1955 North of England outbreak

In 1955, an extensive outbreak of myalgic encephalomyelitis in the North of England in 1955 was recorded. It primarily struck primary school children starting in February and spread to the adults in March and April. By July, 233 cases had been recorded. The male: female ratio was 1:1. Twenty children boarding at the Carlisle Corporation Home, Dalston, mainly boys aged 5 to 15 years, were all affected. Secondary attacks in contacts occurred in several families after a primary host relapsed, suggesting that the patient had again become infectious.

Symptoms included:
 * swollen, tender lymph nodes, liver and spleen
 * marked fatigability
 * impairment of memory and concentration
 * changes of mood with behavior disorders in children
 * sleep disorders
 * irritability or depression
 * involvement of the autonomic nervous system resulting in orthostatic tachycardia, coldness of the extremities, episodes of sweating or profound pallor, sluggish pupillary responses, constipation and frequency of micturition, possibly as the result of a hypothalamic disturbance
 * diffuse and variable involvement of the nervous system leading to ataxia, weakness or sensory changes in a limb, nerve root or a peripheral nerve distribution, especially involving the ulnar nerve
 * muscle pain, tenderness and myasthenia
 * recurrences in about 20% of patients over a period of several years.

Also observed were morphological changes in the lymphocytes with relative lymphocytosis and eosinophilia. In some cases the abnormal blood films persisted for at least 18 months. In most of the Dalston cases the onset was abrupt after an incubation period of 5 to 7 days, but some of the adults showed a delayed onset with the illness reaching the maximum severity after 6 weeks. Neurological symptoms occurred in 60% of the patients, but objective changes were mild and seen only in 20% of cases. There were ulnar nerve lesions in eight patients. Non-specific abnormalities were noted in the EEGs in fifteen of the twenty-three patients tested. The CSF was normal in the few examinations made. Virus studies were also negative. The case incidence and percentage of neurological involvement were similar to that observed in the Swiss military epidemics.