A seasonal SIR metapopulation model with an Allee effect with application to controlling plague in prairie dog colonies.

For wildlife species living among patchy habitats, disease and the Allee effect (reduced per capita birth rates at low population densities) may together drive a patch's population to extinction, particularly if births are seasonal. Yet local extinction may not be indicative of global extinction, and a patch may become recolonized by migrating individuals. We introduce deterministic and stochastic susceptible, infectious, and immune epidemic models with vector species to study disease in a metapopulation with an Allee effect and seasonal birth and dispersal. We obtain conditions for the existence of a strong Allee effect and existence and stability of a disease-free positive periodic solution. These general models have application to many wildlife diseases. As a case study, we apply them to evaluate dynamics of the sylvatic plague in prairie dog colonies interconnected through dispersal. We further evaluate the effects of control of the vector population and control by immunization on plague eradication.

Compliance following referral in the early detection of oral cancer and precancer in Sri Lanka.

An innovative approach for the early detection of oral cancer and precancer within the context of the primary health care system has been field tested in Sri Lanka. The overall compliance in accepting this particular PHC approach for cancer screening, as estimated by arrival at a referral centre manned by consultant staff, was 54.1%. Nearly 80% of those who turned up without needing an additional reminder, did so within the first 2 weeks of case finding. There was a variation in the degree of compliance depending on the primary health care worker who did the screening and referral. Compliance was greater when the screening area was nearer to the referral centre and in subjects who were diagnosed as having a more advanced stage of the disease. Certain practical considerations that contributed to noncompliance were identified. Postal reminders were seen to increase overall compliance by 10.9%.

An in vitro method for estimating biologically available vitamin B6 in processed foods.

1. An in vitro method which used enzymic digestion of the food matrix to release biologically available vitamin B6 is described. 2. Vitamin B6-fortified liquid model foods were thermally processed. After these foods had been freeze-dried, one part was subjected to enzymic hydrolysis at pH 2.0 with pepsin (EC 3.4.23.1) followed by a hydrolysis at pH 8.0 with pancreatin. The vitamins that were found in the supernatant fraction, after an acidified methanol treatment of the hydrolysate, were estimated by high-performance liquid chromatography (HPLC). The other part was given to rats who were kept on a vitamin B6-depleted diet. 3. The biologically available vitamin B6 content of the processed model foods, as determined by rat bioassay, showed good correlation with the vitamin B6 determined by HPLC. 4. It has proved possible to use this in vitro, two-stage enzymic digestion system followed by HPLC determination to determine biologically available vitamin B6 in vitamin B6-fortified processed model foods.

Analysis of B-6 vitamers in human milk by reverse-phase liquid chromatography.

A simple, accurate reverse-phase high performance liquid chromatography (RPLC) method was introduced for the analysis of B-6 vitamers in human milk. The assay consisted of a phosphate buffer (pH 2.9) delivered isocratically through 5 micron ODS column packing, followed by post-column bisulfite derivatization to enhance the detection of PLP (and to a minor extent PL). The vitamers were detected using a fluorescence spectromonitor. Sample run time was less than 30 min. The sensitivity of the method was such that PL, PN, and PLP were detectable to 30 pmol/ml milk and PM and PMP to 5 pmol/ml milk. Total vitamin B-6 content in milk analyzed by RPLC correlated well with the microbiological assay. B-6 vitamer distribution in human milk was similar to values obtained from two different ion-exchange HPLC systems. The RPLC procedure is simpler and faster than the HPLC systems and is suggested for future use in analysis of B-6 vitamer concentrations in human milk.

Utilization of primary health care workers for early detection of oral cancer and precancer cases in Sri Lanka.

Oral cancer presents a serious public health problem in south-east Asian countries. In Sri Lanka and India 35-40% of all cancers are reported to be oral cancers, which are curable if detected in the early stages. The idea that, in developing countries, one of the few practical approaches to early detection of these cases could be through the utilization of primary health care workers was tested in a field study carried out in Sri Lanka. In a control area the subjects with oral lesions were identified by medical/dental officers. In the study, 34 primary health care workers were able, alongside their routine duties, to examine the oral cavity of 28 295 subjects during a period of 52 weeks; 1220 subjects were detected with lesions needing re-examination. The performance of these primary health care workers was very satisfactory in terms of the number of cases detected and the accuracy of their diagnoses, which were verified by re-examination at a specially designated referral centre. The clinical diagnoses of the three categories of lesions detected were as follows: stage 1 lesions for observation (homogeneous or ulcerated leukoplakia), stage 2 lesions for investigation (speckled leukoplakia, erythroplakia, or submucous fibrosis), and stage 3 lesions for treatment (cancer). There was 89% correspondence between the stage 1-3 diagnoses by the health workers and the clinical diagnoses made at the referral centre. However, compliance by patients was low because only 50% of the cases detected in the field attended the referral centre. The cost-effectiveness of this approach to cancer control has been demonstrated.