An ultra-Orthodox Jewish circumcision ritual is reportedly causing herpes among young infants in New York.

Herpes, a viral, contagious disease, is being found among baby boys exposed to a circumcision ritual whereby the circumcision wound is cleaned is cleaned orally, according to the New York Daily News.

There are said to have been six cases of infant herpes tied to the ritual since February 2015, including one where a baby boy was rushed to hospital 14 days after being subjected to the procedure.

The New York health department issued a warning to medical officials on Wednesday reporting the news. It said the boy was suffering from a rash that had spread across his genitals, buttocks, inner thighs and ankle.

The ritual is known as metzitzah b'peh, and involves the circumciser – known as the 'mohel' – sucking the blood from the circumcision wound with his mouth. Most Jewish families do not practise the ritual, but in New York City, approximately 3,000 babies are circumcised according to metzitzah b'peh every year.

New York mayor Bill de Blasio, responding to Wednesday's news, said: 'We're right now in that process of identifying the mohel [who performed the procedure], and we expect full cooperation from the community.'

A deal made by the de Blasio administration with Jewish leaders was meant to have involved the identification and isolation of any responsible mohels. However, of the six cases since 2015, only two of the rabbis involved have been named.

Altogether, since 2000 there have been 24 cases of infant herpes linked to circumcision, according to the New York Post. Two babies have died and two have suffered brain damage. The disease is more serious in infants as their immune systems have not developed.

Orthodox rabbis have resisted restrictions on the practise. De Blasio had wanted to make parents sign a consent form but withdrew