Bites and Infestations

Bites from insects are incredibly common in the UK. Thankfully, the majority of these will be self-managed by patients, and those that do present to the Emergency Department (ED) are often easy to spot and treat. This blog will focus on some of the finer details in bite management, or complications that may be seen. (Apologies in advance for any itching caused by this blog).

Typical approach

Bites can trigger allergic reactions and so the possibility of this always needs to be considered. For most bites, a brief history about timing, location of rash, associated symptoms (such as pain, fever, itching) will be helpful. A recent travel history is essential (even if in the UK) as it is important to know what type of insect the patient may have been exposed to. Covering bites sustained outside the UK is too large a topic to cover in this blog, but obviously the differential diagnosis is wide depending on location.

For infestations (e.g. a chronic invasion of the skin), itching may predominate and there may be visible lesions in the skin. In terms of UK infestations, scabies and head lice are the most commonly seen.

One differential to be aware of is delusional parasitosis, where a patient may believe they are infested with an organism despite no evidence of this. This can be from a primary mental health disorder but also can be caused by a vitamin deficiency, renal failure or CNS disorder to name but a few!

Fig. 1 – RCEMLearning image generated with Google Gemini

What’s eating you?

Often the bites will not be witnessed. NICE CKS suggests some clues as to what’s caused the bite. Often this doesn’t change management but can be useful in deciding what to advise patients about the risk of infestation in the home. Below are some examples.

Bed bugs – Itchy, maculopapular rash with haemorrhagic punctums. Often associated with bites in several members of the same household.

Fig.2 – Image via Dermnet NZ. Bed bug infestation

Tick bites – often a tick can be spotted in the skin. Lyme disease can present with the classic “bullseye” rash of erythema migrans (seen below). Typically in high risk areas e.g. sheep fields, long grass, rural areas.

Fig. 3 – Image via Dermnet NZ. Erythema migrans

Scabies – caused by parasite Sarcoptes scabei. This is a human parasite and not caught by household pets etc.

Typically characterised by intensely itchy lesions (caused by the reaction to mite eggs), with lesions commonly seen on the hands, waist, genitalia, buttocks  and extensor surfaces of limbs. It can also be a sexually transmitted infection. Burrows may be seen, particularly between digits.

A severe variant known as crusted scabies can occur in immunosuppressed patients and is highly infectious.

Fig. 4 – Image via Dermnet NZ. Scabies images

Fig. 5 – Image via Dermnet NZ. Scabies images

How to treat – First aid

For a simple bite without signs of infection in the UK, simple first aid care will suffice. If there are any obvious insect parts visible removing these is indicated. Simple over-the-counter measures can help e.g. emollients, calamine lotion for itch, hydrocortisone cream or simple analgesia.

Specific management

Tick bites

Ticks (in the UK most commonly Ixodes Ricinus – see below) are commonly linked to Lyme disease (or Lyme borreliosis), caused by spirochaetes.  

Most people will have heard of the erythema migrans rash – a bullseye rash that can start from 1 day after a bite up to 6 weeks afterwards. It’s important to counsel patients about this timescale and what to watch out for. This is clinical Lyme disease and should be treated without any further testing. In the UK this is typically with a course of Doxycycline.

Important to note that a third of patients with early Lyme do not have erythema migrans, and may only have flu-like symptoms.

If not treated, a significant proportion of patients can go on to develop early disseminated disease. This can present with lots of small erythema migrans lesions, but includes serious complications such as meningitis and cranial nerve palsies.

Fig. 6 – RCEMLearning image generated with Google Gemini

Scabies

Scabies is highly infectious, and a key principle of treatment is ensuring anyone who has been a close contact of the patient also receives scabies treatment (usually Permethrin 5% topically).

The cream is applied all over the body and left on overnight. It is then washed off, and a second treatment is administered 1 week later.

At the same time, hygiene precautions are indicated ,e.g. washing all bedding on a high heat setting, not sharing bedding etc.

For crusted scabies the patient may require hospital admission for management. If so, strict infection control is needed.

Snake bites

For most bites from possible venomous animals, identification is key, as this allows for screening for worrying or concerning symptoms and administering antidotes.

In the UK the adder is the only native venomous snake. Systemic features can occur in 30% of cases.

Local envenoming occurs within 30 minutes of the bite. There may be a tingling sensation, with local swelling surrounding the bite. This can spread to involve lymph nodes. Wider swelling may occur within 24 hours. In severe cases there is widespread extravasation which can cause shock.

Systemic envenoming causes acute anaphylaxis-type features which can persist for 48 hours. There is potential for severe effects in most organs e.g. cerebral oedema, cardiac arrythmias, acute pancreatitis.

In such patients, tourniquets and local compression have no benefit and may cause harm.

In the UK any patients with severe reactions should be discussed with the National Poisons Information Service. Any patient with envenoming or severe limb swelling should receive Viper antivenom.

Fig. 7 – Picture of an Adder – Image by Mick E. Talbot via Wikimedia Commons 

Summary

In summary, the causes of bites are varied in the UK. For isolated bites without concern of allergy or infection, these are usually best managed symptomatically. Lyme disease is a great mimic and sometimes the characteristic bullseye is missed or was never present. Lastly for suspected envenomation, NPIS/TOXBASE is a great resource to discuss the best management for these potentially very unwell patients.

References

1. National Institute for Health and Care Excellence (NICE). Insect bites and stings. CKS NICE, 2025.
2. National Institute for Health and Care Excellence (NICE). Lyme disease. CKS NICE, 2024.
3. GPnotebook. Adder bites or bite: treatment [Internet]. Last reviewed 4 Nov 2020.
4. Dermnet NZ, dermatology website.