Tularemia From Veterinary Occupational Exposure

Abstract

Tularemia is a disease caused by Francisella tularensis, a highly infectious bacteria that can be transmitted to humans by direct contact with infected animals. Because of the potential for zoonotic transmission of F. tularensis, veterinary occupational risk is a concern. Here, we report on a human case of tularemia in a veterinarian after an accidental needlestick injury during abscess drainage in a sick dog. The veterinarian developed ulceroglandular tularemia requiring hospitalization but fully recovered after abscess drainage and a course of effective antibiotics. To systematically assess veterinary occupational transmission risk of F. tularensis, we conducted a survey of veterinary clinical staff after occupational exposure to animals with confirmed tularemia. We defined a high-risk exposure as direct contact to the infected animal’s body fluids or potential aerosol inhalation without use of standard personal protective equipment (PPE). Survey data included information on 20 veterinary occupational exposures to animals with F. tularensis in 4 states. Veterinarians were the clinical staff most often exposed (40%), followed by veterinarian technicians and assistants (30% and 20%, respectively). Exposures to infected cats were most common (80%). Standard PPE was not used during 80% of exposures; a total of 7 exposures were categorized as high risk. Transmission of F. tularensis in the veterinary clinical setting is possible but overall risk is likely low. Veterinary clinical staff should use standard PPE and employ environmental precautions when handling sick animals to minimize risk of tularemia and other zoonotic infections; postexposure prophylaxis should be considered after high-risk exposures to animals with suspected or confirmed F. tularensis infection to prevent tularemia.

Tularemia is a disease caused by infection with Francisella tularensis, a fastidious, aerobic, gram-negative coccobacillus that is highly infectious [1]. Clinical manifestation can vary depending on the exposure route; direct contact typically results in ulceroglandular or glandular presentations while inhalation of infectious aerosols typically results in pneumonic disease [1]. As a disease of public health concern, human cases of tularemia are nationally reportable; in the United States, during 2010–2020, an average of 205 cases of tularemia were reported annually [2]. Tularemia can infect many mammalian species; however, animal cases of tularemia are not nationally reportable and the incidence among animals in the United States is not known.

Transmission of F. tularensis to humans typically occurs after bites from infected arthropods [3, 4], direct contact with infected animals [5, 6], ingestion of contaminated water [7, 8] or food [9], or inhalation of contaminated aerosols [10, 11]. Transmission has also been reported in the laboratory setting [12]; most cases of laboratory-associated transmission have been reported in settings of suboptimal environmental or work controls, such as handling bacterial isolates outside a biological safety cabinet.

Because of the potential for zoonotic transmission of F. tularensis, veterinary occupational risk is a concern. Domestic cats are particularly susceptible to tularemia and transmission to humans can occur through their bite or scratch [13, 14]. Transmission has also been described from pet dogs [15–17], pet hamsters [18], pet rabbits [19–21], and pet prairie dogs [22]. After a known or suspected exposure to F. tularensis, options include close fever watch during the 14-day incubation period with initiation of treatment at fever onset, or postexposure prophylaxis (PEP) with a short course of doxycycline or a fluoroquinolone [23]. However, formal guidelines from veterinary organizations or public health agencies regarding who should be recommended for fever watch or PEP are not currently available due to limited data on transmission risk in the veterinary clinical setting.

In this report, we describe a case of veterinary occupational transmission of F. tularensis and present results of a survey of veterinary staff after occupational exposure to animals with confirmed F. tularensis infection.

CASE DESCRIPTION

A 4-pound chihuahua, housed with 5 other dogs without symptoms, was brought to a veterinary clinic in November 2021 for lethargy and vomiting. The pet owner was not aware of any known infection risk exposures, such as to other sick or dead animals. A veterinarian evaluated the dog and prescribed anti-emetic and analgesic medications. Six days later, the dog owner called the clinic to report that 2 firm swellings had developed under the dog’s jaw; a course of amoxicillin-clavulanic acid was prescribed and administered. Two days later, approximately 8 days after initial symptom onset, the dog owner noticed spontaneous drainage from the lesion and brought the dog back to the clinic. The same veterinarian examined the dog and identified a bi-lobal abscess on the neck with central necrosis. After draining the abscess by fine-needle aspiration, the veterinarian accidentally punctured her left thumb with the dirty needle. Immediately after the injury, she washed the needle puncture site with soap and water and applied topical chlorhexidine; she did not receive PEP with antibiotics. No personal protective equipment (PPE), including gloves, gown, and facial mask, was worn during the clinical evaluation and procedure. A drop of purulent fluid from the drained abscess was viewed under the microscope in the clinic laboratory, which showed many bacteria and white blood cells. The purulent exudate was placed in a sterile tube with no media, refrigerated, and sent on ice to an external laboratory for 48-hour bacterial culture. Bacterial culture was negative, molecular testing was not performed, and the specimen was discarded. After this clinical encounter, the dog was lost to follow-up; the clinical outcome is not known.

Four days after the needlestick injury, the veterinarian developed malaise, body aches, chills, and fever to 102.5°F. The following day, she developed new and rapidly enlarging painful left axillary lymphadenopathy that made it difficult for her to move her left arm; she presented to a clinic for evaluation. Other than the needlestick injury, she denied recent infectious exposure risks, including recent animal, insect, or tick bites; animal scratches; or handling wildlife. During the initial clinic encounter, an infectious disease physician was consulted who recommended obtaining blood cultures prior to direct admission to the hospital. The empirical intravenous antibiotics vancomycin and piperacillin-tazobactam were administered upon hospital admission. Laboratory testing revealed normal white blood cell count (8100 cells/mL), lactate, liver enzymes, and renal function; C-reactive protein (2.9 mg/dL) was moderately elevated. On day 2 of hospital admission, her temperature increased to 104.1°F and the pain in her left arm and axillary region worsened. Physical examination revealed left axillary and bilateral postauricular lymphadenopathy as well as 3 small tender erythematous lesions on the left anterior forearm. Laboratory testing revealed moderate elevation of liver enzymes (alanine transaminase, 100 U/L; aspartate aminotransferase, 64 U/L). An ultrasound identified multiple enlarged lymph nodes in the left axillary region without discrete abscesses. On hospital day 3, the patient noticed a small pustule developing at the location of the prior needlestick injury. Aspiration of the lesion was performed, and the fluid was sent for bacterial culture; antibiotics were changed to intravenous ampicillin/sulbactam and doxycycline to empirically cover for suspected tularemia. On hospital day 4, 10 days after the initial needlestick injury, the wound specimen was identified as F. tularensis, which was later confirmed by culture. Blood cultures remained negative. A diagnosis of ulceroglandular tularemia was made and the patient was discharged from the hospital after 4 days and completed a 21-day course of oral doxycycline 100 mg twice daily, with full resolution of symptoms including healing of the left thumb lesion (Figure 1).

Figure 1.

Left, Small pustule on the left thumb at the site of the needlestick injury, on the day of hospital discharge, after drainage. Right, Healing left thumb lesion after 1 week of doxycycline.

METHODS

After receiving the above report of the veterinarian who developed tularemia after an exposure in the veterinary clinical setting, the Centers for Disease Control and Prevention (CDC) developed a survey for veterinary staff after occupational exposure to animals with F. tularensis infection. The goals of this survey were to identify and describe veterinary staff occupational exposures to animals with F. tularensis infection, assess PPE used by veterinary staff during these exposures, evaluate the frequency of fever watch or antimicrobial PEP after exposures, and describe the clinical outcomes of exposed veterinary staff. The survey also included questions about the demographics and occupation of the exposed veterinary staff.

In early 2022, the CDC invited state public health departments to complete the survey with information obtained during past or future investigations after animals evaluated at veterinary clinics were confirmed to have tularemia. Participating health departments entered the data into a standardized form and shared results with the CDC for analysis.

Descriptive statistical analyses summarizing veterinary staff demographics, occupation, state of practice, and exposure characteristics were performed using Microsoft Excel (Microsoft Corporation). For this analysis, a high-risk exposure to F. tularensis was defined as exposure to the infected animal’s body fluids or potential aerosol inhalation, such as during procedures including necropsy, abscess drainage, or fine-needle aspiration, without standard PPE. We defined standard PPE according to the Compendium of Veterinary Standard Precautions for Zoonotic Disease Prevention in Veterinary Personnel, which recommends the use of surgical gloves and other protective outerwear (such as gowns or aprons) when handling sick or injured animals or their specimens; gloves, outerwear, and facial protection when abscesses are lanced and wounds are lavaged; and gloves, outerwear, and facial, eye, and respiratory protection during necropsy [24]. Direct exposures such as animal bites, scratches, or needlestick injuries were also classified as high-risk exposures, regardless of PPE use. Low-risk exposures included other interactions with the infected animal, such as restraining the animal, performing a physical examination, or performing procedures with standard PPE.

This study was reviewed in accordance with policies and procedures of the CDC and was determined to be exempt from Institutional Review Board requirements.

RESULTS

Surveys were completed by public health departments in 4 states (Wyoming [65%], Oklahoma [20%], North Dakota [10%], and Minnesota [5%]) and described 20 unique veterinary occupational exposures to F. tularensis–infected animals (Table 1). The Wyoming Department of Public Health had conducted a similar survey during 2016–2017 of veterinary staff after exposure to animals with confirmed tularemia and included data collected from that prior investigation.

Table 1.

Characteristics of Veterinary Staff With Occupational Exposure to Francisella tularensis–Infected Animals

	Veterinary Staff and Exposure Characteristics (N = 20)
Age (n = 18a)
19–30 y	6 (33%)
31–40 y	6 (33%)
>40 y	6 (33%)
Female	17 (85%)
State of veterinary practice
Wyoming	13 (65%)
Oklahoma	4 (20%)
North Dakota	2 (10%)
Minnesota	1 (5%)
Occupation
Veterinarian	8 (40%)
Veterinarian technician	6 (30%)
Veterinarian assistant	4 (20%)
Office administrator	2 (10%)
Animal exposure
Cat	16 (80%)
Dog	4 (20%)
Year of exposure (n = 19b)
2012	2 (10%)
2015	1 (5%)
2016	1 (5%)
2017	5 (26%)
2021	2 (10%)
2022	6 (32%)
High-risk exposurec	7 (35%)
Lack of standard PPEd	16 (80%)
Fever watch after exposure	6 (30%)
Postexposure prophylaxis	7 (35%)

Data are presented as n (%).

Abbreviation: PPE, personal protective equipment.

^aAge was not reported by 2 participants.

^bYear was not reported in 1 case.

^cA high-risk exposure was defined as direct contact to infected animal body fluids or potential aerosol inhalation without use of standard PPE.

^dStandard PPE includes use of surgical gloves and other protective outerwear (such as gowns or aprons) when handling sick or injured animals or their specimens; use of gloves, outerwear, and facial protection when abscesses are lanced and wounds are lavaged; and use of gloves, outerwear, and facial, eye, and respiratory protection during necropsy [24].

Exposures occurred during 2012–2022. Most exposed veterinary staff were female (85%) and 40 years of age or younger (66%). The most common occupation was veterinarian (40%); other occupations were veterinary technicians, veterinary assistants, and clinic office administrators.

Over three-quarters of exposures were to infected cats (80%); the rest were to infected dogs. Approximately one-third (35%) of exposures were categorized as high risk. No veterinary staff reported an exposure from an animal bite, scratch, or needlestick injury. Lack of standard PPE use was common, reported in 80% of exposures. After exposure, fever watch or PEP was used by 30% and 35% of exposed staff, respectively. Among the 7 veterinary staff who used PEP, 4 (57%) received 14 days of doxycycline and 3 (43%) received 14 days of ciprofloxacin. Notably, of the 7 veterinary staff with a high-risk exposure, fever watch was used by 5 (71%) and PEP was not used by any.

No veterinary staff reported fever or other symptoms characteristic of tularemia in the 14 days following exposure. Two veterinary staff with low-risk exposures underwent serologic testing for F. tularensis; one had negative results and one had indeterminate titers that did not increase in a serum specimen collected several weeks later.

DISCUSSION

In this report, we summarize a case of human tularemia after veterinary occupational exposure from a needlestick injury during abscess drainage of an infected domestic dog. Survey findings of 20 other veterinary staff after occupational exposure to F. tularensis did not identify other instances of transmission. Our finding of low risk of transmission of F. tularensis in the veterinary setting is consistent with another report that found no evidence of transmission when medical personnel treated humans with confirmed F. tularensis infection [25].

The CDC recommends PEP after high-risk occupational laboratory exposures to F. tularensis, typically a 2-week course of either oral doxycycline or oral ciprofloxacin, while after low-risk exposures, fever watch for 14 days is considered to be reasonable [23]. Paradoxically, we found in our survey that PEP to prevent tularemia was more often prescribed after low-risk exposures, such as when standard PPE was used appropriately or when interactions with the infected animal were limited to restraining or petting the animal. This finding may be because veterinary staff who use precautions such as standard PPE may also be more likely to use other measures to minimize the risk of infection, including PEP.

A notable limitation of PEP is that it is typically prescribed only after a recognized exposure to a particular pathogen. In the case highlighted in this report, occupational transmission of F. tularensis occurred after exposure to a sick dog that was never suspected or confirmed to have tularemia. Veterinary staff should have a high clinical index of suspicion for tularemia when an animal presents with fever and lymphadenopathy, particularly in the context of a recent exposure such as handling or killing wildlife, and consider PEP after high-risk exposures.

In the human case of tularemia described in this report, the diagnosis was made after F. tularensis was detected in the fluid from the thumb abscess; blood cultures were negative despite serious systemic signs and diffuse lymphadenopathy. If tularemia is suspected, the laboratory should be notified, samples should be plated on cysteine-containing media such as chocolate agar, and blood cultures should be held for prolonged periods [26]. Even when optimal culture conditions are used, due to the fastidious nature of F. tularensis, it is not uncommon for routine cultures to be negative, emphasizing the importance of performing molecular diagnostic testing when possible.

Despite the finding that transmissibility of F. tularensis in veterinary practice seems to be generally low, the relatively high frequency of exposure highlights the importance of routine use of standard PPE by veterinary staff. The low reported use of standard PPE by the veterinary staff in this survey highlights a key opportunity to reduce occupational zoonotic disease transmission risk not limited to F. tularensis. Even more importantly, the use of engineering, work practice, and environmental controls should be employed in the veterinary clinical setting to minimize the risk of animal interactions that might result in accidental or unnecessary zoonotic exposures [24].

This report is subject to at least 2 limitations. First, the survey data are from a convenience sample from a small number of exposures and may not be representative of other veterinary clinical practices. Second, survey data were collected by various health departments during disease investigations and may be subject to reporting error or recall bias. Some data were collected months or even years after the initial investigation, which may have led to heterogeneity in how questions were asked and how data were collected.

Occupational transmission of F. tularensis in the veterinary clinical setting is rare but possible, particularly after high-risk exposures such as needlestick injury. Veterinary clinical staff should use workplace and practice controls to minimize needlestick injuries and use standard PPE. After a high-risk exposure to an animal with suspected or confirmed tularemia, such as direct contact with bodily fluid through a bite, scratch, or needlestick injury, veterinary staff should consider immediate PEP to prevent tularemia.