Between January and June 2015, seven cases of the sexually transmitted disease were reported in the two counties. That figure rose to 23 cases between July and December, and 21 cases from January to June this year.

The HSE’s department of public health in Cork said eight in ten reported cases were among men who have sex with men. It advised all sexually active men who have or had sex with men, and women whose partners have sex with men, to get tested for STIs and always use a condom during sex.

If not treated promptly and with the correct antibiotics, the infection can cause long-term serious problems, including the possibility of damage to the heart and brain.

The HSE said the first symptom, primary syphilis, is usually the appearance of a painless sore at the location where the infection entered the body.

The HSE said: “Syphilis has been called the ‘great pretender’ as its symptoms can look like many other diseases. Up to half of people with syphilis may not notice any symptoms; therefore it is vital to get tested.”

Dr Aileen Kitching, consultant in public health medicine at the Department of Public Health in Cork, said: “The cases we are seeing are mostly in men who have sex with men, with over half of male cases in older adult age groups, over 35 years of age. Around one in five of these cases have had one or more other STIs.

“Increased public awareness about STIs, including signs and symptoms and where you can get tested, is essential.

“Having syphilis once does not protect a person from becoming infected again. Even following successful treatment, people can be reinfected.”

Professor Mary Horgan, consultant in infectious diseases at Cork University Hospital and clinical lead for STI services in Cork and Kerry, said: “I would encourage [men who have sex with men and] who have had unprotected sex, including unprotected oral sex, to book an STI test as soon as possible. The earlier we diagnose and treat, the better.

“As syphilis can take up to 90 days to show up on a blood test, we encourage routine twice yearly testing for all sexually active MSM, as part of regular STI screening.”

Free STI testing is available in the Cork STI clinic at South Infirmary Victoria Hospital. It also provides outreach clinics in Kerry General Hospital. For more information, call 021 4966844.