Feature articles

22 May 2019

RODENT RISKS: Pest closure and prosecution stories

Health and safety | PPC95 May 2019

Pest infestations, particularly associated with rodents, cause more emergency closures of food businesses than virtually anything else. When googling ‘rodent risks’, you could be forgiven for thinking that your time is up if you dare even to go near rodent-infested premises.

In this article, Dr Belinda Stuart-Moonlight, of Moonlight Environmental, aims to give a more balanced and evidence-based view of the dangers associated with rodent infestations in food businesses.

SPEED READ:

  • Some diseases are carried by rats but not mice, some by mice but not rats, but the majority are carried by both
  • Rodents can pass other forms of contamination onto food packaging and directly into foods simply by moving about
  • There are many different requirements which a food business can fall foul
  • In assessing risk, one must consider how well the pathogens survive in the environment
  • The criterion used to determine whether a food business should be closed because of an infestation is whether there is an ‘imminent risk to health’
  • Variation in fines highlights that other factors such as the business’s turnover are also considered at sentence.

Clousure and prosecution stories - Rodent risks

As an expert witness in food safety cases in the UK criminal and civil courts, this is my bread and butter – explaining what is real, as opposed to received wisdom. I have no bias: I take instruction both from prosecuting local authorities, and food businesses on the defence. I focus on the science.

In this article, I shall:

  • Outline the biological and allergenic dangers associated with rodents
  • Outline the relevant law that applies to food businesses in the UK
  • Explore the likelihood of food contamination and illness
  • Comment on some recent prosecutions.

Risks associated with rodents

Zoonotic infections are those that are transmissible from animals to humans. Some diseases are carried by rats but not mice, some by mice but not rats, but the majority are carried by both.

Diseases prevalent historically, such as bubonic plague, may not be relevant nowadays in the UK. Others are ‘emerging zoonoses’; that is, diseases that are either on the increase or ones where our knowledge, understanding and ability to detect are improving: an example is Hantavirus.

Zoonotic infections associated with rodents worthy of consideration include:

  • Campylobacter
  • Cryptosporidium parvum
  • Hantavirus
  • Leptospirosis
  • Lymphocytic choriomeningitis virus (LCMV)
  • Q Fever
  • Salmonella
  • Toxoplasma gondii.

Rodents can pass other forms of contamination (physical, microbiological, chemical and allergenic) onto food packaging and directly into foods simply by moving about. This article, however, focuses on rodents being a reservoir of zoonoses, in other words being infected and passing the disease with which they may be affected, onto people directly or indirectly through food.

An additional non-food-related health hazard associated with rodents is an allergic reaction. Mouse urine contains a small lipocalin protein thought to be a territorial scent-marker, this is considered to be a risk factor for allergic sensitisation and asthma.

Routes of transmission

In considering risks in food businesses, it is important to note that zoonoses will be present in different types of rodent excretion and will gain access to human bodies in different ways:
Rodent excretions in which zoonoses can be present include:

  • Saliva (eg rats, Hantavirus)
  • Urine (eg mice, LCMV)
  • Blood (eg mice, Salmonella typhimurium)
  • Faeces (eg rats and mice, Campylobacter)
  • Birth products (eg mice, LCMV).
  • Routes of transmission include:
  • Faeco-oral (direct and indirect contamination)
  • Inhalation
  • Skin/mucus membranes
  • Injection (eg from a bite).

The presence of rats and mice in premises that sell or serve food is always undesirableFood law and offences relating to food businesses

In relation to pests there are many different requirements to which a food business can fall foul:

  • Failure to keep clean (EC:852 Annex II Cpt I 1)
  • Failure in the food safety management system (EC:852 Article 5)
  • Adequate procedures to control pests (EC:852 Annex II Cpt IX 4)
  • Maintenance (structure) (EC:852 Annex II Cpt I 2c)
  • Protection of food from contamination likely to render it unfit, injurious to health or contaminated (EC:852 Annex II Cpt IX 3)
  • Withdrawal of products from the market not in compliance with food safety requirements (EC:178 Article 19 (1))
  • Not placing food on the market that is unsafe (injurious or unfit) (EC:178 Article 14).

Food business closure

What should a pest controller see as significant?

Risks increase where rodents are in close proximity to open, high-risk food: that is, food that normally requires refrigeration and is ready to eat. An active infestation that has extended out of dry stores into kitchens or food manufacturing and packaging areas will be a concern.

What should a pest controller see as significant?

Risks increase where rodents are in close proximity to open, high-risk food: that is, food that normally requires refrigeration and is ready to eat. An active infestation that has extended out of dry stores into kitchens or food manufacturing and packaging areas will be a concern.

Moist and nutrient-rich surfaces favour survival of most bacteria

The presence of diseased animals should also warrant a more robust control strategy

Likelihood of contamination and illness - pathogen presence in hosts, pathogen survival in the environment, ease of transmission during cross contamination and infective dose.

There is a world of difference between knowing that rodents have the potential to carry and pass on disease and this actually happening.

Rodents can only pass on zoonoses if they are already infected. For instance, most rodents are not infected with salmonella. It is not part of the normal flora of rodent intestines: it would only be present if the animal had ingested the pathogen; the most likely sources are farms or abattoirs. There is arguably less chance of a rodent being infected in urban situations than in a rural one.

In assessing risk, one must consider how well the pathogens survive in the environment. Over time they dry, but some are much more resistant than others. The surface on which they are deposited will also influence survival. Moist and nutrient-rich surfaces favour survival of most bacteria. Even where pathogens survive in the environment, they can be killed or sub-lethally injured, meaning they could not give rise to illness in a human.

Finally, and crucially, enough of the pathogens would need to be transmitted to a human in order to cause disease – an infective dose.

The amounts may differ depending on whether the unfortunate recipient is more or less vulnerable (eg very young, old, pregnant or immune-suppressed).

About Belinda

Dr Belinda Stuart-Moonlight, Managing Director Moonlight Environmental, is a chartered environmental health practitioner and expert witness. She started out as an EHO before carrying out disease risk research at King’s College, University of London. She currently undertakes consultancy, auditing and training but more than half of her work is as an expert witness in the fields of infectious intestinal disease, food and health and safety. She examines risks and their control. She has worked on notable rodent infestation cases and regularly appears on BBC Watchdog and radio talking about microbiological risk.

moonlightenvironmental.co.uk

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Source: PPC95

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