This is particularly common in young gerbils just passed weaning and elderly gerbils when the weather is abnormally cold or hot. Prompt antibiotic treatment is essential. In the UK this has to be prescribed by a vet. I prefer an injection rather than drops in the water or food, as it is easier to ensure the correct dosage. However, this will mean you have to visit the surgery for 3 to 5 days for treatment.
All gerbils have a scent gland in the middle of their tummy.
This is long, thin and yellow in colour. It is sometimes mistaken for a wound or tumour. Gerbils mark their territory by rubbing their scent gland on it. Male gerbils kept with other males are particularly prone to scent gland tumours. Excessive marking of territory causes the tumour.