Technical | PPC106

The purpose of good pest management has always been to protect our health when certain animals come within problematic proximity to people.

We asked Dr Alex Kew from University College London Hospitals to look at the public health risks that arise from common pests to better educate and protect our clients.

SPEED VIEW:

• A study found at least 13 different infections in brown rats, with a few specimens having nine infections simultaneously
• Leptospirosis can be picked up from food contaminated with rodent urine
• Hantavirus symptoms include fever, low blood pressure, worsening shortness of breath and bloody or dark coloured urine that can look like Guinness
• A common symptom of cryptosporidium infection is severe watery diarrhoea which can persist for two weeks and, on occasion longer, especially in those with weakened immune systems
• The UK doesn’t have many insect-transmitted diseases that are found globally - however climate change may see many become endemic
• Untreated Lyme disease can go on to affect the nervous system, joints and heart
• Overseas pathogens can sometimes be easily transported to the UK by migratory birds.

Over the last 150 years or so, urban expansion has increased rapidly throughout the globe.

This has not only brought with it encroachment into the natural habitat of many wild organisms but has also provided highly adapted urban specialist species with an increasing amount of environment for them to exploit.

This increasing interaction, between humans and species considered pests, has also seen a marked increase in the number of zoonotic infections spread by these species.

In this article, we highlight a few of the more commonly seen infections to be aware of when dealing with some urban pests in the UK.

We also indicate the signs that members of the public can look out for, depending on the pest encountered.

Birds

Much like rodents, there are many pathogens associated with birds and transmitted by birds that can affect humans. Unlike rodents, birds have wings, so pathogens associated with other countries can sometimes be easily transported to the UK by migratory birds. 

We have not discussed every pathogen as it would make this article very long but have selected a few important infections to be aware of. These are split into bacteria and fungi. Avian flu is not discussed due to how it is managed and observed in the UK to prevent epidemic spread.

Bacteria

Psittacosis 
Caused by the bacterium Chlamydophila psittaci, transmission occurs after people come in contact with infected bird excrement or bird eye and beak discharge.

People tend to inhale the bacteria, which can go on to cause no illness at all or more severe infection ranging from a chest infection to systemic fever, enlarged organs and weakness. 

Pet owners, poultry workers and employment with close proximity to birds, nests and nesting sites increases the risk of infection.

Antibiotics are effective at treating psittacosis.

Pet owners, poultry workers and employment with close proximity to birds, nests and nesting sites increases the risk of infection.

Campylobacteriosis 
Caused by the bacterium Campylobacter jejuni, transmission occurs via bird droppings and aerosols.

Symptoms of campylobacter infection in persons with a normal immune system often include diarrhoea, abdominal cramps, and high temperatures. Diarrhoea can also be bloody with infection. 

Most patients do not require treatment with symptoms lasting less than a week. Those with severe symptoms or who become very unwell can be treated with rehydration and antibiotics.

Rarely, some patients can develop a rare post-infection neurological condition, called Guillain-barre syndrome, and should have an urgent medical review if symptoms of numbness and muscle weakness in the hands, feet, arms or legs and problems with balance occur.

Fungus

Cryptococcosis 
Caused by the yeast-like fungus Cryptococcus neoformans, transmission occurs after inhalation and exposure to bird droppings and contaminated soil.

Clinical disease is much more common in immunocompromised individuals, but infection can consist of chest infection, skin infection and meningitis.

Anti-fungal treatment is available for anyone with concerning features or exposure history, especially if they are immunocompromised.

Rodents

Rodents, primarily commensal rodents, have been associated with human disease and infection for hundreds if not thousands of years.

The black rat Rattus rattus, the brown rat Rattus norvegicus and the house mouse Mus musculus can spread many pathogens into urban dwellings. 

One study in the UK found at least 13 different infections in the brown rat population, with a few individual rodents being found to carry 9 of the 13 infections all at the same time.

Regular defecation and urination of rodents, and movement around food sources can pose a particular health risk. 

Rodents, primarily commensal rodents, have been associated with human disease and infection for hundreds if not thousands of years.

Bacteria

Salmonella/Vibrio/Listeria spp 
These are all bacteria that can be caught from handling rodents or their droppings and urine.

Illness associated with these bacteria can range from mild self-limiting gastroenteritis and diarrhoea to severe sepsis and multi-organ failure. 

By far and away the most common presentation, especially in people with normal immune systems, is of mild gastroenteritis, which can resolve on its own. 

Leptospirosis 
This infection, caused by the bacterium Leptospira, often appears in the news after outdoor water swimmers become unwell and need antibiotic therapy.

Although swimming in rivers and lakes can expose people to Leptospirosis, the infection can be spread by any exposure to rodent urine or other infected bodily fluids.

This exposure also includes drinking or eating food items that have become contaminated with rodent urine. 

Removing contaminated items and cleaning rodent urine and droppings, using correct precautions such as gloves and eye protection, is extremely important. Like many infections, Leptospirosis can be mild and self-limiting, presenting similarly to influenza. 

Although swimming in rivers and lakes can expose people to Leptospirosis, the infection can be spread by any exposure to rodent urine or other infected bodily fluids.

However, some presentations can be much more severe with continuous high fevers, rash, headaches, muscle aches, chills, jaundice, kidney failure and bleeding, including blood in the sputum, urine, or faeces.

Severe Leptospirosis is dangerous and so medical therapy should be sought immediately in someone presenting with severe symptoms so antibiotics can be administered.

Rat-bite fever 
Commonly caused by the bacteria Streptobacillus moniliformis in Europe, this infection is not only spread by bites/scratches of rodents, hence the name, but can be spread by consumption of rodent excrement, often when people consume contaminated food items. 

Symptoms can include rash, multiple painful joints, fevers, chills, headache, nausea, and vomiting. The infection can be significant and severe, and therefore antibiotic therapy is recommended for anyone suffering from rat-bite fever.

Parasites

Hantavirus 
This RNA virus is acquired following exposure to rodent saliva, urine and faeces, and can cause a clinical syndrome with similarities to severe Leptospirosis.

Symptoms can include a non-specific flu-like illness but can progress in some people to kidney failure. 

Much like Leptospirosis, anyone presenting with severe or worsening symptoms of fever, low blood pressure, worsening shortness of breath and bloody or dark coloured urine that can look like Guinness after rodent exposure, is advised to seek immediate medical review.

This RNA virus is acquired following exposure to rodent saliva, urine and faeces, and can cause a clinical syndrome with similarities to severe Leptospirosis.

Hymenolepiasis 
Hymenolepiasis is caused commonly by two species of tapeworm - the dwarf and rat tapeworm.

Infection happens when humans ingest rodent excrement in contaminated food items, infected arthropods within food items or consume unintended infected material such as soil. 

The infections themselves are often asymptomatic but can cause diarrhoea, abdominal pain, weakness and anorexia. 

Cryptosporidiosis 
Caused by the microscopic parasites Cryptosporidium spp, infection is caused when surfaces, unwashed hands, soil or water and food becomes contaminated with the faeces of infected rodents or other people. 

The most common symptom of cryptosporidium infection is severe watery diarrhoea, which can persist for two weeks and, on occasion, longer, especially in those with weakened immune systems.

Young children, pregnant women and those with weakened immune systems can be particularly at risk of more severe diarrhoea.

As we can see, a number of these infections are acquired by consuming items contaminated with rodent excrement.

Therefore any person with close contact or exposure to rodents should take extra precautions to make sure surfaces, food items and other materials are thrown away or decontaminated, and kept as clean and hygienic as possible.

Insects and arachnids

We are fortunate in the UK that many insect-transmitted diseases found globally, such as dengue and malaria, are not currently transmitted within our shores. 

Climate change will almost certainly change this fact, and we may see many of these infections become endemic in the UK but, for this article, we will focus on the few infections to be wary of when considering insect and arachnid pests. 

While there are many arthropod pests, each species can be broadly split into two categories: those that feed on human beings and those that do not.

Blood feeding insects and arachnids – Fleas, mosquitoes, mites, lice, bed bugs, ticks, biting flies

Cellulitis/infected bite 
The vast majority of infections that occur after arthropod bites in the UK are due to superadded bacterial infection. 

Our skin is a natural barrier to infection. As such, breaks in the skin from a bite may allow bacteria such as group A streptococcus and staphylococcus aureus to enter and cause infection of the skin, known as cellulitis, or localised infection of the bite site. 

Symptoms include hot, red, swollen, and painful skin with some bite lesions also discharging pus.

Preventing bites from occurring, and good skincare and hygiene after bites have occurred, can help prevent such infections from happening, but if an infection does occur, antibiotics usually are enough to treat the infection.

Skin infections can become severe, so a medical review should be sought if a bite or skin infection is present and worsening.

Lyme disease
Lyme disease is regularly mentioned in the national press and is caused primarily by the bacterium Borrelia burgdorferi.

Transmission in the UK occurs through the bite of infected Ixodes ticks and characteristic symptoms including a bullseye skin rash at the site of the bite called erythema migrans, as well as fever, headache, and fatigue. 

Untreated Lyme can go on to affect the nervous system, joints and heart. The best management is to prevent tick bites from happening in the first place, but if bitten and the characteristic symptoms appear, testing and treatment can be provided by medical practitioners.

Lyme disease is regularly mentioned in the national press and is caused primarily by the bacterium Borrelia burgdorferi.

Rickettsia felis/akari 
Two species of Rickettsia bacteria can and have been transmitted in the UK, but many species cause disease globally, and changes to the environment and climate may result in more species being observed in the UK.

R.felis is transmitted by flea bites and R.akari by mite bites. R.felis can present like other rickettsia illnesses with high fever, rash and muscle aches.

Antibiotic treatment is available, so a medical review is important if flea bitten people develop worsening symptoms as described above after flea bites. R.akari, otherwise known as rickettsial pox, is spread by house mouse mite bites and can also present with fevers and a rash.

R.akari, unlike felis, is typically self-limiting, with those normally affected not requiring treatment.

Mosquitoes 
As mentioned, in the not-too-distant future, we are likely to see more transmission of mosquito-borne pathogens. 

Malaria, spread by mosquitoes, was endemic in the UK, with the last outbreak occurring as recently as 1921.

As these pathogens spread further globally, illness resulting from a mosquito bite may become more severe than it currently is in the UK, requiring closer observation than mentioned here.

Infection of the skin after being bitten by a mosquito, as mentioned, is the most likely infection to occur.

Non-blood feeding insects – cockroaches, ants, wasps, beetles

Gastroenteritis 
Other than initial bites and stings from these insects that can lead to secondary bacterial skin infection as already mentioned, illness can be caused by these insects moving bacteria from a contaminated area into human dwellings and onto food items.

For example, cockroaches feeding and moving around human waste and then moving into kitchens and onto food and surfaces can contaminate those materials with the bacteria they collected on their bodies while moving around waste. 

Bacteria found in waste, like E. coli, can cause gastroenteritis when picked up from contaminated items. Most gastroenteritis acquired in this way is self-limiting, with good hydration being the mainstay of supportive care.

Occasionally, antibiotics are required for severe diarrhoea or ongoing worsening symptoms. Good protective food storage and pest removal can help prevent diarrhoeal illnesses from occurring.

...illness can be caused by these insects moving bacteria from a contaminated area into human dwellings and onto food items.

In summary

We have discussed some of the more common illnesses that can be acquired from exposure to UK pests. The vast majority of these infections can be prevented if proper protective gear, eyewear, and clothing are worn, especially when close to pests and their excrement. 

Lots of these infections can present the same way as other common illnesses. Therefore, good awareness of pest-related disease, as well as providing exposure history to medical professionals if people become unwell, can help guide the correct management. 

Any patients or staff with suspected animal-related injury or illness can be referred by their GP to the Hospital for Tropical Diseases in London for further advice, investigation and management if needed.

SEE ME AT PESTEX'22

“PestEx: Paws for thought – medical problems and infections from pests”

16 March at 10:30 in the Technical Theatre.

Register now

Source: PPC106