Primary herpetic gingivostomatitis: mouth sores with a fever in a child

MSD Manuals writes that a first HSV infection in the mouth usually causes many painful sores inside the mouth, that this picture is called herpetic gingivostomatitis, and that it develops most often in children. The person usually feels ill, with fever, headache and body aches. A 2023 systematic review states that 13 to 30 per cent of first HSV-1 infections turn into this picture, while the rest pass more mildly or without symptoms. So a child's first meeting with the virus usually goes unnoticed; what gets noticed is this severe form.

The most distinctive feature of the picture is the gums. In mouth ulcers and many other mouth sores the gums stay healthy, whereas here the gum margin turns red all the way along, swells and bleeds easily. According to MSD's professional section, small fluid-filled blisters appear inside the mouth and on the gums, and these usually burst within a few hours to 1–2 days and turn into sores. That is why parents usually see not the blisters but sores with a yellowish-white base and red edges, merging in places. There may also be blisters and crusts on the lips and the skin around the mouth.

On duration, MSD's two sections use different wording: the section written for the public says the mouth sores last 10 to 19 days and are often severe enough to make eating and drinking very uncomfortable, while the section written for doctors says the first infection usually heals within 2–3 weeks of onset. In practice, this means the fever and the worst pain come in the first days, while the sores can last more than two weeks. Knowing this time frame matters so that you do not panic because it has not cleared up within a few days, but do keep track of fluid intake every day.

The real danger is fluid loss. MSD writes that difficulty eating and drinking can lead to the body becoming short of water (dehydration); the 2023 review also states that this picture sometimes requires admission to hospital. A young child may refuse even water because of the pain. The NHS lists the signs of dehydration as dark yellow, strong-smelling pee, peeing less often, and a dry mouth, lips and tongue; and in babies, a sunken soft spot on top of the head (fontanelle), sunken eyes, few or no tears when crying, fewer wet nappies and being drowsy or irritable.

Where antiviral medicine fits depends on timing. In a randomised, placebo-controlled study published in the BMJ in 1997, involving 72 children aged 1–6, children whose symptoms had been present for less than 72 hours were given aciclovir by mouth for 7 days. In the children taking aciclovir, the mouth sores cleared in a median of 4 days, compared with 10 days in those taking a placebo; fever resolved in 1 versus 3 days, difficulty eating in 4 versus 7 days, difficulty drinking in 3 versus 6 days, and virus shedding ended in 1 versus 5 days. This is the key study showing that the medicine works when started in the first three days.

Even so, the body of evidence is limited. The 2023 systematic review writes that only one of five studies could offer weak evidence that aciclovir is effective, and that most of the treatments recommended are symptom remedies that have no effect on the virus and were settled on by trial and error. An important finding of the review is this: diagnosis is often delayed by about 72 hours, and this delay reduces the effect of any antiviral. So when you suspect this picture, seeing a doctor in the first days increases the chance that the medicine will work.

The picture is not limited to children. In a series of 13 adult cases published in the Journal of the Canadian Dental Association, the patients were aged between 18 and 79; in young adults, fever and swollen lymph glands were as in children, while in older patients the symptoms were more confined to the inside of the mouth. The authors stress that the dentist is often the first health professional these patients turn to, and that the diagnosis is especially important in older people and in people with weakened immunity.

After the first infection passes, the virus is not cleared from the body; it stays quietly in a nerve ganglion. Later, it can come back as a cold sore on the lip with triggers such as stress, sun or an illness with a fever. These recurrences are usually much milder, and the severe picture affecting the gums usually does not recur. Managing cold sores is a separate subject and is explained on our cold sores page.

The first list gives signs suggesting herpetic gingivostomatitis. The second list gives signs suggesting either another illness or a situation that cannot wait. The doctor makes the definite diagnosis by examination and, if needed, with a sample taken from a sore.

The order is first to assess for an emergency and fluid loss, then to make the diagnosis, and last of all to decide on antiviral and pain treatment.

1. 1

   Emergency signs first

   If there is difficulty breathing or very fast breathing, blue, grey, pale or blotchy skin, lips or tongue, cold skin, being hard to wake, being very sleepy or confused, pain on looking at light with a red eye, the eye being very dark red or the pupils being unequal, the assessment is done at A&E; call 112.

2. 2

   Assessing fluid status

   The doctor asks how much the child is drinking, how often they pee or how many wet nappies there are, about dryness of the mouth and lips, and about their general condition. If not enough fluid can be taken by mouth, admission to hospital for fluids through a drip may be needed.

3. 3

   Diagnosis

   MSD writes that the diagnosis is usually made from the appearance of the typical sores, and that if needed, the virus is looked for in a sample taken from a sore with culture, PCR or an antigen test. At this stage the doctor tells it apart from mouth ulcers, hand, foot and mouth disease and other mouth sores.

4. 4

   The antiviral decision

   MSD writes that in severe cases aciclovir, valaciclovir or famciclovir can be used by mouth. In the randomised study in children, when aciclovir was started within the first 3 days, the duration of the sores, the fever and the difficulty eating and drinking was shortened. Tell the doctor the day the symptoms started; the doctor sets the dose and length of the medicine.

5. 5

   Pain control and fluids

   MSD states that numbing medicines applied inside the mouth can ease symptoms. Ask your doctor or pharmacist about the type and dose of painkiller and fever reducer. Cold water, cold milk, yoghurt and mashed soft foods are usually accepted more easily; acidic, salty and spicy foods sting the sores.

6. 6

   Preventing spread

   Until the sores have fully healed, kissing and sharing cups and cutlery are avoided, and hands are washed after touching the sores. The NHS advises trying to discourage children who have caught a finger infection (herpetic whitlow) from sucking their fingers.

There are several common conditions that come with sores in the mouth. The differences below give clues; the doctor makes the distinction.

The following are wrong decisions that families, and sometimes doctors, often make, and what they cost.

Timings vary from child to child. The sequence below is the usual course described by MSD and the randomised study in children; the plan of the doctor following you takes priority.

1. The first days

   Fever, tiredness, irritability and loss of appetite; the gums turn red and swell, and blisters burst within a few hours to 1–2 days and turn into sores. This is the most valuable period for antivirals.

2. The first week

   Pain and difficulty eating and drinking are at their most marked. In the study, in untreated children, difficulty drinking lasted a median of 6 days and difficulty eating 7 days. Keep a close eye on fluid intake.

3. The second week and after

   The sores gradually get smaller. According to MSD, mouth sores can last 10–19 days, and the first infection usually heals within 2–3 weeks.

4. After healing

   The virus stays quietly in the body; it may come back later as a cold sore on the lip. These recurrences are usually much milder.

We do not give a figure here; managing this picture is more the area of the GP (family doctor) and the paediatrician than of the dentist, and its scope varies with how severe the illness is. The main factors that determine the scope:

When the diagnosis is made

If you seek help in the first days, the option of antiviral treatment stays open and the illness may be shorter.

The degree of fluid loss

If not enough fluid can be taken by mouth, fluid treatment through a drip in hospital may be needed.

Complications

If the eye, eczema skin or a finger is affected, a specialist examination and further treatment are needed.