Monitoring of Pertussis
Monitoring of Pertussis Infection in Russia
Tech Area / Field
- MED-DIS/Disease Surveillance/Medicine
- BIO-CGM/Cytology, Genetics and Molecular Biology/Biotechnology
3 Approved without Funding
State Research Center for Applied Microbiology, Russia, Moscow reg., Obolensk
- Gabrichevsky Institute of Epidemiology and Microbiology, Russia, Moscow
- Dalhousie University / Clinical Trials Research Center, Canada, NS, Halifax\nFraunhofer USA - Center for Molecular Biotechnology, USA, DE, Newark\nNational Institute of Public Health and the Environment, The Netherlands, Bilthoven
Project summaryThere is evidence that the incidence of pertussis (whooping cough) has increased in a number of countries, such as Australia, Canada, The Netherlands, the United States and Russia by the end of the 90s of XX century making the control of the disease an urgent problem.
In Russia, systematic vaccination of population against whooping cough having been put in practice for more than 40 years results in considerable changes both in epidemiology and clinical picture of the disease. At the end of the 70s, the reduction of the incidence rate, relief of the severity of clinical presentation and weakening of toxic and virulent properties of the circulating pertussis causative agent strains (replacement of serovar 1.2.3 for 1.0.3) was observed at the background of mass vaccination of the population.
In the 80-90s, new trends in the development of whooping cough epidemic process were revealed. Unlike the events of previous decades, the share of vaccinated baby population began to decrease in connection with progressing growing of the number of children with medical contraindications to vaccination (Farafontova E.G. et al., 1981; Braginskaya V.P. et al., 1985), that had brought to pertussis incidence rise, and the share of the unvaccinated children infected made up to 50-70% (Sigaeva L.A. et al., 1986). In Russia, the incidence of pertussis increased in 2-3 times in the 80s in comparison with the 70s. High incidence rate (IR) was characteristic of the 90s, though in 1992 and 1996 the incidence rate reduction was registered (16,2 and 9,4 per 100 000 population, respectively). High IR was also registered in 1994 (32,9 ) and the years followed, for instance, in 2000. It should be noted that at the background of frequent occurrence of the diseases, IR varied notably from 0 to 50,0. In 1998, the highest IR was registered in Magadansk region (57,9), in the city of Moscow (52,5), St.Petersburg (45,9), Novosibirsk region (45,9), Nizhny Novgorod region (40,6).
Unfavorable epidemic situation has brought about the changes in the severity of whooping cough. Increase of moderate forms from 58,3 % (1977-1981) to 69,2% (in 1989-1995) and reduction of light forms of the diseases from 26,2% to 10,8 % in children at the ages of 0-1 was revealed. In children of older ages, the share of moderate forms of the disease increased from 3,6% to 9,7%. In this period typical forms of whooping cough were registered in 89 % of children older than 1 year. In the 70s, this index made 65,1 %. Such differences in the clinical presentation of whooping cough can be explained by the increase of the share of unvaccinated children. If in 1972-1978 the share of children not vaccinated with DTP vaccine made 7,8%, in 1989-1993, it grew up to 68,3%.
Up to 1995, the level of vaccination remained low, on average from 30,5% (1991) to 60,1% (1995). The level considerably increased in 1996 (80%) and the subsequent years (89% in 1999). However, no significant reduction of the pertussis incidence had occurred.
Beginning from 1996, pertussis incidence in children at the age of 6 and older was observed. Obviously, this fact is likely to be due to the high share of unvaccinated children.
Monitoring of Bordetella pertussis strains circulating in Russia revealed the increase of the number of strains with antigenic factors 1.2.3 and 1.2.0 characteristic of the strains circulating within the pre-immunization period. In 1992, the share of strains of serovars 1.2.0. and 1.2.3 increased in Moscow from 2,3% to 16%. In 1993-1994, the share of serovar 1.2.0 reached 24,8 % and that of serovar 1.2.3 9,8%. The share of moderately toxic strains also considerably increased from 18,5% - 33,4% (at the beginning of the 80s) to 66,6% (in 1990). Highly toxic strains appeared. Thus, there is a dependence between antigenic structure of different serovars, toxicity of B.pertussis strains and severity of the disease (Sigaeva L.A.,1993; Petrova M.S. eta l., 1996).
In the last years, the attention of many researchers has been focused on the studies of B.pertussis antigenic polymorphoism on the models of pertactin (prn) and S1 subunit of pertussis toxin (Ptx S1). In was shown that under natural conditions, in children vaccinated with whole-cell vaccine, selection of antigenically modified variants differing from vaccine strains of B.pertussis in antigenic specificity occurred. Non-vaccine types of pertactin (prn 2) and pertussis toxin (Ptx S1A) replace gradually the circulating vaccine types of prn1 and Ptx S1B (Cassiday P. et al., 2000; Popovic T. et al., 1999). The data of molecular and immunological studies give evidence to the fact that pergency in the antigenic structure of pertactin and pertussis toxin is caused by vaccination with whole-cell vaccine, it is due to the immune selection and is directed on the replacement of earlier existing epitopes for new domains by modification of nucleotide and, therefore, amino acid sequences in the structure of new “non-vaccine” B.pertussis strains. Despite the wide coverage, efficiency of vaccination with “old” vaccine strains appeared to be insufficient (Mooi F.R. et al., 1998, 1999, 2001; Mastrantonio P. et al., 1999; CassidAy P. et al., 2000).
Activation of the epidemic process observed during the last years causes the modification of pertussis clinical picture. There are some difficulties in the diagnosis of the disease, that bring about incomplete registration of the infected persons and, thus, IR underrating. Resemblance of the clinical pictures of whooping cough and parapertussis makes difficult the differential diagnosis of the diseases.
In spite of the development of new diagnostic methods, PCR and ELISA, the problem of laboratory diagnostics of whooping cough is far to be resolved. The previous studies showed that for reliable laboratory diagnostics of whooping cough, a combination of several tests is required. Combination of the causative agent identification and serological reactions is considered to be the most efficient.
Thus, all the aforesaid points to the need of monitoring of B.pertussis strains circulating in Russia in different periods of the epidemic process and study of pathogenic and genetic characteristic of the strains as well as their influence on clinical picture of the disease.
Development and improvement of the methods of molecular-biological monitoring of Bordetella pertussis strains, methods for the diagnostics of the infection and identification of the causative agent on the base of the evaluation of pheno- and genotypical properties of the circulating strains, analysis of the pertussis incidence, severity of the disease and immunity status in order to improve the system of epidemic surveillance of pertussis in Russia is the major objective of the project proposed.
The following results are expected:
- Current situation of pertussis epidemic in Russia will be evaluated;
- Collection of B.pertussis strains will be expanded and characterized;
- Culture-morphological, biochemical and serological characteristics of B.pertussis strains circulating in Russia will be presented;
- Virulent properties of the circulating B.pertussis strains will be studied;
- Nutrient media for cultivation and isolation of B.pertussis strains will be developed;
- Methods for isolation and identification of B.pertussis will be improved;
- Spectra and levels of drug resistance of the isolated B.pertussis strains will be determined;
- Adhesive and cytopathogenic effect of B.pertussis strains on cell cultures will be studied;
- Monoreceptor serum and suspension (latex and erythrocytic) diagnosticums to study the antigens of B.pertussis and anti-pertussis immunity will be prepared;
- Differences between antitoxic immunity in vaccinated children and the diseased persons will be determined;
- Pheno- and genotypical and antigenic characteristics of B.pertussis strains circulating in Russia will be determined;
- Molecular-genetic method for screening of B.pertussis strains with modified genes of pertactin (prn) and pertussis toxin (ptx S1) will be developed;
- Method for evaluation of genetic variability of B.pertussis strain chromosomal DNA will be developed;
- Genotypical variations of the major virulence factors (pertussis toxin, pertactin) and characteristic features of chromosomal DNA of B.pertussis strains circulating in Russia will be revealed;
- Possibility of using molecular-biological characteristics of B.pertussis for forecasting the severity of the disease and intensity of the epidemic process will be evaluated;
- Clinical picture of whooping cough will be studied; criteria of the severity of the disease will be determined;
- Correlation between the severity of the disease, toxigenicity of the causative agent and immunity status will be determined;
- The effect of age-factor, concomitant diseases as well as post-immunization and post-infectious immunity and molecular biological characteristics of B.pertussis caused the disease on the clinical picture and outcome of pertussis will be determined;
- A concept of molecular-biological monitoring of B.pertussis will be constructed; recommendations on the improvement of methods for diagnostics, treatment and prevention of whooping cough will be given.
Specialists, having got a great experience in microbiology of pathogenic infection causative agents, genetic-engineering and molecular-biological investigations will take part in the implementation of the project. Experts engaged in the studies on the monitoring of diphtheria infection will also participate.