Margarita M. Navia

Efficacy of the RTS,S/AS02A vaccine against Plasmodium falciparum infection and disease in young African children: randomised controlled trial

BACKGROUND Development of an effective malaria vaccine could greatly contribute to disease control. RTS,S/AS02A is a pre-erythrocytic vaccine candidate based on Plasmodium falciparum circumsporozoite surface antigen. We aimed to assess vaccine efficacy, immunogenicity, and safety in young African children. METHODS We did a double-blind, phase IIb, randomised controlled trial in Mozambique in 2022 children aged 1-4 years. The study included two cohorts of children living in two separate areas which underwent different follow-up schemes. Participants were randomly allocated three doses of either RTS,S/AS02A candidate malaria vaccine or control vaccines. The primary endpoint, determined in cohort 1 (n=1605), was time to first clinical episode of P falciparum malaria (axillary temperature > or =37.5 degrees C and P falciparum asexual parasitaemia >2500 per microL) over a 6-month surveillance period. Efficacy for prevention of new infections was determined in cohort 2 (n=417). Analysis was per protocol. FINDINGS 115 children in cohort 1 and 50 in cohort 2 did not receive all three doses and were excluded from the per-protocol analysis. Vaccine efficacy for the first clinical episodes was 29.9% (95% CI 11.0-44.8; p=0.004). At the end of the 6-month observation period, prevalence of P falciparum infection was 37% lower in the RTS,S/AS02A group compared with the control group (11.9% vs 18.9%; p=0.0003). Vaccine efficacy for severe malaria was 57.7% (95% CI 16.2-80.6; p=0.019). In cohort 2, vaccine efficacy for extending time to first infection was 45.0% (31.4-55.9; p<0.0001). INTERPRETATION The RTS,S/AS02A vaccine was safe, well tolerated, and immunogenic. Our results show development of an effective vaccine against malaria is feasible.

Duration of protection with RTS,S/AS02A malaria vaccine in prevention of Plasmodium falciparum disease in Mozambican children: single-blind extended follow-up of a randomised controlled trial

BACKGROUND RTS,S/AS02A is a pre-erythrocytic stage malaria vaccine that provides partial protection against infection in malaria-naive adult volunteers and hyperimmune adults. A previous report showed that this vaccine reduced risk of clinical malaria, delayed time to new infection, and reduced episodes of severe malaria over 6 months in African children. An important remaining issue is the durability of protection against clinical disease in these children. METHODS We did a randomised, controlled, phase IIb trial of RTS,S/AS02A given at 0, 1, and 2 months in 2022 Mozambican children aged 1-4 years. We previously determined vaccine efficacy (VE) against clinical malaria in a double-blind phase that included study months 2.5-8.5 (VE(2.5-8.5)). We now report VE in a single-blind phase up to month 21 (VE(8.5-21)). The primary endpoint was time to first or only clinical episode of Plasmodium falciparum malaria (axillary temperature 37.5 degrees C and P falciparum asexual parasitaemia >2500 per microL) detected through a passive case detection system. We also determined VE for other case definitions and for episodes of severe malaria. This study is registered with the ClinicalTrials.gov identifier NCT00197041. FINDINGS During the single-blind phase, VE(8.5-21) was 28.9% (95% CI 8.4-44.8; p=0.008). At month 21, prevalence of P falciparum infection was 29% lower in the RTS,S/AS02A group than in the control (p=0.017). Considering the entire study period, VE(2.5-21) was 35.3% (95% CI 21.6-46.6; p<0.0001) and VE(2.5-21) for severe malaria was 48.6% (95% CI 12.3-71.0; p=0.02). INTERPRETATION These results show that RTS,S/AS02A confers partial protection in African children aged 1-4 years living in rural endemic areas against a range of clinical disease caused by P falciparum for at least 18 months, and confirm the potential of malaria vaccines to become credible control tools for public-health use.

Prevalence and mother‐to‐infant transmission of hepatitis viruses B, C, and E in Southern Tanzania

Hepatitis B and C markers were tested in 980 pregnant women, in the infants born to infected mothers, and in a random sample of 42 and 50, respectively, children born to uninfected mothers in Tanzania. Sixty‐two women (6.3%) were positive for HBsAg and 15 (24%) were HBeAg‐seropositive. Anti‐HCV was detected in 49 women (5%), 15 (31%) of whom had detectable viremia. HCV RNA serum levels were low and only genotype 4 was identified. Sixty‐six women (6.7%) were positive for anti‐HIV, six of whom were coinfected with HBV and one with HCV. Anti‐HEV was negative in the 180 women tested. At 8 months of age, HBsAg was detected in 8% and 2% of children born to HBV‐infected and noninfected mothers, respectively (P = 0.2). Corresponding figures at 18 months of age were 31% and 21% (P = 0.3). When tested at 2 months of age, HCV RNA was not detected in any of the 43 children born to anti‐HCV–positive mothers nor in any of 50 children born to anti‐HCV–negative mothers. At 18 months, only one child, born to an anti‐HCV–positive mother, had detectable HCV RNA. None of the infants born to women with HIV coinfection were infected with hepatitis viruses. This study suggests that exposure to HEV does not occur in southern Tanzania. The prevalence of current HBV infection in pregnant women from rural Tanzania is lower than in other sub‐Saharan areas. In early childhood, HBV infection appears to occur by horizontal rather than maternofilial mechanisms of transmission. The prevalence of HCV infection is similar to that in other African countries. The results of this study show for the first time in Africa that mother‐to‐infant transmission does not play a significant role in the acquisition of HCV infection. J. Med. Virol. 58:215–220, 1999.

Characterization of an Integron Carrying a New Class D β-Lactamase (OXA-37) in Acinetobacter baumannii

Integrons from a clinical strain of Acinetobacter baumannii highly resistant to beta-lactams have been analyzed. The largest (2.2 kb) contained three gene cassettes: an aacA4, an open reading frame of 417 nucleotides, and an OXA-type encoding gene. The oxa gene nucleotide sequence differed from that of the oxa-20 in 2 bp, one of the mutations being silent. The nonsilent mutationgenerated a substitution of glutamic acid for aspartic acid. The new OXA has been named OXA-37.

Haematological and biochemical indices in young African children: in search of reference intervals.

Introduction  The reference intervals of haematological and biochemical indices currently used in Africa are derived from data collected from populations living in industrialized countries. Few studies have been performed in Africa questioning the validity of these values when applied to local African populations.

High prevalence of nalidixic acid resistant, ciprofloxacin susceptible phenotype among clinical isolates of Escherichia coli and other Enterobacteriaceae

Therapeutic failure of infections during their treatment with quinolones has been often described. This may be due to the development of resistance during treatment of an infecting strain which already had diminished susceptibility to quinolones, even though the initial MIC did not exceed the breakpoint. In this study the prevalence of the nalidixic acid resistant, ciprofloxacin susceptible phenotype among Enterobacteriaceae was analyzed. The results showed that 113 out of 151 (74.83%) strains of the Enterobacteriaceae with diminished susceptibility to ciprofloxacin (MICs from 0.06 to 1 microg/ml) were resistant to nalidixic acid (MICs > 32 microg/ml). The Escherichia coli strains presenting this phenotype already have a mutation in the amino acid codon Ser-83 of the gyrA gene, so that the possibility of developing a second mechanism of resistance during treatment is very high.

In vitro activity of rifaximin against enteropathogens producing traveler's diarrhea

Nowadays, around 40 to 60% of Spanish travelers to developing countries develop diarrhea (4). Different enteropathogens have been associated with the development of travelers diarrhea. The levels of prevalence of these enteropathogens as a cause of travelers diarrhea are 42% for diarrheagenic Escherichia coli, 19.4% for Shigella spp., 3% for Salmonella spp., 2% for Campylobacter spp., 2% for Yersinia spp., 2% for Aeromonas spp., and <2% for others (4). Infectious diarrhea is usually a self-limited disease lasting a few days and does not require antibiotic therapy. In some cases, antimicrobial therapy is recommended (2); however, high levels of resistance to several antimicrobial agents have been described. To resolve the problem of this increase in resistance, the activities of new antimicrobial agents should be studied. Rifaximin is a nonabsorbable antibiotic (2, 5, 6) achieving concentrations of 4,000 to 8,000 μg/g in feces, with a common therapeutic dosage being 800 mg divided in two oral administrations (7). The main aim of this study was to evaluate the in vitro activity of rifaximin against enteropathogens isolated as a cause of travelers diarrhea. MICs of several antimicrobial agents for 177 enteropathogens (Table ​(Table1)1) were determined by the agar dilution method according to guidelines of the National Committee for Clinical Laboratory Standards (8). E. coli ATCC 29522 was used as a quality control strain. TABLE 1 MIC50s, MIC90s, and percentages of resistance of each antimicrobial agent for different enteropathogensa MICs at which 50 and 90% of the isolates tested were inhibited (MIC50s and MIC90s, respectively) and the percentages of resistance were calculated for each antimicrobial agent used in this study and are shown in Table ​Table11. The conventional antimicrobial agents, such as ampicillin, cotrimoxazole, tetracycline, and chloramphenicol, showed no or very little activity against the enteropathogens producing travelers diarrhea. A MIC90 of ampicillin of greater than 128 μg/ml was observed against all of the microorganisms, whereas the MIC90s of tetracycline and trimethoprim for all the microorganisms were ≥16 μg/ml. Only nalidixic acid and ciprofloxacin showed MIC90s of 256 and 32 μg/ml, respectively. The MIC90s of chloramphenicol for the different microorganisms were in a range from 8 to >128 μg/ml. Cotrimoxazole and ampicillin have been widely used to treat travelers diarrhea (3, 11, 12), and the long use and sometimes the misuse of these antibiotics have been associated with the increase of resistance levels (1, 10, 12). MIC50s and MIC90s of rifaximin and rifampin were very similar. MICs of rifaximin ranged from 4 to 8 and from 4 to 16 μg/ml, and MICs of rifampin ranged from 4 to 16 and from 8 to 16 μg/ml, for all tested bacteria except Yersinia enterocolitica and C. jejuni. In particular, the MIC50 and MIC90 of rifamixin of 64 and 128 μg/ml, respectively, were observed for Y. enterocolitica and a value of >128 μg/ml for both the MIC50 and MIC90 was achieved for C. jejuni. In this case and only for rifaximin, doses greater than 128 μg/ml were tested to determine the precise MIC50s and MIC90s, which were found to be 256 and 512 μg/ml, respectively. The in vitro activities of rifaximin against strains from stock culture collections of four university-associated teaching hospitals had been previously reported by Hoover et al. (6). In that study, the activities of rifaximin against enteropathogens were found to be as follows: a MIC50 of 4 to 8 μg/ml and a MIC90 of >8 μg/ml. These results are in accordance with ours, even though our strains were isolated from patients who traveled to different geographical areas. In another study, Ripa et al. (9) tested rifaximin against Campylobacter and Yersinia strains collected from patients with diarrhea. The main difference between these studies and ours is the MICs of rifaximin for Y. enterocolitica and C. jejuni, two microorganisms which were isolated from not more than 2% of patients with travelers diarrhea in our laboratory (3). In conclusion, rifaximin is a nonabsorbable antimicrobial agent, reaching high concentrations in the intestinal tract. The concentrations of rifaximin achieved in the intestinal tract are more than 10-fold higher than the MICs of this antimicrobial agent for the different enteropathogens used in our study. In particular, we observed a definitely good in vitro activity of rifaximin against several enteropathogens, such as E. coli, Shigella spp., and Salmonella spp., which is in accordance with clinical and microbiological outcomes of two recent studies of travelers diarrhea (2; H. L. DuPont, Z. D. Jiang, C. D. Ericsson, J. J. Mathewson, J. Aldachi, E. Palazini, L. S. Riopel, D. Ashley, and F. Martinez-Sandoval, Abstr. 39th Intersci. Conf. Antimicrob. Agents Chemother., abstr. 2227, p. 698, 1999).

Mechanisms of fluoroquinolone resistance in Pseudomonas aeruginosa isolates from canine infections.

Chronic otitis externa in dogs is often associated with Pseudomonas aeruginosa infection. Fluoroquinolones are often used for treating such infections. Fluoroquinolone resistance mechanisms were characterized in 10 strains of P. aeruginosa isolated from chronic canine otitis externa. Nine out of ten strains harbored a mutation in the gyrA gene and presented an overexpression of efflux pump(s). There was a good correlation between the lipophilicity of the fluoroquinolone being tested and the effect of the efflux pump inhibitor in the final MIC. Therefore, both mechanisms, mutation in the gyrA gene and increased efflux pump(s), seem to play an important role in the acquisition of fluoroquinolone resistance in veterinary clinical isolates of P. aeruginosa. Levels of resistance to fluoroquinolones suggest that they could not be a good choice for systemic therapy of Pseudomonas otitis.

Relationship between haemoglobin and haematocrit in the definition of anaemia

Introduction  Anaemia is the most frequent haematological disorder in childhood. The notion that defines naemia does not change throughout life, although parameters used for its evaluation show significant variations during childhood. Haematocrit (Hct) (%) is usually defined as three times the value of haemoglobin (Hgb) (g/dl), while the clinical definition of anaemia is related to either an abnormal Hct or Hgb value.

Detection of dihydrofolate reductase genes by PCR and RFLP

The presence of plasmid-encoded trimethoprim resistant dfr genes is the most common mechanism responsible for the acquisition of trimethoprim resistance. The usual method to detect the presence of these genes is hybridization with specific probes. We describe an alternative, faster and easier method, based on PCR amplification and RFLP analysis, to discriminate up to sixteen different dfr genes.