Plaque and growth characteristics of different polioviruses isolated from acute flaccid paralysis in Northern Nigeria.

OBJECTIVE: To determine some virulent trait-related properties of poliovirus isolates from children with acute flaccid paralysis following vaccination with oral polio vaccine (OPV). DESIGN: Six polioviruses earlier characterised into wild, vaccine-derived and OPV-like were studied using the plaque morphology and growth kinetics at supra-optimal temperature. SETTING: Department of Virology, University of Ibadan, Nigeria. SUBJECTS: Polio isolates from six children who developed acute flaccid paralysis following vaccinations with various doses of OPV were used. All the children were located in the Northern part of the country where poliovirus is still circulating. MAIN OUTCOME MEASURES: The two vaccine-derived polioviruses acquired wild type characteristics. RESULTS: All the six poliovirus isolates developed different forms of plaques ranging from tiny, small and large. The plaque formed could however not be used to identify the different isolates. Growth of the different isolates at supra-optimal temperature showed that the three wild polioviruses grew to a higher titre when compared with the Sabin 2 control. The two vaccine derived isolates behaved like the wild poliovirus while the OPV-like virus acquired an intermediate characteristics between wild and sabin. CONCLUSION: The wild polioviruses represented in this study are among the last vestiges of the circulating polioviruses found in the world. It is possible that the observed biological properties of wild types 1 and 3 described in the study are typical of the West African polioviruses. These properties will provide useful previews to the final identification of some important clinical isolates especially type 1 which may grow rapidly in cell culture.

Placental transfer and decay of maternally acquired antimeasles antibodies in Nigerian children.

BACKGROUND: In developing countries vaccination against measles virus (MV) is generally administered at 9 months of age, although it is well-documented that protection of most infants by passively acquired maternal MV antibodies is waning before immunization is given. The purpose of this study was to investigate the decay of maternally derived MV antibodies in Nigerian infants as well as to compare a German and Nigerian cohort of paired mothers and newborns regarding the placental transfer efficiency of MV-specific IgG and total IgG antibodies. METHODS: MV-specific IgG antibodies were measured with a commercially available MV-enzyme-linked immunosorbent assay, a recombinant hemagglutinin enzyme-linked immunosorbent assay as well as a neutralization assay. Total IgG values were determined with a standard immunoturbidimetric test. RESULTS: Anti-MV IgG titers were twice as high in German newborns as in Nigerian newborns. An increased concentration of immunoglobulins transferred via the placenta was found only in the German cohort. High concentrations of total maternal IgG reduced the concentration of MV-specific as well as total IgG that crossed the placenta. Furthermore only 17% of the 4-month-old Nigerian infants were still protected against measles. Antibodies had a biologic half-life of 33 days and a biochemical half-life of 48 days. CONCLUSIONS: Our findings demonstrate that the decay of passively acquired MV antibodies occurred even more rapidly than expected resulting in susceptibility to MV in most of the 4-month-old infants in Nigeria. Furthermore transfer of maternal anti-MV IgG and total IgG antibodies to the newborn was more efficient in the German cohort compared with the Nigerian group. These findings suggest the use of alternative vaccination strategies in developing countries to possibly reduce the window of susceptibility against measles.

Protective levels of canine distemper virus antibody in an urban dog population using plaque reduction neutralization test.

Blood samples from 50 dogs were collected at three veterinary clinics in Ibadan and Abuja, Nigeria and the serum from each sample was evaluated serologically for neutralizing antibodies against canine distemper virus (CDV) by the highly sensitive plaque reduction (PRN) neutralization assay. Thirteen dogs had plaque reduction neutralization titres of 0-100, seven had titres of 100-1,000 while 30 had titres ranging from 1,000-6,000. The PRN titres of vaccinated dogs were found to be significantly higher than unvaccinated dogs. The widespread use of the highly reproducible PRN test for the evaluation of antibody response to CDV may be very important in the generation of international CDV positive serum standards that should help to improve pre-and post-vaccination testing of dogs worldwide.

Field trial of combined yellow fever and measles vaccines among children in Nigeria.

The compared tolerance and immunogenecity of yellow fever and measles vaccines administered separately or combined were evaluated in Nigerian children aged between six to eight and nine to twelve months. The vaccines were well tolerated by both age groups of children, however pyrexia which responded to analgesic was the commonest post vaccination reaction in all the groups of the vaccinated children. Immune response to the vaccines either when given separately or combined was excellent in all the vaccinated groups. Antibody titre and seroconversion rate were always higher in the group that received the combined vaccines together. Our results confirmed that combined yellow fever and measles vaccines are safe for children aged between six to twelve months and we therefore recommend that yellow fever be incorporated into the EPI programme and be given together with measles at the age of nine months.

Herd immunity to measles virus in a population of student nurses and medical students following a widespread outbreak of clinical measles in Ibadan, Nigeria.

Following an outbreak of serologically--and virologically--confirmed measles requiring large-scale hospitalisation of children in Ibadan, Nigeria, the herd immunity to measles virus among medical students and student nurses was determined. Of the 200 students tested, none lacked haemagglutination--inhibiting antibody to measles virus. The titre of HI--antibody ranged from 2(5) to 2(10). Describing a titre of 2(9) as very high, a significantly higher proportion of student nurses than medical students (P < 0.05) had very high antibody titres to measles virus. There was however no statistical difference between the sexes (P > 0.05). Using a commercial Enzyme Immuno Assay kit (EIA), anti measles IgM could not be detected from any of the students. Thus a clear evidence of recent infection with measles virus during the outbreak could not be detected among the students, a probable indication that student nurses and medical students may not participate in the maintenance of wild measles virus within the hospital environment in developing countries like Nigeria.

Hepatitis B surface antigen (HbsAg) in the sera of medical, nursing and microbiology students in Ibadan, Nigeria.

A total of 331 serum samples collected from medical students, student nurses, microbiology students, and patients presenting with Pyrexia of Unknown Origin (PUO) were tested for the presence of Hepatitis B surface Antigen (HbsAg). While only seven (14.0%) of 50 microbiology students (mean age 24.0 years) tested positive for HbsAg, six (6.7%) of 89 student nurses (mean age 21.6 years) and 13 (13.5%) of 95 medical students (mean age 24.3 years) in the clinical phase of their study were found to have HbsAg in their sera. Also, 10 (10.3%) of 97 patients with PUO (mean age 25.4 years), a group of patients from whom medical personnel are most likely to often collect blood for laboratory studies, were found to have HbsAg in their sera. No significant difference was found in the prevalence of HbsAg among the different groups examined in this study (P>0.05). The result of the study thus shows that medical and nursing students, unlike what is known for practising nurses, physicians and surgeons are not at a higher risk of HBV transmission than students of botany and microbiology. Likewise, patients with PUO do not constitute a group that is more likely to transmit HBV to medical personnel than other groups of patients. Vaccination against hepatitis B virus during the early period of medical and nursing training may therefore go a long way to reduce the high prevalence of hepatitis B virus infection previously reported among practising health personnel in Nigeria.

Phylogenetic analysis of new hepatitis B virus isolates from Nigeria supports endemicity of genotype E in West Africa.

Isolates of hepatitis B viruses were collected from 20 acute and chronic hepatitis patients in a highly endemic region of Nigeria. Sequencing classified the isolates to the ayw4, as they all contained the amino acid variations characteristic for that serotype. In the pre-S2 region of five isolates, three to seven amino acids were deleted, suggesting that immune escape mutations previously associated only with chronic HBV infection may be observed also in acute disease. Phylogenetic analysis of the complete pre-S2/S (large S) genes (831 nt) demonstrated that all the viruses belonged to the same genotype E. So far, no isolates of genotype E have been found in any other region of the world, including the Americas. This may suggest a relatively recent introduction of this genotype into humans and would explain the relatively low genetic diversity of viruses belonging to this genotype. One genotype E virus had been found previously in a chimpanzee, and viruses belonging to the CHIMP genotype are related to other genotype E viruses. These findings are compatible with a transmission of genotype E viruses from chimpanzees to humans.

An outbreak of African Swine Fever in Nigeria: virus isolation and molecular characterization of the VP72 gene of a first isolate from West Africa.

The isolation of 98/ASF/NG, a strain of African Swine Fever Virus (ASFV) associated with a 1998 epizootic in Nigeria, is reported. This first isolate of the virus from West Africa was identified through a successful polymerase chain reaction (PCR) amplification and sequencing of a 280 base pair (bp) fragment of the Major Capsid Protein (VP72) gene. Further amplification and sequence analysis of a 1.9 kilobase pair (kbp) fragment encompassing the complete VP72 gene showed that the isolate has a 92.2%, 92.4%, and 97.2% homology with previously sequenced Ugandan, Dominican Republican and Spanish isolates respectively. Of the 50 nucleotide changes observed in this highly conserved gene, 45 were found to result in 40 amino acid changes clustered around the central region (position 426 to 516) of the VP 72 protein while changes at the remaining 5 positions were silent. These changes also led to the loss of two out of the seven potential N-glycosylation sites which are in this gene conserved among all isolates. The possible epizootiological implications of such mutations in a highly conserved gene of a DNA virus is discussed in relation to this outbreak.