An epidemic of louse-borne relapsing fever in Kenya

Abstract

Summary 1. An epidemic of relapsing fever involving the hinterland of Mombasa and the Kenya Coast is described. 2. There were nearly 2,000 cases, with a 40 per cent, mortality in untreated cases. 3. Control measures rapidly terminated the epidemic. About 100,000 people were disinfested with 5 per cent, DDT powder. Various administrative steps (such as abolition of funeral ceremonies, prevention of travel, etc.) were also important in the control of the spread of the disease. 4. Clinically, cases were characterized by the prominence of neurological symptoms, cardiac involvement, positive Weil-Felix reactions and negative Kahns. 5. The disease was introduced from Arabia and was of louse-borne origin. Infected lice were recovered from patients and the disease was transmitted from these lice to monkeys. There was no evidence incriminating other possible vectors and the spirochaete was found to be non-transmissible by the ticks O. moubata and savignyi . 6. The behaviour of the spirochaete in different animals was observed and compared with that of S. duttoni . Rabbits, guineapigs, bush-babies, white rats, white mice, gerbilles and monkeys were found capable of being infected, their relative susceptibility being in the order shown, with rabbits the least and mice and monkeys the most susceptible. The following observations are particularly to be noted:— (i) Repeated passage in mice was easily maintained. (ii) Neurotropism occurred in S. duttoni infections in mice, but scarcely ever in recurrentis . (iii) Relapses of S. recurrentis occurred in 69 per cent. of monkeys, the interval between the relapses being 10 to 12 days. Relapses tended to be more severe than the original attack. (iv) S. duttoni infections differed from recurrentis in being much more fatal in monkeys and much more persistent in rats and white mice. 7. The infections in lice showed a well-marked negative phase lasting till the 16th day; lice collected from patients and examined within 24 hours never showed spirochaetes. 8. No cross immunity exists in animals (except bush-babies) between S. recurrentis and S. duttoni . There was cross immunity in two out of three monkeys tested against a relapse strain. 9. Auto-agglutination of spirochaetes in old infections (primary attacks) occurs in monkeys but not in rats. 10. Some evidence was produced to show the immunizing effect of killed spirochaetes. 11. The pathogenicity of the Kenya spirochaete in man and animals resembles most closely that of S. carteri and differs markedly from the Chinese and Abyssinian strains. 12. It is suggested that the louse-borne spirochaetes may be divided into two groups. The first exhibits a long negative phase in the louse (European, North African and Kenya strains); the second never shows this phase and spirochaetes are present throughout the louse cycle (Abyssinian and Chinese strains). 13. The pathological changes resembled those previously described except that in three instances degeneration of ganglion cells was found in the cerebellum without meningovascular inflammation.