Several European countries face a growing scare over millions of eggs that have been contaminated with the insecticide fipronil, which is potentially harmful to humans.

Here is what we know so far about the latest food safety scandal to hit the continent in recent years:

- When it started -

Belgium has admitted that it knew about fipronil in eggs in early June but kept it secret because of a fraud investigation.

Belgium officially notified the EU's food safety alert system on July 20, followed by the Netherlands on July 26 and Germany on July 31.

National authorities did not make it public until August 1.

- Affected countries -

The Netherlands was the epicentre of the problem and the first to act, ordering eggs pulled from supermarket shelves and urging shoppers to throw theirs away.

Dutch authorities have temporarily closed 138 poultry farms and may cull millions of chickens.

Belgium has blocked products from 57 egg producers and several supermarkets have withdrawn affected eggs.

German authorities blocked the distribution of thousands of eggs while supermarket chain Aldi pulled all Dutch eggs from its German stores.

Sweden, Switzerland, Britain and France have also said that they have found small quantities of fipronil-tainted eggs.

- How it started -

The problem is believed to stem from a substance used by a Dutch company, Chickfriend, that farmers say in the Netherlands and Belgium say they hired to treat their chickens.

A lawyer for a Belgian company, Poultry-Vision, says the firm sold it to Chickfriend but has not said where it got the substance. Media reports have said it may have come from Romania.

The French government says a Belgian company -- which it did not identify -- mixed fipronil with another lawful substance.

- Investigation -

Criminal probes for suspected fraud are under way in Belgium and the Netherlands.

Germany has pushed the Belgian and Dutch authorities to quickly clear up the situation and said there was "criminal intent".

The European Commission meanwhile said any countries that were found not to have notified Brussels immediately about the detection of fipronil could face legal action.

- Fipronil -

Fipronil is a pesticide used to treat the parasite red lice, which is common in poultry, and to de-flea household pets like dogs and cats.

But it is banned from being used to treat animals destined for human consumption such as chickens.

In large quantities, fipronil is considered to be "moderately hazardous" according to the World Health Organisation, and can have dangerous effects on people's kidneys, liver and thyroid glands.

EU rules say eggs with a level of fipronil above 0.005 mg per kg must be withdrawn from the market. Fipronil levels above 0.72 mg per kg represent a possible acute health risk, the EU says.

Source: AFP