The number of people living with multiple sclerosis around the world has increased by 10 percent in the past five years to 2.3 million, according to the most extensive survey of the disease to date.

The debilitating neurological condition, which affects twice as many women as men, is found in every region of the world, although prevalence rates vary widely.

Multiple sclerosis (MS) is most common in North America and Europe, at 140 and 108 cases per 100,000 respectively, while in sub-Saharan Africa the rate is just 2.1 per 100,000, the Multiple Sclerosis International Federation's Atlas of MS 2013 showed on Wednesday.

The atlas also confirmed that MS occurs significantly more in countries at high latitude, with Sweden having the highest rate in Europe and Argentina having more cases than countries further north in Latin America.

The reason for the link to high latitudes is unclear but some scientists have suggested that exposure to sunlight may reduce the incidence of the disease.

The survey found a big increases in the number of medical experts trained to diagnose MS and help patients with treatment, while the number of magnetic resonance imaging (MRI) machines available to carry out scans has doubled in emerging countries.

But huge disparities remain when it comes to access to modern disease-modifying drugs.

MS medicine has seen a number of advances in recent years, particularly with the introduction of a new generation of oral therapies such as Novartis' Gilenya, Biogen Idec's Tecfidera and Sanofi's Aubagio.

These medicines offer an effective alternative to older disease-modifying treatments that are given by injection.

The survey found that injectable drugs like Biogen's Avonex and Teva's Copaxone were partly or fully funded in 96 percent of high-income countries, while Gilenya was available in 76 percent.

However, none of these drugs was available under government programs in low-income countries.