TRANSACXONS OF THE ROYAL SOCIETY OF TROPICAL MEDKINE AND HYGIENE (1985) 79, GXRESPONDENCB 139 Table I-G-values calculated from the data of TIBAYRENC et al. (1984) and their sipiiicance Suburb Sum-G Total-G Tupiza A: zona BOliV&U Villa Remedios 1.48 (1~ooo) 12.36 (0.223) 1 13.84 (0.223) Tupiza B: suypaclls 6.73 (O-410) Suycuchacra 19.13 (0.067) Tocloca 13.94 Pow Chacoparnpa 13.86 (0.877) Palquixa 6.11 (O-453) 59.77 (0.035) Tarija: Degc; de1 Tomatitas 12.50 (0340) I 17.68 (0.026) 5.18 (0.790) 91.29 (0.002) correlation exists with environmental factors (e.g., altitude). Slrnilar problems are encountered when xymodeme frequencies are used to make inferences concerning the sexuality of T. cruai. Deviation8 from Hardy-Weinberg expectations must be interpreted with some caution. It is difficult, in any case, to see how a concept of random mating could apply to T. cruzi given its microdistribution. Opportunities for genetic exchange between certain xymodemes’ are limit+ and if sex is only an occasional event the di;;;mutmn of recombmants may be severely res- Financial support from the MRC and UNDP/ TVA! Bank/WHO Special Programme is acknow- R. E. CIBIJLSKIS Dept. of Medical Protoaoology, London School of Hygiene and Tropical Medicine, Keppel Street, London, WCIE 7HT. References Lehane, M. J. & Schofield, C. J. (1981). Field experiments of dispersive flight by Triutoma infestmu. Transactions of the Royal Society of Tropical Medicine and Hygiene, 75, 399-400. Marsden, P. D., Virgens, D., Magalhaes, I., Tavares-Neto, J., Ferreira, R., Costa, C. H., Castro, C. N., Macedo, V. & Prata, A. (1982). Ecologica domestica do Triatoma infestans en Mambaf, Goi&-Brasil. Revista do Institute de Medicina Tropical de Scio Paulo, 24, 364-373. Miles, M. A. (1979). Transmission cycles and the heter- ogeneity of Ttypanosoma cmzi. In: Biology of the Kineto- phrrida. Vol. 2, Lumsden,W. H. R. & Evans, D. A. (Editors), London: Academic Press, pp. 117-l%. Miles, M. A., Toye, P. J., Oswald, S. C. & Godfrey, D. G. (1977). The identification of two distinct strain-groups of Typanosoma cruzi circulating independently in a rural area of Brazil. Trmactions of the Royal Society of Tropical Medicine and Hygiene, 71, 217-225. Miles, M. A., Cedillos, R. A., P6voa, M. M., Souza, A. A. de, Prata, A. & Macedo, V. (1981). Do radically dissimilar T~atwxnna cruzi strains (zymodemes) muse Venezuelan and Bmzilian forms of Chagas’ disease? Luncet, i, 1338-1340. Sok$, RHRF: Rohlf,~.~(l;~~).,. San Francisco: Tibayrenc, Mzalar, L:: Dujardin, J P., Poch, P. & Desjeux, P. (1984). The microdistribution of isoenzymic strains of Ttypanosoma cnui in southern Bolivia; new isoenzyme profiles and further arguments against Mendelian sexuality. Transactions of the Rqal Society of Tropical Medicine and Hygiene, 78, 519-525. Accepted for publication 21st September, 1984. Relapse of Israeli spotted fever treated with doxycycline Spotted fever is a rubric given to a variety of tick-borne rickettsial disease throughout the world. Like Boutonneuse fever, Israeli spotted fever gener- ally follows a milder clinical course than Rocky Mountain spotted fever (GUTMAN, 1978). However, an es&r at the site of the tick attachment, which a P pears with considerable regularity in Boutonneuse ever, is seldom if ever reported in the diseaseas it occurs in Israel (GROSS et al., 1984). According to the current literature, in cases of illness due to spotted fever, antibiotic therapy should be administered until the patient has improved and has been afebrile for 24 hours (WOODWARD, 1983). Cases of Rocky Mountain spotted fever treated for five to seven days may relapse if the treatment was hegun early in the course of the disease (C. L. Wisseman, Jr., personal communication). We wish to report a case of relapseof Israeli spotted fever in a child treated with doxycycline according to the recommendation mentioned above. A two-year-old male was admitted to the Soroka Medical Center with a two-day history of fever. On admission, a temperature of 39X, a macular rash accentuated on the limbs including pahns and soles, and generalixed lymphadenopathy were recorded. Oral doxycycline was given at a dosageof 2.2 mg/kg twice daily for the first day and 1.1 mg/kg twice daily on subsequent days. The temperature returned to normal after five doses of doxycyline. Treatment continued for an additional 24 hours. Following cessation of antibiotic therapy for one day he became febrile and lethargic. Leucopenia, thrombocytopenia and hyponatraemia were found. Doxycycline therapy was restarted according to the previously mentioned schedule. The fever resolved, the child was continued on doxycycline therapy for one week. Recovery was uneventful. At a 140 dilution, serum taken on admission to hospital was negative, using the immtmofluorescent