultures negative
Serology for Lyme, Ehrlichia, Anaplasma negative
Acute and convalescent sera for RMSF:
Day 17: IgM 1: 1,024, IgG 1:512
Day 89 IgM 1: 256, IgG 1:256
Results of biopsy on dog brain and testes tissue (sent to CDC).
Abundant spotted fever group rickettsial antigen, consistent with Rocky Mountain Spotted Fever
Call to Action
Clinicians can take action to advance planetary health:
At the clinic:
History taking: should include questions about animal contact and recent animal illness/health issues.
Develop protocols for communication between human health care providers and local veterinarians about individual patients.
Educate patients about environmental health risks affecting both their pets and themselves, and encourage them to seek veterinary care if concerns about animal health.
Educate patients to reduce tick exposure for themselves and pets.
In your community:
Get to know the veterinarians in your community and start building interprofessional relationships with them. Discuss possibilities for interprofessional collaboration on cases.
Work with the local public health agencies to improve communication and coordination between local veterinarians and human health clinicians.
Collaborate with veterinarians in your community about addressing local environmental health problems affecting both animals and people.
At the societal level:
Collaborate with veterinarians and other professionals to raise concerns about emerging infectious diseases, climate change, pollution, biodiversity loss, and other shared health risks.
Summary and
Key Learning Points
also available for download here:
Reasons for healthcare providers to communicate with veterinarians include:
Global and local environmental change is affecting both humans and non-human animals.
Animals may pose zoonotic disease risk to patient; however animals get sick from many zoonotic diseases as well.
Veterinarians receive more training than human health care professionals in zoonotic disease, but training is focused on disease in animals and risk mitigation.
Animals may be more sensitive than humans to the effects of chemical pollution and other environmental hazards. Animals may therefore be “sentinels” of environmental change and health hazards relevant to humans, since there are usually shared environmental risks (eg. humans and animals sharing environments in close contact).
The human-animal bond is important. Since animals are considered “part of the family,” their health and healthcare may be prioritized.
Domesticated animals (and wildlife) are receiving increasingly sophisticated veterinary care, including diagnostics and imaging and treatments that are similar to those in human healthcare.
There is potential for medication errors and abuse between human and animal prescriptions.
Opportunities for interprofessional practice: human health and veterinarians:
Develop protocols for regular communication between local veterinarians and human health clinicians.
Develop regular meetings between human healthcare providers and veterinarians in a community.
Contact veterinarian directly (telephone, email, etc.) with permission of patient.
Request records release (with patient permission).
Ask patients to convey message to their veterinarian.
Contact your public health department to contact animal health officials.
Additional Resources
CDC One Health: https://www.cdc.gov/onehealth/index.html
WHO One Health Joint Plan of Action: https://www.who.int/news/item/17-10-2022-one-health-joint-plan-of-action-launched-to-address-health-threats-to-humans--animals--plants-and-environment
Arbonet Disease Maps – Vector-borne disease cases in humans, animals, and vectors: https://wwwn.cdc.gov/arbonet/maps/ADB_Diseases_Map/index.html
CDC tick prevention: https://www.cdc.gov/ticks/avoid/on_people.html
References
Bischoff K, Priest H, Mount-Long A. Animals as sentinels for human lead exposure: a case report. J Med Toxicol. 2010 Jun;6(2):185-9. doi: 10.1007/s13181-010-0014-9. PMID: 20238198; PMCID: PMC3550297.
Gilbert L. The Impacts of Climate Change on Ticks and Tick-Borne Disease Risk. Annu Rev Entomol. 2021 Jan 7;66:373-388. doi: 10.1146/annurev-ento-052720-094533. PMID: 33417823.
Paddock CD, Brenner O, Vaid C, Boyd DB, Berg JM, Joseph RJ, Zaki SR, Childs JE. Short report: concurrent Rocky Mountain spotted fever in a dog and its owner. Am J Trop Med Hyg. 2002 Feb;66(2):197-9.
Rabinowitz P, Scotch M, Conti L. Human and animal sentinels for shared health risks. Vet Ital. 2009 Jan-Mar;45(1):23-4.
Steele SG, Booy R, Manocha R, Mor SM, Toribio JLML. Towards One Health clinical management of zoonoses: A parallel survey of Australian general medical practitioners and veterinarians. Zoonoses Public Health. 2021 Mar;68(2):88-102. doi: 10.1111/zph.12799. Epub 2020 Dec 31. PMID: 33382160; PMCID: PMC7986233.
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