TECHNICAL | PPC101 DECEMBER 2020
Anyone who works around animals has an increased risk of picking up or passing on a nasty zoonotic disease. As pest professionals, it’s up to us to be able to protect ourselves, our clients and our clients’ clients from the diseases pest species can transmit.
We asked Dr Adrienne Mackintosh, a Veterinary Investigation Officer for the Animal and Plant Health Agency (APHA) to share her knowledge of zoonoses with PPC readers so we can better assess the risks.
SPEED VIEW
- Zoonotic diseases can be caused by bacteria, viruses, parasites, fungi and protozoa
- Occupational risks have typically been recognised for those with direct contact with animals or animal products
- COVID-19 has highlighted that many emerging diseases are of animal origin
- Advice about protective measures including wearing PPE and RPE should always be adhered to.
We most often talk about zoonotic diseases being human infections of animal origin but, as a vet, I’m also inclined to remind people that humans may be the source of infection to animals. The World Health Organisation (WHO) defines zoonotic diseases as “diseases and infections which are transmitted naturally between vertebrate animals and man”1.
Zoonotic diseases can be caused by bacteria, viruses, parasites, fungi and protozoa. Disease may be acquired by direct contact with the animal or indirect contact, via the environment, clothing and other fomites contaminated by animal secretions or excretions. Foodborne and waterborne zoonoses occur through contaminated foodstuffs and water supplies respectively.
There are lots of longstanding diseases that have zoonotic potential such as Salmonellosis, Leptospirosis, and Brucellosis, but new diseases like SARS and, most recently, COVID-19 have highlighted that many emerging diseases are of animal origin. It is estimated that up to 75% of newly emerging diseases are zoonotic2.
Many zoonotic diseases are capable of causing serious, potentially fatal, illness in humans, eg haemolytic uraemic syndrome (HUS) due to E. coli O157 infection, leptospirosis or hantavirus. Less serious diseases still have a significant economic impact in lost work days and there is a potential risk of passing infection to others – so-called secondary cases.
The infectious agent may be excreted in a number of ways including, but not limited to faeces, saliva, urine, pus, blood, and birth products. The source doesn’t determine how a person is infected; common infection routes are shown in the table.
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Route
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Risk activities
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Mitigation
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Ingestion
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Eating, drinking, smoking and nail biting. Any activity that transports the infectious agent to the mouth is a risk.
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Good hand hygiene including washing with hot soapy water and the use of gloves.
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Inhalation
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Airborne water droplets - eg if the agent is aerosolised for example by high-pressure washing. Dust - If an infectious secretion dries, dust may be released when the area is disturbed, for example, animal bedding.
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Appropriate respiratory protective equipment, minimising the chances of aerosolisation or creation of dust.
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Skin
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Infection may be acquired if there is contact to an abrasion or skin wound, sometimes this is even possible through intact healthy skin.
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Good hand hygiene including washing with hot soapy water, wear gloves as appropriate, cover cuts or abrasions.
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Mucus membranes
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These are the membranes at the junction of skin and internal areas of your body, such as conjunctiva in your eyes, or gums and cheeks inside your mouth.
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Avoid splashing of, eg potentially infected water or urine, wear personal protective equipment (PPE) such as eye protection and masks as appropriate.
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With the exception of food and waterborne zoonosis, disease transmission is most likely when there is close or prolonged contact with an infected animal or its environment.
There is an increased risk of disease in certain occupations or activities. Occupational risks have typically been recognised for those with direct contact with animals or animal product like vets, farmers and abattoir workers, and those with increased contact to potentially contaminated environments such as forestry workers, sewage workers and outdoors activity instructors. Pest control technicians would fall into both of these occupational risk categories.
For the purposes of this article, some occupational zoonoses associated with exposure to pests will be explored a little further. In addition to infectious agents associated with the target pest, pest control technicians should also be mindful of potential hazards associated with the premises and its primary function. If that primary function includes animals or animal product there will be additional potential zoonoses to consider.
Examples of zoonoses to consider in a pest control role
This is not an exhaustive list and any new environment should be researched for potential hazards.
Salmonellosis
Salmonellosis in humans may present with varying clinical severity and a combination of nausea, vomiting, diarrhoea, stomach cramps fever and general malaise3.
All Salmonella should be considered to have zoonotic potential, but the Salmonella serovars primarily of interest in zoonotic outbreaks are Salmonella Enteritidis and Salmonella Typhimurium.
Rodents play an important role in spreading, maintaining and amplifying Salmonella infection in premises, and this is particularly important in poultry. Vaccination is used in some livestock species to help reduce disease and environmental contamination.
Transmission is by direct and indirect contact, and infection is typically by ingestion.
Hantavirus infection
Hantavirus can present in humans with a range of symptoms from mild flu-like illness to severe respiratory disease, or haemorrhagic disease with kidney involvement.
Infected rodents shed the virus in urine, faeces and saliva. Generally, infection in humans is by breathing in dust and virus from the infected environment4.
Q fever
Disease in humans is often mild, but symptoms may include flu-like illness, fever and tiredness, pneumonia or other complications including longer-term illness and, rarely, heart valve infection. There is a particular risk to pregnant women with the possibility of premature birth, low birth weight or abortion.
Q fever is caused by Coxiella burnetii and is associated with the products of birth and abortion usually in livestock such as sheep, goats and cows, but may also be carried by other animals including rodents.
People are generally infected by inhalation of infective particles on dust or water droplets.
Leptospirosis (Weil’s disease)
Symptoms and severity in humans may vary but include; high temperature, headaches, nausea muscle and joint pain. In severe cases jaundice, swelling, breathlessness and coughing up blood3.
Leptospirosis may be associated with rodents and their environment such as ditches and watercourses.
Transmission can be direct or indirect via eg contaminated water. Inhalation of aerosols, skin contact or via mucus membranes are all potential routes of infection for Leptospirosis.
There are several different serotypes of Leptospira and vaccination is used in some livestock species and pets to help control disease.
Psittacosis
Disease in humans is characterised by fever, headache, muscle pain and a dry cough4.
Psittacosis is caused by Chlamydia psittaci and is primarily associated with psittacine birds – the parrot family, but can affect other species, including wild birds and pigeons. Disease in humans and psittacines is called psittacosis. The same disease in birds not of the psittacine family is called ornithosis or avian chlamydiosis.
Transmission is by direct and indirect contact and is typically by inhalation. The elementary bodies are highly resistant and can survive in dried faeces for months.
Toxoplasmosis
Disease in humans may vary, but include a combination of fever, muscle aches and swollen glands. Immunocompromised people are at particular risk of severe disease, and there is a significant risk to pregnancy. Disease can be passed to the unborn child and cause serious complications including miscarriage3.
Toxoplasmosis caused by Toxplasma gondii has a life cycle where the cat is the final host and a number of animals including humans and sheep can act as an intermediate host. Humans become infected after eating infective cysts in undercooked meat, or from infected cat faeces.
Vaccination is used to help control disease in sheep as an intermediate host.
Cryptosporidiosis
In humans, diarrhoea, stomach pain, vomiting and fever are all associated with cryptosporidium infection4. Disease may be more severe in immunocompromised individuals.
There are many different species but, C. parvum is most likely to be associated with disease of animal origin. Disease is typically associated with close contact with young ruminants (such as lambs or calves) or their environments.
Infection is by the oral route and may be direct or indirect with large numbers of infective oocysts shed in the faeces of infected animals and people.
Individual and role-related protective measures including wearing PPE and RPE should always be adhered to, hopefully this short article has re-enforced some of the reasons why.
If an individual were to become unwell, they should seek medical advice and make their medical practitioner aware of occupational risks – so please tell the doctor what your job is and what you may have come into contact with. This could help speed up diagnosis and any necessary treatment.
References and further reading
- WHO. Zoonoses. 2020
- Salyer, SJ, et al., Prioritising zoonoses for global health capacity building – themes from one health zoonotic disease workshops in seven countries, 2014-2016. Emerging Infectious Diseases, 2017. 23: p. S57-S64
- NHS. NHS website. 2019 (cited 2019 26/10/2019)
- CDC. Centre for Disease Control and Prevention. 2020
- PHE. Hantavirus 2008 (14/09/2020).
Source: PPC101