Measles vaccine potency and sero-conversion rates among infants receiving measles immunization in Ilorin, Kwara State, Nigeria.

This study was designed to assess the seroconversion rate of measles vaccine among infants receiving measles immunization in Ilorin, Nigeria. The pre- and post-measles vaccination sera of the children were tested using the Haemagglutination Inhibition test. The measles vaccines administered at the immunization centre were also tested for their potency using in-vitro titration method. Only 286 (71.5%) of the vacinees returned to give post-vaccination samples. All the infants screened had low pre-vaccination measles antibody titers. Thirty one (8.0%) of the infants had measles prior to vaccination. The seroconversion pattern showed that 196 (68.6%) of the infants developed protective antibody titers. Low seroconversion rate reported in this study was due to low vaccine potency. The titers of vaccines with low potency ranged between log10(-1.0)-log10(-2.25) TCID/per dose. This was beside other non specific antiviral substances exhibited virus neutralizing activity. Only 3 (50%) of the 6 vaccine vials tested had virus titers of log10(-3.25) to log10(-3.5), which fell above the cut-off point recommended by the World Health Organization for measles vaccines. The sero-conversion rate of 68.6% observed among vaccinees is far lower than the immunity level of 95% required stopping measles transmission in an endemic community. Failure of 31.4% of these infants to sero-convert post vaccination can be attributed partly to administration of sub-potent vaccines. There is need for improvement and maintenance of effective vaccine cold chain system in Nigeria. There is need also for periodic monitoring of post-vaccination antibody titers as well as vaccine potency status in order to ensure development of protective seroconversion rates.

Enteroviruses as a possible cause of hypertension, dilated cardiomyopathy (DCM) and hypertensive heart failure (HHF) in South western Nigeria.

BACKGROUND: Human enteroviruses have long been associated with various diseases of man resulting into a wide range of acute symptoms involving the cardiac and skeletal muscles, central nervous system, pancreas, skin and mucous membranes. OBJECTIVE: To assess the role of enteroviruses in the etiology of hypertension, DCM and HHF. METHODS: We obtained stool specimens from 70 subjects comprising 65 patients and 5 controls and isolation was carried out on RD, L20B, HEp-2C and Vero cell lines and identified by neutralization with standard antisera (RIVM). Thirty-six enteroviruses were isolated and identified to be Coxsackieviruses-B5, A9, Echoviruses 1, 6, 7, 9, 11, 12, 22, 30 and Poliovirus type 1 and 3. RESULTS: Three most frequently occurring enterovirus serotypes which constitute 60.0% of the 30 NPEV typed and 50.0% of all the isolates were Echoviruses, Coxsackie-B5-virus and Coxsackievirus-A9. Echoviruses constituted 50.0% of all the serotypes while Coxsackieviruses-B5 and A9 accounts for the 27.8 % and 5.6% respectively. Enteroviral isolation rate was higher in age groups 51 years and above. The percentage of study subjects who had Coxsackie-B5-viruses and echoviruses was significantly (P<0.05) higher in cases of hypertension, HHF and DCM than in control subjects. Coxackie-B5-virus, Echovirus-6 and Echovirus-11 were found in both study locations. CONCLUSION: The findings of this study showed that Enteroviruses may likely be involved in the etiology of hypertension, DCM and HHF. Further studies would therefore be necessary for the prevention and control of these diseases.

Comparative study of molecular and antigenic characterization for intratypic differentiation (ITD) of poliovirus strains.

This study was designed to compare the sensitivity of a Sabin vaccine strain-specific PCR assay and an enzyme-linked immunosorbent assay with polyclonal cross-absorbed antisera (PAb-E) for intratypic differentiation (ITD) of polioviruses (PVs). These were used for the definitive characterization of the strains. Poliovirus strains isolated in L20B and RD cell lines were subjected to both PCR and ELISA. Both PCR and ELISA identified 3 (13.6%) out of 22 isolates, respectively as poliovirus Sabin 1. PCR identified 4 (18.2%) out of 22 isolates as poliovirus Sabin 2 and ELISA identified 2 (9.1%) out of 22 isolates as poliovirus Sabin 2. None of the two assay identified poliovirus Sabin 3. Both PCR and ELISA identified 12 (54.5%) out of 22 isolates, respectively as wild poliovirus (WPV) 1. None of the assays identified any of the isolates as WPV 2 and 3. Only PCR assay was able to identify the mixture of two poliovirus Sabin serotypes (a mixture of Sabin 1 and 2) and two mixtures of poliovirus Sabin 2 and 3. In this study, only ELISA was able to identified two invalid results. Invalid results observed in this study are of important practical implication to the emergence of vaccine-derived poliovirus. This may have epidemic potential. Hence, the two ITD assays are of paramount importance for identification of PVs. It is therefore recommended in line with WHO guideline that at least two methods be used for the ITD of poliovirus isolates, and each method should be based on a different principle (i.e., antigenic and genetic properties).

Sabin and wild type polioviruses from children who presented with acute flaccid paralysis in Nigeria.

BACKGROUND: Sensitive poliovirus surveillance to detect vaccine-derived-polioviruses will continue to increase in importance. OBJECTIVE: Isolating and identifying poliovirus strains from children of pediatrics age in Nigeria. METHODS: A total of 120 fecal samples were randomly collected from children under the age of five who presented with acute flaccid paralysis. Samples were tested by tissue culture technique and further characterized by intratypic differentiation testing using ELISA and PCR methods. RESULTS: The study confirmed the presence of 22(18.3%) enteroviral isolates comprising 19(86.4%) polioviruses and 3(13.6%) non-polio enteroviruses. These 19 polioviruses include: Sabin-type poliovirus-1 (15.8%), poliovirus-2 (10.5%), poliovirus-3 (10.5%) and wild-type poliovirus-1 (63.2%) isolates. It showed that poliovirus infection was higher in children ages 6-11 months (18.9%), females (18.4%), northern states (91.0%) with no vaccination record (75.0%). Wild-type poliovirus-1 was isolated from the stool samples of 12(54.6%) children from northern states and in all age groups except 18-23 months. No significant differences (P >0.05) between poliovirus infection and age (18.9% vs. 17.7%; 81.9% vs. 18.2%) and sex (18.3% vs. 18.4%). There was significant differences (P<0.05) between poliovirus infection and location (91.0% vs. 9.0%) and history of polio vaccination (75.0% vs. 0.0%). No wild-type poliovirus was found in those with complete vaccination. CONCLUSION: This study further confirms the presence of Sabin and wild-type poliovirus among children in Nigeria. The isolation of Sabin strain of poliovirus is advantageous to the polio eradication program as it is capable of inducing natural immunity in susceptible hosts. Transmission of wild-type poliovirus among children with incomplete vaccination poses a serious threat to polio eradication program in Nigeria. Environmental and serological surveillance with larger sample size are important for monitoring poliovirus circulation in Nigeria.

Non-polio enteroviruses serotypes circulating in Nigeria.

Enteroviruses is one of the most common group of human pathogens, causing a wide range of acute symptoms involving the cardiac and skeletal muscles, central nervous system, pancreas,skin and mucous membranes. In spite of the success recorded in polio eradication globally, infections with other enteroviruses remain frequent and sometimes very serious, requiring hospitalization. In this study we determined the various circulating serotypes of non-polio enteroviruses (NPEVs) with a view to providing information on the activity of these viruses among the Nigerian children, who usually are the most affected. Stool samples were obtained from hospitalized children at two major secondary community hospitals in Ibadan and acute flaccid paralysis (AFP) cases from 26 states ofNigeria. A presumptive identification of NPEVs was based on growth in RD cells. Isolates were identified by neutralization assay using sera obtained from the Institute for Public Health and the Environment, the Netherlands. The problems associated with this assay prompted the use of genotypic method developed at the Centers for Disease Control, Atlanta, USA for the final identification of isolates. Neutralization assay identified the 138 isolates into echoviruses (43.5%), coxsackie B viruses (29.7%) and untypeable isolates (26.8%). Finally genotyping identified echoviruses (E3, E6, E7, E11, E12, E13, E14, E19, E20, E21, E24, E29, E30, E33), coxsackieviruses (CVA3, CVA4, CVA6, CVA17, CVB3, CVB5, CVB6) and enteroviruses (EV69, EV71). The causal association of isolates with different diseases was also established. Majority of the isolates belonged to the human enterovirus gropup B (HEV-B) specie, followed by 4 and 1 in the HEV-A and HEV-C species respectively. This study forms the basis of molecular epidemiology of NPEVs being established for the first time in Nigeria. The implication of the presence of neurotropic serotypes (E3, E6, E7, E11, E14, E20, E24, E29, E30, EV71, CVB3 and CVB5) is that AFP may still be prevalent following polio eradication.

Seroconversion of children following natural measles infection and vaccination.

OBJECTIVE: To evaluate the relationship between measles virus (MV) antibodies (abs) in sera and breast milk of nursing mothers, their contributions in seroconversion of children (0-9 months) post vaccination, prevalence of prevaccination measles abs in sera of children brought for measles vaccination and seroconversion rate in vaccinees from nursing and lactating mothers. Also to determine the potency of vaccines available in Nigeria in relation to seroconversion. METHODS: One hundred and twenty pre- and post-vaccination sera and breast milk samples were collected from each nursing mother while corresponding number of finger prick pre- and post-vaccination sera samples were collected from children on filter papers. These were tested for mv abs using serological techniques. RESULTS: Eighty (20.0%) mothers had measles haemagglutination inhibition (HI) abs in sera and 88 (27.2%) had mv HI abs in breast milk. Eight (2.0%) children who had prevaccination mv abs in sera came from mv ab negative mothers. Forty-four (37.0%) came back for post vaccination sera, sero-converted while 76 (63.3%) gave low sero-conversion rate of 37.0%. Results showed that mv abs in sera or breast milk of mothers did not interfere with mv vaccination in children. The low sero-conversion rate obtained was due to low vaccine potency with titres ranging between (log10-10 - log10-2.5)TCID/per dose, besides non-specific antiviral substances exhibited virus neutralizing activity. CONCLUSION: Poor sero-conversion due to loss of passive immunity arose from undernourishment while low ab titres came with natural infection. This suggested mv vaccination did not immunize following natural mv infection or any other previous immune status.

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.

Passive immunity to measles in the breastmilk and cord blood of some nigerian subjects.

Maternal and cord blood collected from 33 Nigerian mother-child pairs were tested for measles-sepcific IgG. All 33 had protective measles antibodies at the time of delivery with a positive correlation of r = 0.87. Determination of the rate of waning of these antibodies revealed that 58 per cent of these children had lost the protective maternal antibody by the age of 4 months and only 3 per cent of the children had enough antibody to protect them between the ages of 6-9 months. Fifty-five colostrum samples from the same mothers and 347 breastmilk samples collected at various periods of breastfeeding also showed that anti-measles IgA had dropped below the protective cut-off within the first 2 weeks of birth. It is evident that the Nigerian child is born with solid anti-measles antibody but the rate of waning has left a large number unprotected before the first dose of the vaccine. There is an urgent need to review the measles vaccination programme in Nigeria to protect these susceptible infants.

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.

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.

Human immunodeficiency virus antibody in patients with cancer of the uterine cervix undergoing radiotherapy: clinical stages, histological grade and outcome of radiotherapy.

One hundred and twenty consecutive patients with cancer of the uterine cervix were screened for human immunodeficiency virus (HIV) seropositivity before and after radiotherapy. The severity of the disease in terms of clinical staging and histological grading of HIV seropositive women was compared with that of seronegative women. The result showed a prevalence rate of 4.2% for HIV seropositivity which was similar to the rate quoted for the general populace in Nigeria. The HIV seropositive women presented with more severe disease state than the HIV seronegative women. The mean duration of remission was significantly shorter in the HIV seropositive women following radiotherapy (18.36+/3.96 vs. 24.24+/-6.3 months). It was concluded that HIV infection increases the severity and progression of cancer of the cervix in Nigerians. Radiotherapy has no effect on the patients' seropositivity and possibly no effect on the virus. A more aggressive treatment of carcinoma of the cervix and closer follow-up of HIV seropositive patients following treatment are necessary.

Wild polio virus surveillance in the sewage system of selected communities at the risk of poliomyelitis in southwest Nigeria.

Twenty two sewage samples collected from eleven locations among communities at risk of poliomyelitis in the southwestern part of Nigeria were screened for the presence of polio virus. The virus was isolated from seven of the samples. All the isolates were type 1 wild polio virus, an indication that all the isolates were from human contamination and that the wild polio virus is still very much in circulation in Nigeria many years after the Expanded Programme on Immunisation was introduced. It can be concluded from this study that polio immunisation campaign has not been successful in Nigeria considering the number of wild polio virus isolated from the sewage samples since virological examination of sewage has been used to document the effect of vaccination campaigns.

Isolation of Nigerian strains of measles virus.

We have recently succeeded in isolating two measles viruses, Ibn H13153 and Ibn H13154 from the peripheral lymphocytes of two unvaccinated 9 and 12 month old outpatient children at the Institute of Child Health, University College Hospital Ibadan, Nigeria. The viruses have undergone six serial passages in B95a and Vero cell lines where characteristic measles cytopathic effects (CPE) have been noticed. The viruses have been confirmed to be measles by Haemagglutination Inhibition (HI) test and the Indirect Immunofluorescent antibody Test (IFT). Both isolates agglutinated 0.75% monkey rbc. The HA titres were 1:40 and 1:80 respectively. Antigens from the known positive Edmonston strain and uninoculated Vero cell line gave an HA titre of 1:160 and 1:0 respectively. Further characterisation with respect to the polypeptide and DNA components is under way.

Herpetic urethritis in male patients in Ibadan.

In a study of 151 male patients attending a sexually transmitted disease clinic, 40 (26.4%) had non-gonococcal urethritis. Herpes simplex virus was isolated in tissue culture of HEp-2 cell line from 10 of the patients with non-gonococcal urethritis, and identified by complement fixation and indirect immunofluorescent anti body tests. Of the isolates, 30% were Herpes simplex virus type 1 (HSV-1), while 70% were Herpes simplex virus types (HSV-2).

Measles outbreak in Ibadan: clinical, serological and virological identification of affected children in selected hospitals.

An outbreak of measles was investigated in four selected hospitals in Ibadan using clinical, serological and virological methods to identify the affected children. A total of 25 children who were either vaccinated or not vaccinated were involved. Signs and symptoms were, however, more severe among the non-vaccinated children. Measles virus was successfully isolated from three of the children, confirming that the measles virus was involved in the outbreak. Serological tests using both haemagglutination inhibition (HI) and the solid phase immunosorbent test (SPIT) showed evidence of measles antibody in the sera of affected children. The SPIT test was able to detect both IgM and IgA in the sera, indicating that it was a recent infection. Implications of the result obtained in the study for the control of measles in Nigeria is discussed.

PIP: A combination of clinical, serological, and virological methods were used to identify affected hospitalized children during a measles outbreak in Ibadan, Nigeria, in 1996. A total of 25 cases of clinical measles were detected at the 4 hospitals visited, comprising 15% of total pediatric admissions during the study period. 13 of the children had been immunized for measles. In 5 cases, the affected children were 6-8 months of age (younger than the recommended vaccination time in Nigeria). Clinical symptoms included fever, rash, cough, and conjunctivitis. 6 (50%) of the immunized children with measles and 11 (80%) of nonimmunized children had complications such as bronchopneumonia. During the acute phase of illness, the geometric mean antibody titre was 18 among vaccinees and 17 among non-vaccinees. The solid phase immunosorbent test revealed IgM in all sera, indicating recent infection. The finding that more than half of children with measles had been immunized is presumed to reflect the poor quality (i.e., low potency) and short supply of measles vaccine in 1995. An aggressive political effort is required to ensure an adequate measles vaccine supply and quality in Nigeria.

Live viral vaccine potency: an index for assessing the cold chain system.

This study was carried out in the states of Lagos, Oyo, Osun, Nigeria and was designed to assess the efficiency of the cold chain and the potency of the vaccines from the National Cold Store through to the vaccination centres. Storage equipment was inspected and oral polio, measles and yellow fever vaccines were tested for potency. All 27 centres studied had adequately trained staff and storage was shown to be adequate at the National and State Cold Store Level. However, vaccines were adversely affected at the local Government Area Cold Store and Vaccination Centre Levels. Losses of potency of vaccines were shown: loss of titre of oral polio and yellow fever vaccine (0.03-0.9 log) was less than that of the measles vaccines (0.1-2.7 log). This was ascribed to thawing and refreezing due to equipment failure, to intermittent power supply in the absence of standby generators and mishandling of vaccines in the vaccine centres. This study revealed inadequacies at the Local Government Area and Vaccination Centre level. The cold chain should be examined in the remaining states of Nigeria and the inadequacies corrected.

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.

Genital herpes simplex virus infection in females in Ibadan Nigeria.

In a study of female patients attending the Sexually Transmitted Diseases Clinic of the University College Hospital Ibadan, Nigeria, Herpes simplex virus was isolated from the cervix of 5 of 117 patients, a prevalence rate of 4.3%. Two (1.7%) of these patients had HSV in the vagina. The viruses were identified by culture in HEp-2 cell line, chloroform sensitivity test, complement fixation test and indirect immuno-fluorescent antibody technique. Only one (20%) of the five patients has HSV-1 in the endocervix.