Immunity to tetanus and diphtheria in rural Africa.

To assess the effect of the Expanded Program on Immunization (EPI) in rural Africa, blood samples were collected in two Kenyan sublocations. Serum antibodies against tetanus toxoid were measured in 155 individuals 1-70 years of age. Titers greater than the protective level of 0.01 IU/ml were found in 47% of the population. Protection was significantly higher in children born after the launching of the EPI (68%) and in women who had been at childbearing age since then (69%). Significantly lower protection was demonstrated in other age and sex-groups. The level of protection in children was equal in the two populations, whereas protection in fertile women was significantly lower in the population living a long distance from a health center. Diphtheria anti-toxin was measured in the samples from one sublocation, and 70 of 84 individuals (83%) had antibody levels greater than the protective level. No age or sex difference could be found, and there was no correlation between response levels to diphtheria and tetanus. This implicates natural infections as an important source of diphtheria antibodies. Our findings demonstrate a need for better coverage of the adult population against tetanus. Furthermore, diphtheria transmission still appears to take place, underscoring the importance of diphtheria vaccination of travelers to rural Africa.

Immunology of cutaneous and visceral Leishmaniasis: a perspective.

Visceral and cutaneous Leishmaniasis have been widely recognised as in vitro models for the differentia! regulation of CD4+ T cell subsets. These subsets are characterised on the basis of partially non-overlapping patterns of cytokine production. Thus, Th l type cells produce IL-2 and IFN y, whereas Th 2 cells produce IL-4 and IL-5. Both cell types are capable of producing other cytokines such as IL-3. The relationship between the functional expression of these populations and disease outcome has become a central focus for vaccine design, with potentially protective antigen formulations being screened for their ability to specifically induce cytokines, characteristic of the host protective reponse. Observations such as these are important in designing therapy and vaccines for most infectious diseases.

Measurement of serum antibodies against native Leishmania gp63 distinguishes between ongoing and previous L. donovani infection.

An enzyme-linked immunosorbent assay (ELISA) using native gp63 for detection of serum antibodies to Leishmania was evaluated. The test identified antibodies in sera from 16 of 16 visceral leishmaniasis (VL) patients and 9 of 12 sera from patients with Trypanosoma brucei infection. In comparison, sera from 80 Danish controls and 40 control donors from a malaria endemic area of Ghana without known exposure to Leishmania were negative, as were sera from 12 Kenyan malaria patients and 9 schistosomiasis patients. After cure of VL, sera rapidly became negative. Only 1 of 7, 1 of 21, and 1 of 27 sera from cured VL patients 6-12 months, 1-2 years and > 2 years after cure were positive. Thus, in contrast to other serological tests for VL, the gp63 ELISA seems to distinguish an ongoing from a past infection. This might prove useful both for diagnostic and epidemiological purposes.

Field application of an ELISA using redefined Leishmania antigens for the detection of visceral leishmaniasis.

Two soluble antigens from Leishmania donovani of 116 kDa and 70 kDa molecular mass, and a soluble mixture of crude antigens, were used in an enzyme-linked immunosorbent assay (ELISA) for the detection of visceral leishmaniasis (VL) in the field, and compared with the direct agglutination test (DAT). The tests were carried out on 8 VL patients, 34 normal individuals from an area endemic for the disease, and 68 former visceral leishmaniasis patients 1-5 years after treatment. The 70 kDa ELISA and the DAT had a sensitivity and specificity of 100% (95% confidence interval 63-100%), while the 116 kDa ELISA and the soluble crude antigen ELISA were 37.5% (9-76%) and 50% (16-84%) sensitive, respectively. When using ELISA (116 kDa or 70 kDa), 68-69% of sera tested 1-2 years, and 92-94% of sera tested 5 years, after treatment were negative. In contrast, when DAT or ELISA with crude antigen were used, the negativity rate was 31% 1-2 years, and 53% 5 years, after treatment. DAT was therefore not an accurate test for diagnosis in the field. The use of the 70 kDa antigen in ELISA was an accurate alternative to DAT in the detection of VL.