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To test the hypothesis that native high-altitude residents have less beta-sympathetic and more parasympathetic tone than newcomers, we compared the effects of beta-sympathetic and parasympathetic blockade in 10 Tibetan and 9 Han acclimatized male residents of Lhasa, Tibet Autonomous Region, China (elevation 3,658 m). Each subject was studied during cycle ergometer exercise at 70, 132, and 191 W after placebo (normal saline), beta-sympathetic (propranolol, 0.2 mg/kg iv), or parasympathetic (atropine, 0.04 mg/kg iv) blockade in random order on different days. At rest, the fall in resting heart rate with propranolol and the rise with atropine were equal in Tibetan and Han subjects. During exercise, the fall in heart rate with propranolol relative to placebo values was greater in the Han than in the Tibetan group, whereas the rise in heart rate with atropine was greater in the Tibetans. Propranolol or atropine administration did not change minute ventilation per unit O2 consumption in either group. At the highest level of exercise on the placebo day, the Tibetans achieved a higher work load and level of O2 consumption than the Han subjects. Propranolol or atropine reduced O2 consumption and work load similarly in the two groups at the highest exercise level. The results supported our hypothesis that native Tibetan residents of high altitude exhibit more para-sympathetic and less beta-sympathetic tone during exercise. Neither relatively greater parasympathetic nor less sympathetic activation appeared implicated in the greater exercise capacity of Tibetans compared with that of acclimatized newcomer residents of high altitude.

Elevated pulmonary arterial pressure in high-altitude residents may be a maladaptive response to chronic hypoxia. If so, well-adapted populations would be expected to have pulmonary arterial pressures that are similar to sea-level values. Five normal male 22-yr-old lifelong residents of > or = 3,600 m who were of Tibetan descent were studied in Lhasa (3,658 m) at rest and during near-maximal upright ergometer exercise. We found that resting mean pulmonary arterial pressure [15 +/- 1 (SE) mmHg] and pulmonary vascular resistance (1.8 +/- 0.2 Wood units) were within sea-level norms and were little changed while subjects breathed a hypoxic gas mixture [arterial O2 pressure (PaO2) = 36 +/- 2 Torr]. Near-maximal exercise [87 +/- 13% maximal O2 uptake (VO2max)] increased cardiac output more than threefold to values of 18.3 +/- 1.2 l/min but did not elevate pulmonary vascular resistance. Breathing 100% O2 during near-maximal exercise did not reduce pulmonary arterial pressure or vascular resistance. We concluded that this small sample of healthy Tibetans with lifelong residence > or = 3,658 m had resting pulmonary arterial pressures that were normal by sea-level standards and exhibited minimal hypoxic pulmonary vasoconstriction, both at rest and during exercise. These findings are consistent with remarkable cardiac performance and high-altitude adaptation.

Microscopic examination of cultured human monocytes infected with Rickettsia sennetsu and stained by the Giemsa method revealed the presence of various organismal growth forms in the cytoplasm of the infected cells. The growth forms were loosely scattered individual organisms, clusters of organisms, various sizes of dense inclusion bodies in intact and vacuolated cytoplasm, and organisms in close proximity to disintegrated monocytes. The appearance and the morphology of these R. sennetsu growth forms were similar to those of Ehrlichia canis propagated in canine monocytes. Specific identification of R. sennetsu was made by staining cultured monocytes with fluorescein-conjugated globulins extracted from the pooled sera of patients recovering from sennetsu rickettsiosis. Mice infected with cultured R. sennetsu developed gross pathological changes indicative of infection, and the organism was demonstrated in their spleens, peritoneal macrophages, and mononuclear blood cells. Human monocyte culture appeared to be more sensitive than the previously used African green monkey kidney cell line (BSC-1) for the isolation of R. sennetsu from samples containing minute infectious quantities of this organism.

Leptotrombidium (Leptotrombidium) Arenicola (Traub, 1960) a probable vector of scrub typhus, is widely distributed along both E and W coasts of West Malaysia, the only country where this mite has so far been found. Distribution was determined by collection of unengorged larvae from the ground on black plates. Habitats had a variety of vegetational cover, but all had sandy soil and shade. Larvae were found in considerable numbers as far inland as 135 m (150 yards) from the edge of open sand; once larvae were found .8 km (1/2 mile) from the beach, but they were most numerous within 30 m (30 yds) of the shore. Distribution of larvae within typical habitats was very uneven and often larvae were absent. Frequently L. (L.) arenicola and L. (L.) deliense (Walch, 1922) were found together, but L. (L.) arenicola was never found in association with L. (L.) akamushi (Brumpt, 1910).

A RECENT report1 described the simultaneous occurrence of aseptic meningitis in a woman at term and fatal meningoencephalitis with myocarditis in her newborn infant. It is the purpose of this repor...

The life cycle of 5 generations of Leptotrombidium (L.) fletcheri infected with Rickettsia tsutsugamushi and reared under ambient temperatures in Malaysia was presented and compared with a colony reared at a constant 27 degrees C (Neal and Barnett, 1961). In general our colony had a longer generation time (average of 54 days from engorged larvae to adult compared with 37 days) and produced fewer eggs (average of 127.9 compared with 900.0) than the comparison colony. Possible factors causing these differences are discussed.

Ehrlichia sennetsu, the causative agent of human sennetsu rickettsiosis, was successfully propagated in primary canine blood monocyte cultures. The growth cycle of this organism appears to be similar to that of Ehrlichia canis. The antigen derived from our E. sennetsu cultures was used to develop an indirect fluorescent antibody test for detection and titration of serum antibodies to the organism. Using this test system, we found that five human serum samples obtained from patients clinically diagnosed as having sennetsu rickettsiosis were positive for anti-E. sennetsu antibodies. In addition, 29% of the serum samples obtained from 200 patients having a fever of unknown origin and residing in various regions of Malaysia were also serologically positive. All sera from apparently healthy individuals were negative in the test. Dogs inoculated with cell culture-adapted E. sennetsu developed a significant specific antibody titer to E. sennetsu, and the organism was subsequently isolated from their blood. These animals showed no clinical evidence of disease. The possibility of a higher prevalence of human sennetsu rickettsiosis in Southeast Asia and the potential usefulness of the canine model for studies of human sennetsu rickettsiosis are discussed.

Leptotrombidium (Leptotrombidium) arenicola Traub, a vector of scrub typhus, had previously been found to occur in the coastal vegetation behind the edge of open sand along the beaches of Peninsular Malaysia. Surveys of the west coast beaches of Sabah and Sarawak were conducted to determine if this species occurs in similar habitat in East Malaysia on the island of Borneo. Leptotrombidium (L.) arenicola was not collected from the eighteen sites studied. Of the 11,982 mite larvae collected, 55 per cent were L.(L.) deliense (Walch), a well-known, widespread vector of scrub typhus.

The transovarial development of Rickettsia tsutsugamushi in a colony of Leptotrombidium (Leptotrombidium) akamushi , a mite vector of scrub typhus, has been studied over 5 generations. The transovarial infection rate was 98%; the filial infection rate was usually 100%, though lower rates were occasionally observed. These rates may not be valid for all populations of vector mites because they have been estimated for female mites producing only female offspring. Nevertheless, these studies show that transovarial passage of rickettsiae can be highly efficient. By this mechanism, point foci of virtually 100% infected larval mites could be produced. The risk of infection for man exposed to larval mites in such point loci would be extremely high.

Leptotrombidium (L.) arenicola, described by Traub in 1960, has previously been shown to harbor Rickettsia tsutsugamushi , the causative agent of scrub typhus. In an attempt to establish the epidemiological importance of L. (L.) arenicola in the transmission of scrub typhus, studies of the behavior of R. tsutsugamushi in this vector were instituted. Transovarial transmission of R. tsutsugamushi through 2 generations of this trombiculid mite was demonstrated. In addition, these experiments showed that L. (L.) arenicola larvae can transmit scrub typhus rickettsiae during feeding on a mammalian host. Because L. (L.) arenicola is widely distributed along the sandy shorelines of both the eastern and western sides of the Malay peninsula. it is concluded that this vector may have considerable epidemiological importance in the transmission of scrub typhus.

The author describes his experience over the past 20 years in the Pentagon environment advocating greater understanding of the importance of human performance and its limits by military technologist. The human performance research community is a key player in the effort to reverse the present marginalization of the human in a technology-dominated world. The author suggests specific initiatives the community could take to strengthen this effort and reposition itself for a greater leadership role in science and technology of the 21st century.