Promotion of oral fluid methods for evaluation and surveillance of the measles immunization programme in Ethiopia

This work aims to demonstrate the use of oral-fluid methods in evaluating the effectiveness of a vaccination programme at the individual (vaccine conversion) and population levels (herd immunity and virus transmission and origin) within a developing country context. The setting for this work was Ethiopia- a country beset with huge economic, social and logistical difficulties in vaccine programme implementation. The study comprises the following: First, the development and evaluation of highly sensitive measles specific IgG/IgM ELISAs using oral-fluid, second, the application of these assays to evaluate routine and campaign measles vaccination programmes, and third genotyping of measles virus strains circulating in the country, again using oral-fluid samples. Paired blood and oral fluid samples were obtained from787 individuals of all ages from rural Ethiopia for evaluation of the measles enhanced IgG antibody capture (GAC) enzyme linked immunosorbent assay (ELISA). Relative to serum, oral fluid assay sensitivity and specificity were: 97.4% and 91.1% for measles IgG. This work is the development and evaluation of a new method that has contributed scientifically to vaccination programme evaluation and refinement. Pre- and post-vaccine antibody determined in 296 children attending for routine measles immunization in Addis Ababa suggested the average vaccination age at which 92.6% (200/216) seroconversion rate attained was about nine and half months. Oral-fluid based testing show 87.3% (185/212) seroconversion rate for IgM antibody compared to the 92.6% serconversion rate for serum. This work included the development and use of an oral-fluid enhanced MACELISA as a useful substitute to serum in evaluating vaccine seroconversion. RT-PCR was performed for oral-fluid and serum samples collected from outbreaks and sporadic measles cases across the country to study the molecular genotype characteristics of the strains. Sequence analysis of outbreaks and sporadic case samples revealed that the viruses of the D4, D8 and B3 genotypes were found in the country. This study also demonstrates the practicality of integrating oral-fluid based genotyping into measles surveillance efforts. Pre-campaign survey work carried out in Assella town by collecting oral-fluid samples from 1928 children aged 9-59 months visiting vaccination stations, and post-campaign survey work undertaken by cluster-based random sampling of 750 oral fluid samples from eligible individuals aged between 9 months to <20 years clearly show (i) a shortfall in measles 'immunity 'in the target age group (9-59 months), and (ii) a significant deficit in 'immunity' in those too old to have received the vaccine. This work demonstrates for the first time the merit of oral-fluid sampling in evaluating a measles vaccine campaign. The main achievements summarized above, give weight towards the practicality of using oral fluid in evaluating and refining immunization programmes in the developing country setting. It waits to be seen if the non-invasive technology will gain wider support in the measles control activities

Improving sensitivity of oral fluid testing in IgG prevalence studies: application of mixture models to a rubella antibody survey

A method for the analysis of age-stratified antibody prevalence surveys is applied to a previously reported survey of antibody to rubella virus using oral fluid samples in which the sensitivity of the assay used was shown to be compromised. The age-specific distribution of the quantitative results of antibody tests using oral fluids is modelled as a mixture of strong positive, weak positive and negative components. This yields maximum likelihood estimates of the prevalence at each age and demonstrates that, when used in conjunction with mixture modelling techniques, the results of antibody prevalence studies using oral fluids accurately reflect those obtained using sera

Sero-epidemiology of rubella in the urban population of Addis Ababa Ethiopia

We conducted a community-based cluster sample survey of rubella sero-epidemiology in Addis Ababa, Ethiopia in 1994. Among 4666 individuals for whom complete data were available, rubella antibody prevalence was 91% (95% confidence interval: 90, 92). On multivariable analysis, seroprevalence was lower among individuals who were resident in Addis Ababa for 1 year or less. Approx. 50% seroprevalence was attained by age 4 years, and the estimated average age at infection was 5·2 years. The highest age-specific force of infection was estimated to occur in 5- to 9-year-olds. The early age at infection corresponded with a low estimated incidence of congenital rubella syndrome (CRS) of 0·3 per 1000 live births, equivalent to nine cases of CRS in 1994. The predicted critical level of immunity for elimination of rubella via vaccination was 85–91%, requiring 89–96% coverage with a vaccine of 95% effectiveness. Unless very high coverage of rubella vaccine could be guaranteed, the introduction of childhood vaccination could increase the incidence of CRS in Addis Ababa

SOME ASPECTS OF MALARIA PREVALENCE, VECTOR INFECTIVITY AND D DT RESIST AN CE STUDIES IN GAMBELIA REGION, SOUTHERN WESTERN ETHIOPIA

ABSTRACT: Prevalence of Plasmodium falciparum and Plasmodium vivax in thehuman population, infectivity and DDT resistance of Anopheles mosquitoes were studied on samples collected during the peak malaria season of 1990 from Gambella, South West Ethiopia. Mosquito vectors collected were assorted into species and their infectivity with malaria parasites was determined by the enzyme-linked immunosorbent assay (ELISA). In the human population out of a total of 821 individuals examined from nine villages, 4.1% (34) were found to be positive for malaria parasites. Of the 34 positive individuals 5.9% (2) were positive for Plasmodium vivax and 94.1 (32) for Plasmodium falciparum. Although relatively high positivity rates for malaria were observed in 1-4 and 5-14 age groups, the difference in the rates of positivity was not statistically significant for the whole population (P = 0.5077). However, a significant difference in parasite prevalence was detected between the nine localities (P &lt; 0.05). Compared to that of 1989, the overall malaria prevalence rate in the human population significantly decreased in 1990 (P &lt; 0.05). Insecticide susceptibility studies revealed the presence of DDT resistant Anopheles gambiae s.l. mosquitos in Itang. Furthermore, a strong evidence would suspect the vectorial status of A. pharoensis was obtained by detecting salivary gland sporozoite antigens of P. vivax in the head region of two mosquitos. Sporozoite rates of 0.76% (P. falciparum) for A. gambiae s.l. and 0.47% (P. vivax) for A. pharoensis were determined. [Ethiop. J. Health Dev. 1994;8(1):1-8

Pre-and post-vaccine measles antibody status in infants using serum and oral-fluid testing: an evaluation of routine immunization in Addis Ababa, Ethiopia

Despite the use of measles vaccine, measles incidence in Ethiopia remains a serious public health concern. Progress towards the control of measles requires a national capacity to measure programme effectiveness. This includes evaluation of vaccine effectiveness in infants attending the routine immunization. Objective: To evaluate the effectiveness of the measles routine immunization activities in Addis Ababa. Methods: This study evaluated pre- and post-vaccine antibodies in children attending for routine measles immunization in Addis Ababa. Infants who presented to 3 health centres between September-November, 1998 for routine measles vaccination were enrolled in the study. In total 296 infants (median age 9 months) provided blood and oral-fluid samples, of which 230 (77%) returned to provide post vaccine samples (median interval of 15 days). Screening of sera was undertaken using commercial indirect ELISA kits, and of oral fluids using an in-house IgM-capture ELISA. Results: Pre-vaccination serology showed 1.4% IgM positive, 2.0% IgG positive, and 97.0% seronegative. Post-vaccination seroprevalence of IgM and IgG was 91.3% and 85.0%, respectively, and 92.9% overall. The seroconversion rate was 92.6% (95%CI 88.2-95.7). Based on oral fluid results, 87.3% (95% CI 82.0-91.4) of children showed specific IgM antibody conversion. Conclusion: These results are in support of the recommended age for measles vaccination in Addis Ababa, and show the merit of oral-fluid IgM screening as a non-invasive alternative to blood for assessing vaccine effectiveness. Ethiop.J.Health Dev. 2003; 17(3): 149-15

Evaluation of a measles vaccine campaign in Ethiopia using oral-fluid antibody surveys

We undertook a study to demonstrate the potential contribution of oral-fluid (OF) antibody prevalence surveys in evaluating measles vaccine campaigns. In Asela town, southern Ethiopia, oral fluids were collected from 1928 children aged 9 months to 5 years attending for campaign immunization in December 1999 and 6 months later, from 745 individuals aged 9 months to 19 years, in the same location. Measles antibody status was determined by microimmune measles specific IgG enzyme immunoassay (EIA). Antibody prevalence was estimated at 48% in children attending for vaccination (pre-campaign), and 85% post-campaign in the comparable age group. The estimated reduction in the susceptible proportion was 75%. In older children the proportion antibody negative post-campaign was 28% in 7-9 year olds, and 13% in 10-14 year olds levels of susceptibility which raise concern over continued measles transmission. This is the first evaluation of a measles vaccine campaign based on oral-fluid seroprevalence surveys and it demonstrates the merit of oral-fluid surveys in informing health authorities about vaccination strategy refinement. (C) 2008 Elsevier Ltd. All rights reserved

A point-of-care test for measles diagnosis: detection of measles-specific IgM antibodies and viral nucleic acid

OBJECTIVE: To evaluate the performance of a newly developed point-of-care test (POCT) for the detection of measles-specific IgM antibodies in serum and oral fluid specimens and to assess if measles virus nucleic acid could be recovered from used POCT strips. METHODS: The POCT was used to test 170 serum specimens collected through measles surveillance or vaccination programmes in Ethiopia, Malaysia and the Russian Federation: 69 were positive for measles immunoglobulin M (IgM) antibodies, 74 were positive for rubella IgM antibodies and 7 were positive for both. Also tested were 282 oral fluid specimens from the measles, mumps and rubella (MMR) surveillance programme of the United Kingdom of Great Britain and Northern Ireland. The Microimmune measles IgM capture enzyme immunoassay was the gold standard for comparison. A panel of 24 oral fluids was used to investigate if measles virus haemagglutinin (H) and nucleocapsid (N) genes could be amplified by polymerase chain reaction directly from used POCT strips. FINDINGS: With serum POCT showed a sensitivity and specificity of 90.8% (69/76) and 93.6% (88/94), respectively; with oral fluids, sensitivity and specificity were 90.0% (63/70) and 96.2% (200/208), respectively. Both H and N genes were reliably detected in POCT strips and the N genes could be sequenced for genotyping. Measles virus genes could be recovered from POCT strips after storage for 5 weeks at 20-25 ºC. CONCLUSION: The POCT has the sensitivity and specificity required of a field-based test for measles diagnosis. However, its role in global measles control programmes requires further evaluation

Has oral fluid the potential to replace serum for the evaluation of population immunity levels?: a study of measles, rubella and hepatitis B in rural Ethiopia

OBJECTIVE: To assess the suitability of using oral-fluid samples for determining the prevalence of immunity to vaccine-preventable infections. METHODS: Paired blood and oral-fluid samples were obtained from 853 individuals of all ages from a rural Ethiopian community. Oral fluid around the gums was screened for measles- and rubella-specific antibodies using enhanced IgG antibody capture (GAC) enzyme-linked immunosorbent assays (ELISAs), and for anti-HBc antibodies using a prototype GACELISA. IgG antibodies in serum to measles, rubella and HBc were determined using commercial ELISAs. FINDINGS: Relative to serum, oral fluid assay sensitivity and specificity were as follows: 98% and 87% for measles, 79% and 90% for rubella, and 43% and 87% for anti-HBc. These assay characteristics yielded population prevalence estimates from oral fluid with a precision equal to that of serum for measles (all ages) and rubella (ages <20 years). CONCLUSION: Our results suggest that oral fluid could have the potential to replace serum in IgG antibody prevalence surveys. Further progress requires assessment of variation in assay performance between populations as well as the availability of standardized, easy to use assays