Occupational Hazards in Veterinarians: An Updating

Background: The veterinarian is a complex and varied work: risks in veterinary activity show are more typical of manual work than medical profession. Many reviews analyzed occupational risks related to veterinarians, but compared to the past current risks are more different. This review analyzes veterinary profession considering main occupational risk factors, as defined by World Health Organization: physical, chemical, biological or other agents that may cause harm to an exposed person in the workplace and is potentially modifiable. Methods: Publications investigating physical, chemical, biological, cancer and stress risk as well as effects associated with these exposures through veterinary practice were searched in the PubMed and Web of Science database. Publications were judged to be covered in the review when the following inclusion criteria applied: Articles should be published in the English language; Articles published after 2000; Studies reporting some numerical data about exposures and subjects considered; Studies concerning health effects regarding only veterinarians associated with exposure to animals, not general population. Results: Compared to the past, when the main risk of occupational disease was represented by zoonosis (in particular mycotic infections, mange, swine erysipelas, anthrax and tuberculosis), current risks are also represented by new entities such as mental and physical stress. However injuries, radiations, chemicals, zoonosis and allergies continue to represent a considerable portion of professional risks. Conclusions: Zoonosis, injuries and trauma remain the main occupational risk for veterinarians today, but new emerging risks, such as psychological risks are becoming increasingly important for these workers.


Introduction
Veterinary medicine is the science that deals with the health and welfare of animals, particularly with regard to the prevention and cure of diseases. Since the health of humans is connected to the health of animals and the environment, veterinarian protects human health by controlling diseases that are transmitted from animals to humans (zoonoses) and ensuring the health check on foodstuffs of animal origin.
The veterinarian job is a complex and varied work and the risk to undergone by to prove it. The risks in veterinary activity show are typical of the medical profession that manual work.
The veterinarians are employed in a large field of activities, ranging from animal health and welfare to food safety and public health [1]: Companion animal veterinarians, who treat pets and generally work in private clinics; Equine veterinarians, who work with horses; Food animal veterinarians, who work with farm animals such as pigs, cattle, sheep, goats, poultry and other food producing animals as Food safety and inspection veterinarians, veterinary public health concerns all aspects of food production chain from controlling transmissible diseases that may impact on human health to slaughter procedures and inspection of carcasses and products until their sale on the stores; in this field they are made to check on animal products from abroad in order to ensure safe food supplies; Research veterinarians, who work in laboratories, conducting research on human and animal health problems. These veterinarians may perform tests on experimental animals for example to identify the effects of new drug therapies, or they may test new surgical techniques. They may also research how to prevent, control, or eliminate food-and animal-borne illnesses and diseases. Also there are veterinarians who deal with experimental animals, to ensure their health and welfare; Veterinarians who work in laboratories, they deal with diagnostic procedures with various specializations: pathological anatomy, microbiology, virology, pharmacology, chemistry applied to foods, immunology, etc.
Veterinarians perform different tasks that can be counted among those at risk for health and safety, in particular herds of animals, lairages, slaughter houses, farms larvae, stables, horse stables and meat processing plans, and much different tasks that relate in various ways to the problem (and risks) Bovine Spongiform Encephalopathy (BSE).
Compared to the past, when the main risk of occupational disease was represented by zoonosis (in particular mycotic infections, mange, swine erysipelas, anthrax and tuberculosis), current risks are also represented by new entities such as mental and physical stress [2]. However injuries, radiations, chemicals, zoonosis and allergies continue to represent a considerable portion of professional risks ( Figure 1) [2,3].

Materials and Methods
Definition of veterinary profession risk factors: This paper analyzes veterinary profession considering main occupational risk factors, as defined by World Health Organization (WHO) [4], physical, chemical, biological or other agents that may cause harm to an exposed person in the workplace and is potentially modifiable.
The main physical risks for veterinary profession are injuries/ trauma/musculoskeletal disorders and ionizing radiations. Chemical risk can result mainly from the use of gaseous anesthetics, drugs (and in particular antineoplastic and antiparasitic agents), detergents and disinfectants. Biological risk is present in all work activities where there is risk of exposure to biological agents that is any organism that may cause infection, allergy or poisoning.
Literature search: Publications investigating physical, chemical, biological, cancer and stress risk as well as effects associated with these exposures through veterinary practice were searched in the PubMed and Web of Science databases. The following search terms were utilized: "occupational exposure", "physical risk", "chemical risk", and "biological risk", "stress", linked with the word "veterinary" or "animal". Publications were judged to be covered in the review when the following inclusion criteria applied: Articles should be published in the English language; Articles published after 2000; Studies reporting some numerical data about exposures and subjects considered; Studies concerning health effects regarding only veterinarians associated with exposure to animals, not general population.
Another kind of physical exposure regards radiations; we found 9 studies [3,9,12,[29][30][31][32][33][34]] about this risk (Table 1): the majority of the exposures were below the annual limit of 20 mSv/year recommended by International Commission on Radiological Protection [35], except for one study [9]. Some authors reported an increased risk of spontaneous abortion for pregnant medical staff [3,30,31]. In particular dose received by the assistant is on average 6 times higher than the dose received by the veterinarian, and sometimes the received dose is comparable with the recommended limit [34].
Noise is a well-known physical risk factor for several occupational activities, but in veterinary facilities do not normally exist situations or machines that subjecting operators to noises that exceed those permitted.
Hearing loss has not been widely reported in the veterinarians profession: we found only 2 studies published before 2000 [9,36], but also in these cases there was a small percentage of vets denounced hearing loss.
There are few publications on quantitative exposure to pesticides in the veterinary profession, and they are all published before 2000.
In Figure 1 we summarized published paper we found about biological risks in veterinary medicine.
Little is known about the prevalence, diagnosis and treatment of zoonotic disease among veterinarians: in our review we found an incidence of zoonosis ranging from 16.6% to 65.7% [9,[42][43][44][45].
The main zoonotic agents we found in our review are reported in Table 3.

Agent
No of studies
The contact and the manipulation of animals can determine the appearance of numerous clinical forms allergic. The prevalence of allergic diseases increased with the length of occupational exposure and female veterinarians in practice were more likely to develop allergies than were male veterinarians [5,9]; in our review we found an incidence of zoonosis ranging from 5% to 63% [9,12,36,63,64,68,89], with the highest incidence reported for respiratory symptoms (5,12,(63)(64)(65)90,91). Rhinitis was the most frequent one, followed by cough/chest tightness, wheezing and airways obstruction. 6 studies reported skin problems: dermatosis was the most frequent disease [12,63,64,66,89,92].
Occupational health problems arising from mental or physical fatigue have rarely been assessed. Veterinarians, especially practice principals, have an enormous responsibility in managing a veterinary practice. In Figure 1 are represented studies concerning stress we found in our review.
Some stress is necessary for achieving one's best performance, but poorly managed stress can result in burnout, substance abuse, depression, anxiety, relationship distress, a negative work-home life environment, and even suicide [98,99,103-106].

Discussion
In this paper we analyzed veterinary profession considering main occupational risk factors: physical, chemical and biological, next to an emerging risk factor: psychological risk.
Many studies on veterinary profession have demonstrated that veterinary work is physically demanding and poses an elevated risk of severe injuries and/or trauma: from the analysis of literature we did, we can affirm that physical risk (which includes injuries/trauma, radiation and noise) remain one of the main risk factors for veterinary activities.
Trauma include bites, scratches and injuries caused by animals to handling errors and containment of the animals themselves; injuries from sharp instruments such as syringes, needles, scalpel blades, nose tongs for cattle, halters, calf pulling equipment, metal cattle chutes and injuries from falls on slippery surfaces. Large animals and cattle was the species most likely to cause injury, predominantly in the upper extremities, but also dog bites, cat bites and scratches and horse kicks resulted particularly dangerous [5]. Sharp instruments are a frequent agent of injuries, but it is unlikely that they cause severe injuries alone: more likely it will be the chemical or biological agents introduced that cause severe problems [16].
In addition to acute injuries, veterinarians suffer from Repetitive Strain injuries or Musculoskeletal disorders (MSD), best known in literature as "Work-Related Musculoskeletal Disorders of Upper Extremities" (WRMSDs-UE), which are inflammatory and degenerative disorders responsible for pain and functional impairment in tendons, muscles, joints, nerves or blood vessels. Static or awkward postures, repetitive or forceful tasks may be risk factors for the development of MSD in the upper extremities and backbone, and it could make worse by pressure of time, work stress, career structure and after hours duties [12,24,107]. Some practitioners, in particular those employed in imaging, work with one or both arms above shoulder level for over one hour daily [23], and this could be an important risk factor for the development of MSD in the upper extremities.
Another kind of physical exposure regards ionizing radiations: it is thought that most practicing veterinarians use radiographic equipment; this occurrence is more frequently in veterinary procedures since the animals must be restrained and therefore the operator could be very close to the source of radiations. Despite this, it seems that veterinarians currently have lower exposures than radiologists and surgeons: the majority of the exposures we found were below the annual limit of 20 mSv/year, except one [9]. There are known risks of skin cancer, thyroid cancer, and leukaemia with exposure to Xrays, but the doses received in veterinary practice are probably insufficient to cause major increases in risk, unless there are problems with the equipment or with radiology procedures.
Noise is a well-known risk factor for several occupational activities, but hearing loss has not been widely reported in the veterinary profession: actually in veterinary facilities do not normally exist situations or machines that subjecting operators to noises that exceed those permitted.
Chemical risk appeared to be less relevant than physical and biological risk, but it could be due to undernotification of claims, which it is not always easy to recognize the causal link: many substances used in veterinary practice may accidentally be split on the skin, inhaled, ingested or injected and can cause hazardous effects, which include mutagenicity, teratogenicity, carcinogenity, acute toxicity, flammability, explosiveness, skin irritation, allergic reactions and lung damage.
Among chemicals, the majority of exposures regards anesthetics gases: dispersion of these chemical compounds in the operating room depends on several factors (conveyance and disposal of gas, the quality and amount of ventilation of the room, taking into account the issue of the gas inhaled by the animal anesthetized through the respiratory tract); although there are no statistical data on their concentration, it is possible to assume, on the basis of known concentrations of the same hospital halls, that an exhibition is not indifferent. Anesthetics are then accused of disorders of the central nervous system and peripheral, liver (especially halothane) and kidney; females were more likely to experience adverse reactions, which included headache, nausea, sleepiness and dizziness [16]. The risk of adverse pregnancy outcome or spontaneous abortion has been analyzed in several studies [30,38,108-110], but, thus far, the results have been inconclusive. Also the evidence of cancerogenicity of volatile anaesthetics was an important risk factor: its role was reviewed by IARC 1987. In the past years some authors reported an increase in lymphohaemopoietic and pancreatic cancer but these were not consistent [33, 111,112] and actually we didn't find any recent work about this topic.
Drugs, in particular antineoplastic drugs are a potential problem for the operator private veterinarian, since the chemotherapy is an increasing practice for pets and thus the existence of such risk entails the necessary allocation of appropriate protective equipment (gloves, masks, chemical hood, etc.).
Drugs can also cause allergic contact dermatitis and antibiotics are the most common sensitizers [93]. It has been suggested that prostaglandins could cause adverse respiratory conditions and abortion [2]: in past years Wilkins and Bowman reported a spontaneous abortion after an accidental self -injection of a prostaglandin compound [113].
Detergents, disinfectants and pesticides are used directly on animals to control parasites or applied to the area where animals are confined for cleaning and disinfection of premises, equipment and tools for the prevention of infectious and contagious diseases, postoperative and iatrogenic infections. They may present hazards to contact (burns), inhalation (inflammation of the mucous membranes of the respiratory tract and ocular-conjunctival) and special attention should be paid to products that cause toxic, carcinogenic and teratogenic effects.
There are few publications on quantitative exposure to pesticides in the veterinary profession, and they are all published before 2000: some veterinarians had experienced mild symptoms of poisoning, but there was no consistent and progressive depression of blood cholinesterase activities [114]. Handlers who used flea control products were significantly more likely to report symptoms such as skin rash, tearing, unusual tiredness, burning of the eyes and flushing of skin [115]. Some studies in the past demonstrated that use of flea and tick dips could be a risk factor for cancer: Glickman showed that these substances could be a risk factor for bladder cancer in dogs, but the relevance of this to human carcinogenesis is unknown [116], while a case-control study examined the risk of non-Hodgkin's lymphoma with use of lindane: they found a slight significant increase in the risk with ever use of lindane [117].
Biological risk continued to be the main occupational risk for vets: it is present in all work activities where there is risk of exposure to biological agents. Zoonosis and allergic reactions (respiratory symptoms or allergic contact dermatitis) to animal hair, dandruff and feathers proved to be the most frequent cause of all verified occupational diseases in veterinary practice [5]. NIOSH reports that there are approximately two million workers with jobs requiring constant handling of animals [120].
A zoonosis can be defined as "any disease or infection caused by all types of agents (bacteria, parasites, fungi, viruses and unconventional agents) transmissible from vertebrate animals to humans and viceversa" [121]; as for biological risk from zoonoses is difficult to express the extent of damage expected: the consequences of exposure to the most common zoonotic agents may vary from the simple seroconversion to the disease with extremely variable symptomatic manifestations until the onset of irreversible sequelae or death. Damage is conditioned by different parameters such as infectious dose received, pathogenicity of the strain, individual immune status, presence of risk factors such as drug treatments, disease or intercurrent infection, age, physiological state (pregnancy).
Little is known about the prevalence, diagnosis and treatment of zoonotic disease among veterinarians; in our review we found an incidence of zoonosis ranging from 16.6% to 65.7% [9,[42][43][44][45].
During recent decades, the public health risk represented by zoonosis was suggested by the onset of previously unknown human infection diseases that emerged from animal reservoirs such as Ebola virus, West Nile virus, Creutzfeld-Jakob diseases [9,141].
Zoonosis are also suspected to bring about an increased risk of cancer, as suggested by some epidemiological data showing that veterinarians, meat inspectors and slaughterhouse workers experience an increased risk of myelolymphoproliferative disorders attributed to contact with animal oncoviruses, in particular those associated with poultry and cattle farming [142][143][144][145][146]. Exposure to oncogenic viruses, in particular papillomaviruses, could also be an etiologic agent of esophageal cancer in cattle and humans: some studies reported an increased risk of esophageal cancer in veterinarians [135,147].
Fortunately cancer risk in general seems to be declining: in our literature review we didn't find any recent study about this topic. This could be due to a better awareness of occupational risks, in addition to a reduction of carcinogens, in particular physical (radiation) and chemical agents, and to the application of protective measures, both collective and individual.
The contact and the manipulation of animals can also determine the appearance of numerous clinical forms allergic. The prevalence of allergic diseases increased with the length of occupational exposure [16]; female veterinarians in practice appeared to be more likely to develop allergies than were male veterinarians [9].
This occupational disease affects veterinary staff who have daily contact and close to the animals [67], the staff becomes more sensitive to inhaled allergens suspended in the atmosphere or as a result of abrasion, scratches or bites. The majority of the allergens can be defined as bio-aerosol, dust with a heterogeneous composition containing many toxic and immunogenic particles, for instance pathogenic and/or non-pathogenic microorganisms (bacteria, viruses and fungi) and their biological active components (bacterial endotoxin, mycotoxin), plant fragments (pollen) and animal-derived materials (hair, dander and allergens) and these allergens are associated with mammalians, such as cows, horses, cats, dogs, rats and mice [9,[65][66][67]148].
Rats and mice are the animals most commonly used in scientific experimental studies: occupational exposure to these animals often occurs when working with laboratory animals. The prevalence of allergy against rats in laboratory animal's workers ranged from 12-31% in some recent studies, and for mice ranged from 10-32% [149,150]. Several epidemiological studies showed a strong association between intensity of exposure to laboratory animal allergens and elevated prevalence of LAA [151,152]: this higher prevalence of allergy against rats and mice, compared to other animal allergens, is probably due to the more frequent use of these animals in experimental studies, and not to lesser ability of other animal allergens to trigger allergy [67].
veterinarians interviewed in American studies reported a skin reaction to latex gloves [36].
In the past years contact with biological agents, in particular mycotoxins and bacterial endotoxins, could also result in poisoning. Mycotoxins are toxic substances produced by the metabolism of fungi or molds, which develop, under certain conditions on grass silage, grain and feed business or industrial; the most common agents are Aspergillus, whose aflatoxin is carcinogenic, hepatotoxic, immunosuppressant, Fusarium, whose fumonisin is neurotoxic, carcinogenic, genotoxic and zearalenone is estrogen-like, and Penicillium, whose ochratoxin is nephrotoxic, teratogenic, immunosuppressant and carcinogenic [153]. Contamination can occur on the field or during the later stages of transport, processing and storage.
While the mycete can be considered a pathogen for the plant, ingestion of mycotoxins can cause acute and chronic toxicity in humans and in animals.
Plants most frequently at risk to cause intoxication are peanuts and derivatives, flour and corn germ, corn gluten feed and corn grain; symptoms than can occur are divided in acute and chronic: the former include systemic and respiratory symptoms due to increasing of inflammatory response, while the second include an accelerated lung function decline [154,155]; in our revision of literature we didn't find any recent paper about this topic: notification could be underestimated, especially in poorer countries. It's also probable a real decrement of their incidence thanks to an improvement in information and prevention of this risk.
Occupational health problems arising from mental or physical fatigue have rarely been assessed, but this risk seems to become increasingly important in the last years. Veterinarians, especially practice principals, have an enormous responsibility in managing a veterinary practice; this includes activities such as ordering chemicals and drugs, overseeing the running of the hospital, supervising the business operation, medical and surgical management and generally being involved in community activities such as speaking at local meetings and schools: this combination of work and non-job responsibilities can cause considerable mental stress, burn-out and also an increased risk of suicide.
Sources of stress that create poor wellness in veterinarians include giving bad news, managing adverse events, long hours worked by day, clients expectations, working in teams, and balancing work and home life. But handling ethical dilemmas, in particular regarding euthanasia (especially among veterinarians involved in small animal and equine work [12,95,96,99,[156][157][158], seemed to be the worst stressor. Some stress is necessary for achieving one's best performance, but poorly managed stress can result in burnout, substance abuse, depression, anxiety, relationship distress, abuse of tobacco, alcohol and drugs, a negative work-home life environment, and even suicide, in particular in women and younger vets [12,94,99,100,[101][102][103][104][105][106]159,160].

Conclusions
The analysis of recent works about veterinarian occupational risks showed some changes compared to the past.
Biological risk (zoonosis) remained the most common risk represented in literature: MRSA, Coxiella burnetii and Brucella spp were the most common infections for vets. Beside this risk, injuries and trauma remained an important risk factor, probably due to intensive working rhythms and pressure of time.
Compared to the past the main change was represented by mental stress and suicide risk arising from mental or physical fatigue, which became increasingly important in the last years.
Ionizing radiation risk is still represented, even if the majority of works we analyzed did not consider it as a risk because doses did not exceed the maximum level permitted.
Chemical risk, in particular anesthetics and drugs remained an important risk for pregnant women, even if results were inconclusive. Also allergic risk was still present in literature: it was related to bioaerosol in particular, but also to drugs, detergents and disinfectant exposure.
Noise risk was not represented in our review: compared to the past it became a marginal risk thanks to PPE and technological improvements.