Llewellyn J. Legters

Distinguishing high and low anopheline-producing rice fields using remote sensing and GIS technologies

Abstract Worldwide, 140 million ha are devoted to rice cultivation, mostly in developing countries of the tropics and subtropics where malaria still constitutes a serious human health problem. Because rice fields are flood-irrigated on a semi-permanent basis during each growing season, they provide an ideal breeding habitat for a number of potential mosquito vectors of malaria. One of these vectors, Anopheles freeborni , is distributed throughout nearly 240 000 ha of irrigated rice in northern and central California, and may serve as a model for the study of rice field mosquito population dynamics using spectral and spatial information. Analysis of field data revealed that rice fields with rapid early season vegetation canopy development, located near livestock pastures (i.e. bloodmeal sources), had greater mosquito larval populations than fields with more slowly developing vegetation canopies located further from pastures. Remote sensing reflectance measurements of early season rice canopy development and geographic information system (GIS) measurements of distance to livestock pasture were combined to distinguish between high and low mosquito-producing rice fields. These distinctions were made with 90% accuracy nearly 2 months before anopheline larval populations peaked.

Persistence of antibody to hepatitis B surface antigen after low-dose, intradermal hepatitis B immunization and response to a booster dose

To determine the duration of antibody after low-dose, intradermal (i.d.), plasma-derived hepatitis B vaccination and the response to a booster dose, we studied two classes of medical students who were immunized with 2 micrograms doses i.d. In one class, 73/88 (85%) who had been immunized by skilled personnel at 0, 1 and 6 months, had protective concentrations (greater than or equal to 10 mIU ml-1) of anti-HBs at 20 months after the first dose. Twelve (92%) out of 13 students who received only two doses at 0 and 1 months also had protective concentrations at month 20. At month 27, 11/16 (69%) with antibody less than or equal to 10 mIU ml-1 responded to a fourth dose of 2 micrograms i.d. with protective concentrations of anti-HBs. In the second class, after three doses of vaccine at 0, 1, and 6 months, protective concentrations of anti-HBs were present in 90/93 (97%) at 14 months and in 71/80 (89%) at 25 months. In those who received only two doses, protective concentrations were found in 24/31 (74%) at 14 months and 9/16 (56%) at 25 months. After a booster dose of 2 micrograms i.d. at month 25, anti-HBs concentrations rose from a geometric mean of 78 to 1198 mIU ml-1 in 60 subjects previously immunized with three doses and from 18 to 1054 mIU ml-1 in 16 students previously immunized with only two doses. Overall, 73/76 (96%) of students in the second group had protective concentrations of antibody after the booster dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Randomized comparison of 5 and 10 μg doses of two recombinant hepatitis B vaccines

The high cost of hepatitis B vaccines remains an obstacle to their use. Since the recommended adult dose of Recombivax HB (MSD) is 10 μg and that of Engerix B (SKB) is 20 μg, we sought to determine if 10 μg doses of each vaccine are equally immunogenic. Further, since 5 μg doses of Recombivax are routinely used in those ≤ 29 years of age in the US military, we sought to compare this dose with 5 μg doses of Engerix B. Lower doses of Engerix would result in vaccine cost savings. Methods: members of the Belize Defence Force who were ≥ 18 years of age (median 24) without detectable anti-HBc were randomly assigned to receive Recombivax, 5 or 10 μg, or Engerix, 5 or 10 μg IM at 0, 1, and 6 months. Randomization was weighted toward Engerix. Results: after 3 doses, geometric mean concentrations (GMC) of anti-HBs were highest among those receiving Recombivax 10 μg (n=22) or 5 μg (n=46) with GMC anti-HBs of 744 and 570 mIU ml−1, respectively. Similar propertions in the two groups developed ≥ 10 mIU ml−1 anti-HBs (100 and 98%). Among the 91 people who received Engerix 10 μg, the GMC anti-HBs was 325 mIU ml−1 and 91% developed ≥ 10 mIU ml−1. The 87 people who received Engerix 5 μg had the lowest GMC, 177 mIU ml−1 (p 0.05 compared with other regimens). The proportion attaining ≥ 100 mIU ml−1 was lower in the 5 μg Engerix group (63%) compared with 80% in the 5 μg or 95% in the 10 μg Recombivax groups (p<0.05). Conclusions: Engerix administered in 5 μg doses is less immunogenic than 5 or 10 μg doses of Recombivax. In healthy populations < 30 years of age, regimens of half the recommended adult dose (5 μg of Recombivax or 10 μg of Engerix) are highly immunogenic and may result in significant vaccine cost savings.

Yellow Fever Vaccine. IV. Reactogenicity and Antibody Response in Volunteers Inoculated With a Vaccine Free From Contaminating Avian Leukosis Viruses

Summary Removal of avian leukosis viruses (ALV) which have contaminated the yellow fever (YF) 17D vaccine since its development in the middle 1940s, had no effect upon the reactogenicity and antigenicity of this vaccine in man. From results of plaque neutralization (PN) tests, the high degree of antigenicity of the 17D vaccine was confirmed. Preexisting yellow fever antibody appeared to interfere with the antibody response to YF vaccine. Administration of YF vaccine did elicit antibodies capable of cross-reacting with West Nile, and less so with Langat, arbovirus antigens.

Overview of field studies for the application of remote sensing to the study of malaria transmission in Tapachula, Mexico

Abstract A National Aeronautics and Space Administration (NASA) sponsored project to use remote sensing technology in a predictive model of vector population dynamics and malaria transmission potential for the coastal plain of Chiapas, Mexico, is described. Included are the results of recent studies to characterize vector habitats and an assessment of the kinds of information that will be required for developing the predictive model within a geographic information system.

Hepatitis B vaccine booster dose: Low-dose recombinant hepatitis B vaccines as a booster dose

BACKGROUND The timing and best regimen for a booster dose of hepatitis B vaccine have not been determined. METHODS Two studies were conducted to determine the response to a booster dose of 5 micrograms recombinant hepatitis B vaccine. In the first study, a 5 micrograms (0.5 ml) dose of Recombivax HB was administered intramuscularly 38 months after the initial dose to 71 volunteers. In a second study, we offered a 5 micrograms dose recombinant hepatitis B vaccine, either Recombivax HB (0.5 ml) or Engerix B (0.25 ml), to students who had previously been immunized with three doses of vaccine. RESULTS In the first study, among the 44 persons for whom postbooster sera were available, the geometric mean concentration of anti-hepatitis B surface antigens increased from 42 to 2090 mIU/ml after the 5 micrograms (0.5 ml) dose of Recombivax. In the second study, after a 5 micrograms (0.5 ml) dose of Recombivax, the geometric mean concentration increased from 43 to 990 mIU/ml (n = 48), and in the group that received a 5 micrograms (0.25 ml) dose of Engerix B, the concentration increased from 83 to 2337 mIU/ml (n = 45) (p = 0.18 for postdose concentrations). CONCLUSION A 5 micrograms dose of recombinant vaccine results in an excellent booster response at a cost one fourth to one half that of a full 1 ml dose of vaccine.

Initial report of a hepatitis investigation in rural Belize

In spring 1991, Belizian health officials expressed concern about a possible hepatitis outbreak in a banana farming district. A study was designed to identify cases and to address the serological prevalence of hepatitis virus markers. Three populations were studied: (i) persons meeting a clinical case definition for hepatitis; (ii) designated banana workers; and (iii) people in a random sample of households in the community. Information was collected using questionnaires and sera were collected for laboratory testing. This report presents the preliminary results of a study conducted in June 1991. Among people who met the clinical case definition, 24% of 42 tested had immunoglobulin M antibody to hepatitis B virus (HBV) core antigen (anti-HBc IgM). In the worker and household survey populations, 284 and 280 people, respectively, were tested for anti-HBc IgM. In each group, 4% were positive. HBV surface antigen was found in 37% of 43 clinical cases, 18% of workers, and 13% of people in the household survey. Among the 3 study populations, the prevalence of HBV core antibody (anti-HBc) ranged from 73% to 81%. Almost all tested persons had evidence of prior hepatitis A virus infection. Evidence of prior infection with hepatitis viruses A and B was widespread, but an aetiology could not be established for most of the clinical cases. However, the prevalence of hepatitis B markers in this population was very high compared to other reports from the Caribbean.

A remote sensing and geographic information system approach to sampling malaria vector habitats in Chiapas, Mexico

This paper describes a procedure whereby remote sensing and geographic information system (GIS) technologies are used in a sample design to study the habitat of Anopheles albimanus, one of the principle vectors of malaria in Central America. This procedure incorporates Landsat‐derived land cover maps with digital elevation and road network data to identify a random selection of larval habitats accessible for field sampling. At the conclusion of the sampling season, the larval counts will be used to determine habitat productivity, and then integrated with information on human settlement to assess where people are at high risk of malaria. This aproach would be appropriate in areas where land cover information is lacking and problems of access constrain field sampling. The use of a GIS also permits other data (such as insecticide spraying data) to the incorporated in the sample design as they arise. This approach would also be pertinent for other tropical vector‐borne diseases, particularly where human activ...