An undiagnosed disease that has affected 200 and left at least four dead in Cacuaco, about 20km north of the Angolan capital, Luanda, has health organisations scrambling to identify the illness.

The first cases were reported in early October. "What we know is that new cases keep arriving at the hospital," Balbina Felix, disease control officer at the World Health Organisation (WHO) in Luanda, told IRIN.

According to the Municipal Hospital in Cacuaco, 20 new cases per day have been reported since Monday, with symptoms that include weakness, drowsiness, muscular spasms, a confused state of mind, dizziness and difficulty to walk and speak. Approximately 208,000 people live in the coastal municipality.

Felix described the illness as a "clinical neurological disorder", and dismissed fever or cholera as possible culprits, but health organisations are still in the dark. Identifying the disease has become a priority, to help prevent further transmission and treat fatally ill patients.

On Monday, a delegation comprised of Health ministry officials, Cacuaco municipal officials, and representatives of WHO, the US-based Centre for Disease Control (CDC) and the Angolan military health services visited affected areas.

Over 2,700 Angolans succumbed to cholera in 2006, and the waterborne disease has already killed over 400 people this year. In 2005 the country experienced the largest-ever recorded outbreak of Marburg haemorrhagic fever, a rare but fatal disease caused by a virus from the same family as the Ebola virus.

A WHO statement released on Tuesday said the organisation had deployed "an international team of experts in clinical toxicology, epidemiology and environmental health, as well as laboratory personnel, to assist the Ministry of Health in the ongoing investigation" and "experts from the Centres for Disease Control (CDC), based in Luanda, have also offered support for the investigation."

The teams would "support the Ministry of Health ... provide advice on case- and risk-management, and identify laboratories for analysis of human and environmental samples to investigate the cause and the source of the disease". According to Felix, samples have already been sent to the CDC in Atlanta, US, and to testing facilities in France, the UK and Germany.

The Ministry of Health has advised the population to observe individual and collective measures, particularly related to hygiene, to avoid risk and report to the nearest health facility at the first sign of illness.