An urgent investigation is under way to understand how and where four patients have caught monkeypox in England.

Describing the incidents as 'rare and unusual' medics - who have found no links to travel or African countries where the virus is endemic - say early signs now suggest there could be some transmission of the virus in the community.

With seven confirmed cases now in the UK since early May, and the UK Health Security Agency in a race to find the source of the latest outbreak, we take a look at what monkeypox is and why has its arrival in Britain got health officials worried?

What is monkeypox?

Monkeypox, which comes from the same family of viruses as small pox, is a viral infection usually associated with travel to West Africa. There are two strains of the virus - West African and Central African - with the latter being the more severe.

The virus attacks the lymph nodes.

It can be caught from infected wild animals if you're bitten or touch their blood or bodily fluids or by eating meat from an infected animal that hasn't been cooked properly. Human to human transmission, says the NHS, is ordinarily rare.

Monkeypox is usually a mild self-limiting illness, spread by very close contact with someone with monkeypox and most people go on to recover within a few weeks. But it can take between five and 21 days for an infection to appear, which means there is a risk people can unknowingly spread the infection before they realise they are ill.

What are the symptoms?

Initial symptoms of monkeypox include fever, headache, muscle aches, backache, swollen lymph nodes, chills and exhaustion. A rash can develop, often beginning on the face, then spreading to other parts of the body including the genitals.

The rash changes and goes through different stages, and can look like chickenpox or syphilis, before finally forming a scab, which later falls off.

How is it spread?

Monkeypox does not spread easily, say health experts, but it can be passed from person to person if there is close contact.

You can spread and catch monkeypox by sharing towels or bedding with someone who has the infection, by touching skin or blisters infected with monkeypox or by inhaling the coughs or sneezes of someone with the monkeypox virus.

How many cases are there in the UK?

There are now seven confirmed cases of monkeypox in the UK, diagnosed between May 6 and May 15.

Four of those have been identified this week with no known connections to the three previous patients discovered earlier this month and who did have some links and travel connections to Africa.

Three of the four new cases have links to London, and one to the north east, however early investigations indicate that all four were most likely infected in the capital but common contacts have only been identified in two out of the four most recent cases.

Why are health officials concerned?

The latest four cases take the total number of monkeypox cases in this country to seven.

But what is most concerning is that none of the latest four have a link to travel to a country where monkeypox is endemic, and they also don't seem to be connected to the earlier cases, which is concerning for health officials who now admit this could be a sign of transmission happening in the community.

The UKHSA has launched an urgent investigation to try and understand where the four individuals may have acquired their infections, and to establish whether there could be more people infected.

Are the patients in hospital?

Those patients needing medical care are all in specialist infectious disease units at the Royal Free Hosptial, Royal Victoria Infirmary in Newcastle upon Tyne and Guys’ and St Thomas’, the UK Health Security Agency has confirmed.

The individuals infected with monkeypox have what is known as the West African clade of the virus, which is milder compared to the Central African clade.

What's the advice to people?

The UKHSA, while admitting the latest developments are concerning, insists the risk to the wider public does remain low.

All four of the newest cases self-identify as gay, bisexual or other men who have sex with men, (MSM) says the UKHSA, which is trying to establish whether the four have any possible links to each other.

Due to the recent increase in cases and uncertainties around where some of the individuals have acquired the infection the UKHSA says it is now working with the NHS to identify if there may have been any other suspected cases in recent weeks, particularly in and around the capital, as well as speaking to other countries to find out if they are noticing any similar rises in monkeypox cases.

Because the most recent cases are in gay, bisexual and other MSM communities, and as the virus spreads through close contact, the UKHSA says it is advising people in these groups to be alert to any unusual rashes or lesions that may appear on any parts of their body and to contact a sexual health service if they have concerns.

Anyone worried that they could be infected with monkeypox is advised to contact a clinic by phone before visiting in person, and every call or discussion will be treated sensitively and in confidence, it adds.

Dr Susan Hopkins, Chief Medical Adviser, UKHSA, said: "This is rare and unusual. UKHSA is rapidly investigating the source of these infections because the evidence suggests that there may be transmission of the monkeypox virus in the community, spread by close contact.

"We are particularly urging men who are gay and bisexual to be aware of any unusual rashes or lesions and to contact a sexual health service without delay.

"Clinicians should be alert to individuals presenting with rashes without a clear alternative diagnosis and should contact specialist services for advice."