A polio immunisation campaign is being launched across five districts in northern and northeastern Kenya, after a child in a refugee camp was diagnosed with the paralysing disease, health ministry officials said on Friday.

A total of 250,000 children are to be targeted after the three-year-old Somali girl was found to have polio on 13 October despite having undergone all the necessary vaccinations, the ministry added.

The case, at Hagadera camp, one of three refugee settlements in Daadab, is the first to be reported in Kenya since 1984.

Two more cases of suspected polio are being investigated, according to Tatu Kamau, the manager of the ministry of health's Expanded Programme on Immunisation.

The five-day campaign will start on Saturday in the districts of Moyale in the north, Garissa, Ijara and Wajir in the east, and Mandera in the northeast. All children under the age of five years will be vaccinated against polio.

As a result of the 2003-2005 polio outbreaks in west and central Africa, the illness spread to 16 countries previously free of the disease: Benin, Botswana, Burkina Faso, Cameroon, Central African Republic, Chad, Côte d'Ivoire, Ethiopia, Ghana, Guinea, Indonesia, Mali, Saudi Arabia, Sudan, Togo and Yemen.

Poliomyelitis ("polio") is caused by the poliovirus, which enters the body orally, infecting the intestinal lining. It may then enter the blood stream and the central nervous system, causing muscle weakness and often paralysis.

In areas with poor hygiene and sanitation, polio spreads through human contact, usually by faecally-contaminated water or food, but the virus can also be spread through coughing and sneezing in crowded environments.

Symptoms include fatigue, sore throat, fever, vomiting, gastro-intestinal disturbances, headache and pain in the neck and extremities. Weakness of muscles often leads to permanent paralysis and deformity of the limbs.