MEDECINS Sans Frontieres (MSF) in Hong Kong has issued an urgent appeal for antibiotics to combat dysentery - the illness now posing the most serious risk to masses of Rwandan refugees. Spokesman Fiona MacMahon said nalidixic acid or Negram was the best treatment for dysentery, and urged pharmacists with spare supplies to contact the organisation. Cases of dysentery have now overtaken new outbreaks of cholera in the overcrowded refugee camps. A five-day course of antibiotics is needed to treat it. MSF around the world is also calling for hundreds of human rights observers to be sent to Rwanda. Governments are being asked for their support and in a letter sent to Hong Kong Governor Chris Patten, MSF said refugees would not return to Rwanda if their security could not be guaranteed. It is understood six observers will be sent but MSF told Mr Patten that number is derisory and asked him to support proposals to send as many as 600. The Hong Kong Joint Appeal for Rwanda is now in its second successful week. By Tuesday more than $6.1 million had been raised for MSF, the Red Cross and Oxfam. Oxfam is now distributing fresh water daily to more than half a million people, but aid workers need about 80 water tankers to overcome transport problems and reach Oxfam's goal of 800,000 people per day. A two-week appeal began at the Excelsior Hotel in Causeway Bay yesterday with guests and staff asked to make donations. Hotel guest Juergen Dieter Voss, a businessman from Bangkok, deposited one of the first donations - an envelope containing a secret amount.