Human plague in the United States.
To the Editor:— The Aug 5, 1962 issue ofThe Journalcarried a cover picture of a painting by Arnold Bocklin entitled "Plague" and an article entitled "Human Plague in the United States" by Caten and Kartman. This article and the caption next to the cover picture carry misleading statements which I would like to call to your attention. Discussing the distribution of wild-rodent plague in the United States, Caten and Kartman state, "The reason why plague does not extend beyond the 100th meridian is poorly understood." While it is true that all human cases associated with wild rodents for which adequate data are available have been acquired west of the 100th meridian, and this corresponds quite well to the known distribution of wild-rodent plague, as shown by Caten and Kartman, very limited surveys of wild rodents and fleas for plague have been conducted east of the 100th meridian. 1 Many investigators believe that wild-rodent plague does not extend into the eastern states, largely on the basis of the distribution of human cases associated with wild rodents. On the other hand, plague-infected wild rodents or their ectoparasites have been identified from over 130 counties in the western
Plasmids and pestilence--biological and clinical aspects of bubonic plague.
These discussions are selected from the weekly staff conferences in the Department of Medicine, University of California, San Francisco. Taken from transcriptions, they are prepared by Drs Homer A. Boushey, Associate Professor of Medicine, and David G. Warnock, Associate Professor of Medicine, under the direction of Dr Lloyd H. Smith, Jr, Professor of Medicine and Associate Dean in the School of Medicine. Requests for reprints should be sent to the Department ofMedicine, University of California, San Francisco, School ofMedicine, San Francisco, CA 94143.
Lake Muzahi, Rwanda: limnological features and phytoplankton production
Lake Muhazi, a small lake of Rwanda (East Africa) was studied from 1986 to 1990. A dramatic decrease of the catch of Oreochromis niloticus (350 T y−1 in the fifties vs 30 T y−1 in 1982) suggested a loss of productivity or overfishing. In the same period, other ecological changes occurred: the submerged macrophytes regressed and there was a decrease in Secchi depth (0.65 m in 1987 vs 1.5 m in the fifties). Compared to other lakes of the same area, the plankton production seemed low. The results of the present study characterize lake Muhazi as a shallow lake with a rather unstable diurnal stratification and with slight differences in mixing regime between its eastern, deepest part and its western, shallowest part. Secchi disk depth does not vary seasonally to a large extent. The water has a rather high mineral content (conductivity of about 500 µS cm−1 at 25 °C) and low concentrations of dissolved N and P, except in the hypolimnion, where NHinf4sup+-N can be high.Two species, Microcystis aeruginosa and Ceratium hirundinella, account for most of the phytoplankton biomass, which is about 50–80 mg chlorophyll a m−2 in the euphotic zone, usually with little seasonal variation. Daily gross production estimates amount to about 6 to 9.5 g O2 m−2 d−1 with a significant difference between the two parts of the lake. Data on C:N and C:P ratio in the phytoplankton suggest that some N deficiency might occur in the eastern part. Moreover, the Zm:Zc ratio could also lead to rather low net production rates (0.21–0.25 d−1 for a mixed layer of 4 m)In conclusion, the primary production of lake Muhazi is medium for African lakes and the hypothesis that decreased planktonic production could account for a reduced fish production should be discarded. Whereas the present yield of the fishery is only 20 kg ha−1 y−1, the yield estimated from primary production ranges between 46 and 64 kg ha−1 y−1. This could be reached through proper management. Finally, some hypotheses are given to explain the ecological changes which occurred in the lake.