Scientists find new superbug strain of salmonella

* Experts call for better surveillance to limit international spread

* Poultry appears to be major vehicle for spreading this strain

* Separate outbreak of salmonella in U.S. kills one, sickens 77

LONDON, Aug 3 (Reuters) - Scientists have identified an emerging "superbug" strain of salmonella that is highly resistant to the antibiotic Ciprofloxacin, or Cipro, often used for severe salmonella infections, and say they fear it may spread around the world.

The strain, known as S. Kentucky, has spread internationally with almost 500 cases found in France, Denmark, England and Wales in the period between 2002 and 2008, according a study in the Journal of Infectious Diseases.

French researchers who led the study also looked at data from North America and said reports of infection in Canada and contamination of imported foods in the United States suggest the strain has also reached there.

The study was published on Wednesday as U.S. health officials reported a multi-state outbreak of another strain of antibiotic-resistant salmonella -- called S. Heidelberg -- which has so far made 77 people sick and killed one.

Salmonella infection is a major public health problem worldwide. There are an estimated 1.7 million infections in North America each year and more than 1.6 million cases were reported between 1999 and 2008 in 27 European countries.

Although most salmonella infections produce only mild gastroenteritis with stomach cramps, fever and diarrhoea, older people or those with weaker immune systems are particularly at risk of life-threatening infections.