Prevalence and association of human parvovirus B19V with hepatitis B and C viruses in Nigeria

Co-infection of parvovirus B19 with hepatitis B virus has been found in patients with acute and chronic hepatitis. The clinical significance of parvovirus B19 in hepatitis B co-infected patients is still controversial. In this study parvovirus B19 antibodies and DNA were investigated in serum samples from 76 patients with HBV infection, 17 with HBV/HCV co-infection and 44 healthy controls. In the sera from patients with HBV infection, anti-B19V IgM and IgG antibodies were detected in 24/76 (32%) and 25/76 (33%), in 6/17 (35%) and 8/17 (47%) of HBV/HCV co-infected patients, and in 14/44 (32%) and 12/44 (12%) of a non-hepatitis healthy controls, respectively. B19V DNA was detected in 8/76 (11%) of patients with HBV infection and in 3/17 (18%) of patients with a HBV/HCV co-infection, and in 4/44 (9%) healthy controls. The occurrence of parvovirus B19 DNA was significantly higher in patients with symptomatic HBV 4/20 (20%) compared to asymptomatic HBV carrier 4/56 (7%) (P<0.05). Ten of the positive B19V DNA sequences belonged to B19V genotype 1 while two belonged to genotype 3. The results of this study showed a significant difference in the prevalence of parvovirus B19 DNA in symptomatic HBsAg positive as compared to asymptomatic HBsAg positive individuals; however, the conclusion that parvovirus B19 infection increased the frequency of liver disease was not supported. Long-term longitudinal studies are, however, required to determine the synergistic effect of parvovirus B19 infection in HBV or HBV and HCV co-infected persons.

Rabies and antirabies immunization in South Western Nigeria: knowledge, attitude and practice

Factors responsible for the continued endemicity of rabies in Nigeria were determined by carrying out a knowledge, attitude and practice study among residents of Osun State. Structured questionnaires were administered to 679 individuals comprising students, traders and civil servants. Only 33.4% of the respondents knew rabies could be prevented by vaccination, while 38.7% believed that the infection could be treated with herbs. Of the 387 victims of dog bite, 240 (62%) never sought prophylactic postexposure treatment. Of the 10 people who received postexposure treatment, only one received the appropriate treatment consisting of washing, disinfection of wounds, tetanus toxoid and complete antirabies immunization.

Absence of HIV-1 and HIV-2 seroconversions in a cohort medical students in a Nigerian medical school

A cohort of 70, HIV-1 and HIV-2 seronegative medical students were followed up for 30 months, after which 65 were retested for HIV antibody. None of the students was infected by HIV during the period of study. A questionnaire survey carried out showed that all the students had a very good knowledge of HIV, its mode of transmission, control and prevention. Most of the students have never had sex or had a single sex partner and used condoms always or most of the time during sexual intercourse.

Preliminary studies on the use of solid-phase immunosorbent techniques for the rapid detection of Wesselsbron virus (WSLV) IgM by haemagglutination-inhibition

Serum samples from 446 randomly selected persons belonging to different age groups and locations in Nigeria were tested for the presence of WSLV IgM using the flavivirus haemagglutination-inhibition (HI) test adopted to the solid-phase immunosorbent technique (SPIT). 61 (14%) persons had IgM to WSLV only, while 9 (2%) persons had heterologous IgM to WSLV and two other flaviviruses, namely yellow fever and Uganda S viruses. There was a high prevalence of IgM in people of younger age groups than those in older groups. The majority of the IgM positive sera (67 (96%) of the 70 positive sera reacted to high titres (>21:80). With the conventional HI tests, 314 (70%) of the total sera tested had HI antibodies to one or more flaviviruses (yellow fever, West Nile, Potiskum, Zika and Uganda S) out of which 305/314 (97%) had antibodies to 3 or more flaviviruses used in the tests. Although SPIT may not be as sensitive as the conventional HI test, it was found to be more specific and could be adopted for the detection of early WSLV infections in flavivirus hyperendemic environments.

Antigenic relatedness of selected flaviviruses: study with homologous and heterologous immune mouse ascitic fluids

The antigenic relationship of 9 flaviviruses, Yellow fever (YF), Wesselsbron (WSL), Uganda S (UGS), Potiskum (POT), West Nile (WN), Banzi (BAN), Zika (ZK), Dengue type 1 (DEN-1) and Dengue type 2 (DEN-2), was assessed by cross-haemagglutination-inhibition (Cross-HI) and cross-complement fixation (Cross-CF) reactions between each of the viruses and their homologous immune mouse ascitic fluids. Titre ratios were calculated using the heterologous and homologous titres. Cross-CF reactions revealed wider antigenic variations among viruses than Cross-HI reactions. There was no significant antigenic variation between WSL, POT and YF viruses using either of those methods. However, definite differences in antigenicity were observed between them and UGS, BAN and ZK viruses. There were no significant differences between UGS, BAN and ZK or between DEN-1 and DEN-2. The serological relationship among flaviviruses is important in establishing diagnosis and epidemiology of these infections in Africa.

Acute bronchiolitis in tropical Africa: a hospital-based perspective in Ibadan, Nigeria

In a 30-month prospective study of severe acute lower respiratory infections in hospitalized pre-school Nigerian children, acute bronchiolitis was diagnosed in 67 cases; 19 (28.4%) and 2 (3.0%) of these had concomitant pneumonia or croup, respectively. The peak prevalence was in the wet (rainy) season (May-October). The male/female (M:F) ratio in infants < or = 6 months was 2.9:1, differing significantly from the 1.1:1 in older subjects (P = 0.04). None of the subjects had severe malnutrition. Neither a high fever (> or = 39 degrees C), nor tachypnea on admission was significantly correlated with co-existing pneumonia. Of the 29 subjects in whom it was possible to explore viral immunofluorescence studies and/or serodiagnosis, we identified 26 viral identifications in 18 (62.1%) cases; 6 (20.7%) had > or = 2 viruses. Respiratory syncytial virus was identified in 11 (38.0%) of the 29 cases, and parainfluenza virus (PIV) types 1, 2, and 3 in 10 (34.5%). PIV type 3 accounted for 7 cases, including 3 with bacteremia. Bacterial isolates were made in 9 (21.4%) of 42 blood cultures and in the only lung aspirate; Staphylococcus epidermidis and Staphylococcus aureus accounted for 4 and 3 cases, respectively. Although bacteremia was 2.9 times more common in cases with co-existing pneumonia or croup, the respective frequency of virus-positive cases and that of bacteremia was not significantly different between cases with bronchiolitis alone and those with associated pneumonia or croup. No deaths were recorded, but subjects aged > 6 months had a significantly shorter hospital stay than those < 6 months old (P = 0.02). Despite the limited sample size, our findings reflect the etiological importance of the paramyxoviruses and the seasonal pattern of bronchiolitis in tropical Africa.

Wesselsbron virus antibody in domestic animals in Nigeria: retrospective and prospective studies

Retrospective and prospective serological surveys to determine the prevalence of Wesslsbron (WSL) virus infections in animal populations were carried out in different vegetational zones in Nigeria. Sera from 1,492 animals comprising 292 camels, 81 horses, 4 donkeys, 320 cattle, 235 sheep, 260 goats, 114 pigs, 101 dogs and 85 domestic fowls were assayed by haemagglutination-inhibition (HI) test for presence of antibodies to WSL virus and other flavivirus antigens: Yellow Fever (YF), Potiskum (POT), Banzi (BAN), Uganda S (UGS) and West Nile (WN) viruses. Four hundred and eighty one (32%) of the total sera tested were positive for the presence of flavivirus antibodies. The prevalence rates among animals varied with species and vegetational zones of the country. The highest prevalence was noted in animals from a swamp forest zone and was higher among camels, horses, donkeys and sheep when compared with goats, pigs and fowls in different zones. Although monotypic reactions with WSL virus antigen were observed in positive sera, the majority of the WSL virus positive sera cross-reacted with more than two other flavivirus antigens. Serological cross-reactions were most extensive in WSL virus positive horse sera. A ten month sentinel survey among 28 cattle, 68 sheep and 30 goats revealed considerable activity of WSL virus in Nigeria. Of these, 11 cattle and 12 sheep showed antibody conversion to WSL virus antigen. None of the goats seroconverted. Although, there are no records of outbreak of WSL disease in Nigeria, this study revealed that WSL virus is actively circulating among livestock populations in this environment. Flavivirus nucleotide data are needed for final determination of genetic relatedness in this group of viruses.

Respiratory syncytial virus--associated lower respiratory diseases in hospitalised pre-school children in Ibadan

An analysis of the features of lower respiratory diseases (LRD) associated with Respiratory Syncytial Virus (RSV) in 21 children aged 1-23 months, indicated that the clinical features did not differ appreciably from those described for LRD due to other infective agents. It was however, remarkable that none of the children was grossly malnourished, neither was there any death. The final respiratory diagnoses were bronchiolitis alone (6 cases), bronchopneumonia (6 cases), empyema/pleural effusion (3 cases, including one with bronchopneumonia), lobar pneumonia (3 cases, including one with associated bronchopneumonia). Streptococcus pneumonia and Klebsiella pneumoniae respectively, were isolated from blood culture in the two cases with lobar pneumonia alone. One child had laryngotracheobronchitis (croup) alone and another, croup associated with bronchiolitis and bronchopneumonia. Radiologically, the single most common lesion was patchy consolidation (8 cases) followed by hyper-inflation (6 cases); in one case, there was no observable lesion on the chest radiograph. All the 6 children who had bronchiolitis alone were aged 12 months and below, and were well nourished; conversely, 8 of the 12 children with pneumonia alone or in addition to other lesions and both children with pleural effusion, were older than 12 months and underweight. Other viral agents were identified in 8 (38%) of the cases. Complications included heart failure in 4 cases and a combination of anaemia and heart failure in one child with empyema. In a child with symptom complex and radiological features suggestive of acute obstructive lower respiratory infection with immunofluorescence evidence of RSV infection, age and nutritional status are important factors in determining the need for antibiotic therapy pending the outcome of bacterial cultures.

Dengue type 1 epidemic with haemorrhagic manifestations in Fiji, 1989-90

A dengue type 1 epidemic occurred in Fiji between July 1989 and July 1990. Virus isolation in C6/36 cell cultures and Toxorhynchites mosquitos yielded 36 strains. Of the 3686 cases recorded by the Ministry of Health, 60% involved indigenous Fijians and 37%, Indians. A house-to-house survey revealed that a large majority of patients had classical dengue symptoms and 8% reported haemorrhagic manifestations. Among the children and adults hospitalized for dengue, 43% had haemorrhagic manifestations, including epistaxis, gingival bleeding, haematemesis, melaena and haematuria. A total of 15 patients with haemorrhagic manifestations and/or shock died, 10 of whom were aged 0-15 years; the diagnoses were confirmed in four cases by virus isolation or serology.

A survey for haemagglutination-inhibiting antibody to West Nile virus in human and animal sera in Nigeria

A survey for West Nile Virus (WNV) haemagglutination-inhibition (HI) antibody was carried out in humans and domestic animals. Human sera were collected from Ibadan, while the animal sera were collected from both Ibadan and Maiduguri. Out of 304 human sera tested, 123 were positive (40%). There was a higher prevalence of HI antibody in adults than children. Sex distribution of positive sera showed that 37% of males and 43% of females had WNV HI antibody. There was no significant difference in the prevalence of HI antibody in both sexes. On the 123 WNV HI positive sera tested, 104 (85%) and 78 (75%) had yellow fever and Potiskum HI antibody respectively. Monotypic WNV virus reactions were frequently found in children while polytypic reactions were frequently found in adults. A total of 200 animal sera were examined, 50 camels, 50 goats, 49 cattle and 51 sheep. The highest prevalence of HI antibody was found in camels (26%), followed by sheep (20%). Percentage of positive sera in other species were: goat (18%) and cattle (6%). Of the 35 WNV HI positive animal sera, 26 and 20% reacted with Yellow fever and Potiskum virus antigens respectively.

Yellow fever haemagglutination-inhibiting, neutralising and IgM antibodies in vaccinated and unvaccinated residents of Ibadan, Nigeria

A survey for yellow fever virus haemagglutination inhibiting (HI) and neutralising (N) and IgM antibodies was carried out in unvaccinated people in Ibadan and in those immunised with the yellow fever 17-D vaccine. A total of 207 people were tested for HI antibody to yellow fever and two other flaviviruses namely: Wesselsbron and Uganda S. viruses. Prevalence of HI antibody to each flavivirus antigen was as follows: Yellow fever 26%, Wesselsbron 18% and Uganda S 33%. Of the 207 people, 37 (18%) had yellow fever N antibody. There was a higher prevalence of N antibody to yellow fever virus in adults than children. Twenty-one people vaccinated with 17-D yellow fever vaccine donated post-vaccination sera; 10 (48%) had no prevaccination HI antibody, 7 (33%) had HI antibody to one flavivirus and 4 (19%) to two or more flaviviruses. Ninety percent of seronegative people and all those with prevaccination flavivirus antibodies developed HI or N antibody, following vaccination. A total of 58 unvaccinated people were tested for yellow fever IgM antibody by an enzyme linked immunosorbent assay, 2 (3%) were positive; suggesting that active yellow fever transmission was in progress at the time of survey.

Serological evidence for influenza virus activity in Nigeria (1985-1987)

A study to determine the activity of influenza virus among the children population was undertaken between 1985 and 1987 in Nigeria. Paired sera were obtained from children presenting with respiratory diseases at the children emergency and outpatient clinics of the University College Hospital, Ibadan. Forty-two paired sera were examined by haemagglutination-inhibition test to determine HI antibody level of the patients to different serotypes of influenza virus. Ninety percent of the children showed serological evidence of previous contact with influenza A virus subtypes while only 24% were positive when tested against influenza B virus. Twenty-two of the 42 children tested seroconverted to influenza A virus strains while only 2 seroconverted to influenza B virus strain used. Out of the 22 children that seroconverted to influenza A virus, 14 were due to H3N2 A/Mississippi 1/85, 4 to H3N2 A/Leningrad 360/86 and 2 each seroconverted to H1N1 A/Chile 1/83 and H1N1 A/Taiwan 1/180. Two other individuals showed serological conversion to either H3N2 A/Mississippi 1/85 and H1N1 A/Chile 1/83 or H3N2 A/Mississippi 1/85 and H1N1 A/Taiwan 1/86. While cases were seen throughout the year during the period under review, more cases occurred during early (April-May) to peak raining season (September) and during harmattan period (November) in Ibadan area where the study was conducted. It is evident from this study that continuous and synchronous circulation of influenza viruses occur in this environment. There is therefore danger of influenza epidemic under depressed immunity and if the virus is introduced into population with low level of immunity in other parts of the country.

Wesselsbron virus infection in West African dwarf goats (Fouta djallon): virological and immunological studies

West African dwarf goats were experimentally infected with Nigerian strain of Wesselsbron virus. Viraemia was detected in infected goats 2 days after infection and lasted for one day. A 100% mortality was observed among the infected animals; the virus was reisolated in mice from almost every tissue obtained from the bodies of infected goats. In addition, the infected goats developed complement-fixing and haemagglutination inhibiting antibodies to Wesselsbron virus.

An epidemiological study of rotavirus diarrhoea in a cohort of Nigerian infants: I. Methodology and experiences in the recruitment and follow-up of patients

A community-based prospective study was carried out in the city of Ibadan, Nigeria, to determine the epidemiology of rotavirus infection and diarrhoea among children in the first two years of life. Implementation of the proposed study methods was hindered by a number of factors common to large urban areas in developing Africa. These factors included difficulties in recruiting the study sample because of maternal fears, cultural beliefs, and lack of paternal consent. Following recruitment, longitudinal surveillance was made difficult by inefficient telecommunications, a haphazard house numbering system, transportation difficulties, mobility of the population, and lack of incentive for continued participation. Despite these difficulties, 73% of the recruited newborns remained in the study until they reached the age of 12 months. The drop-out rate in the second year of study was higher, largely because fewer incentives could be provided during the second year. This paper reviews the operational considerations of implementing a longitudinal study protocol under these conditions, and discusses the potential impact of these problems and the measures taken to overcome them on the results of this study.

An epidemiological study of rotavirus diarrhoea in a cohort of Nigerian infants: II. Incidence of diarrhoea in the first two years of life

In a community-based prospective study of diarrhoeal diseases carried out in Ibadan, 131 infants were selected at birth. The maximum possible length of follow-up ranged from 16 to 24 months. Weekly surveillance for diarrhoea was carried out at home by Primary Health Care workers. Each child was also required to attend a monthly clinic. Of the 131 babies, 95 (73%) completed at least one year of follow-up. All of these had at least one episode of diarrhoea within the first year of life. The incidence rate of diarrhoea in the first year of life was 3.2 cases/child/year. The mean duration of diarrhoea days in the first year of life was 16 per child per year (range 3-34 days). The peak incidence of diarrhoea and the greatest number of diarrhoea days were in the age interval 6-9 months. The mean duration of diarrhoea was five days per episode. Faecal samples for 280 diarrhoea episodes during the first year of life were examined for rotavirus using the ELISA technique: 22 (7.7%) were found to be positive. The mean duration of rotavirus diarrhoea episodes was eight days.

Igbo-Ora virus (an alphavirus isolated in Nigeria): a serological survey for haemagglutination inhibiting antibody in humans and domestic animals

Sera from humans and animals were tested for antibodies to Igbo-Ora virus by the haemagglutination-inhibition test. Prevalence in the human population (3.6%) was lower than that in the animal population (24.5%) in the same locality. No antibodies were detected in persons less than 20 years of age; the highest prevalence of antibodies was found in those above 40 years old. Among the animal species examined, cattle showed the highest prevalence (40%) of antibodies to Igbo-Ora virus. The potential hazard of the virus to human health is discussed.

1987 yellow fever epidemics in Oyo State, Nigeria: a survey for yellow fever virus haemagglutination inhibiting antibody in residents of two communities before and after the epidemics

A survey for yellow fever haemagglutination inhibiting antibody was carried out before and after the 1987 yellow fever epidemics in Nigeria in two localities in Oyo State, namely: Ibadan and Ogbomosho. A total of 129 sera were collected from the two localities before the epidemic. The overall prevalence of yellow fever HI antibody was 37%. A breakdown of positive sera showed that 30/100 and 18/29 sera tested in Ibadan and Ogbomosho respectively were positive. There was a higher prevalence of HI antibody in males (43%) than in females (32%). Of the 48 yellow fever positive sera 23(47%) contained HI antibody to West Nile and 26(52%) to Potiskum viruses. Following the epidemic and the subsequent mass vaccination campaign with the 17D yellow fever vaccine, 200 sera were randomly collected from the same localities. The overall prevalence of yellow fever HI antibody was 67%. The percentage of positive sera in the individual locality was 63% in Ibadan and 73% in Ogbomosho. No statistical difference was observed in the prevalence of yellow fever antibody in both sexes following the yellow fever vaccination campaign (P greater than 0.05). Tests on yellow fever HI antibody positive sera collected after the vaccination campaign showed that 74% and 82% were positive for West Nile and Potiskum HI antibody respectively. Results of this study showed that despite the massive antiyellow fever vaccination campaign there was still a high percentage of seronegative persons in the two communities.

Potiskum virus: enhancement of replication in a macrophage-like cell line

Replication of Potiskum virus was studied in P388D1 macrophage-like cell line in the presence and absence of subneutralizing concentrations of specific antiviral antibody. The cultures were infected at multiplicities of infection (MOI) ranging from 0.4 to 0.0004. The virus replicated to high titres at all MOI tested, but there was an enhancement of virus replication in cultures supplemented with the antibody. Enhancement of replication was MOI dependent, the highest ratios being obtained in cultures infected at lowest MOI. In enhancement assays using various dilutions of immune mouse ascitic fluid (IMAF), the highest enhancement ratio was observed at dilution 1 : 500; the enhancing antibody titre was 5,000.

Neonatal rotavirus infection in urban and rural communities in Nigeria

Two hundred and thirteen neonates from an urban and a rural community in Nigeria were examined for neonatal rotavirus infection. Twenty-four (11%) were shedding rotavirus in their stools. All newborns shedding rotavirus were either asymptomatic or had very mild diarrhoea. Most infections (71%) were detected during the first week of life; 21% and 8% occurred in the second and third weeks respectively. ELISA subgrouping of the rotavirus strains obtained from these neonates showed that 30% belonged to subgroup I and 70% to subgroup II. A survey for rotavirus antibody in a revealed that 67% of these children had antibody in their cord sera. Most of the newborns shedding rotavirus in stool had passively acquired antibody in their sera.

Antibody-mediated enhancement of Wesselsbron virus in P388D1 cells

Antibody-mediated enhancement of Wesselsbron virus was investigated in P388D1 cell cultures. Virus infection was enhanced in culture by various dilutions of homologous and heterologous flavivirus antibody. Highest enhancement ratios and enhancing antibody titres were obtained with the homologous antibody. Enhancement of Wesselsbron virus infection in P388D1 cultures was also dependent on the multiplicity of infection (MOI) used; cultures infected at the lowest MOI produced the highest enhancement ratios. Of the four heterologous flavivirus IMAF tested for ability to enhance Wesselsbron virus infection, Potiskum virus antibody produced highest fold enhancement and possessed the highest enhancing antibody titre. Zika, Uganda S and Dakar bat IMAF produced lower fold enhancement and had lower enhancing antibody titres.

Rotavirus infection in children presenting with acute gastroenteritis Ibadan, Nigeria

Faecal samples from 84 children presenting with acute gastroenteritis at the University College Hospital, Ibadan, Nigeria and 28 from a non-diarrhoeal control group were tested for rotavirus by an ELISA. 18 cases (21%) and none of the controls were positive. Hospital in-patients had a higher percentage of positives (25%) than did out-patients (10%). The age distribution of infections showed that the highest infection rate (67%) occurred in children four to six months old. Percentages of positive samples from other age groups was as follows: 0 to 3 months, 13%; 7 to 12 months, 33%; and 13 to 24 months, 16%. None of the faecal extracts from children older than two years was positive for rotavirus.

Arthropod-borne virus antibodies in sera of residents of Kainji Lake Basin, Nigeria 1980

A survey for haemagglutination-inhibiting arthropod-borne virus antibody was carried out in the Kainji Lake area of Nigeria. Of 267 persons tested, 139 (52%) and 158 (59%) had alphavirus and flavivirus group HI antibody, respectively. The prevalence of antibody to individual virus antigen is as follows: Chikungunya, 45%; Semliki Forest, 25%; Sindbis, 33%, Yellow fever, 31%, Dengue type 2, 46%; and Zika 56%. The presence of high antibody rates to Chikungunya, Dengue type 2 and Yellow fever viruses is of public health significance. These viruses have been identified as the most important arthropod-borne viruses causing human infections in Nigeria.

Zika virus infections in Nigeria: virological and seroepidemiological investigations in Oyo State

A study of Zika virus infections was carried out in four communities in Oyo State, Nigeria. Virus isolation studies between 1971 and 1975 yielded two virus isolations from human cases of mild febrile illness. Haemagglutination-inhibition tests revealed a high prevalence of antibodies to Zika and three other flaviviruses used. The percentages of positive sera were as follows: Zika (31%), Yellow fever (50%), West Nile (46%), and Wesselsbron (59%). Neutralization tests showed that 40% of Nigerians had Zika virus neutralizing antibody. Fifty per cent of zika virus immune persons had neutralizing antibody to Zika alone or to Zika and one other flavivirus. A total of 121 sera had antibody to Zika virus; of these 48 (40%) also showed antibody to two other flaviviruses, and 12 (10%) had antibodies to three or more other viruses. The percentage of neutralizing antibodies to other flaviviruses in Zika virus immune sera was 81% to Dengue type 1, 58% to Yellow fever, 7% to Wesselsbron, 6% to West Nile and 3% to Uganda S.

Jos virus infection in domestic animals and primates. Pathogenicity and immunological studies

Three species of domestic animals (rabbits, sheep and goats) and two species of primates Erythrocebus patas monkeys and baboon (Papio anubis) were infected with Jos virus. None of the infected animals developed viraemia or overt clinical disease. Complement-fixing and neutralising antibodies were demonstrated in sera of infected animals.

Studies on transmission of Tataguine virus by Culex (pipens) fatigans mosquitoes

Culex (pipens) fatigans mosquitoes were infected with Tataguine virus by pledget method. Virus was recovered from 40% of mosquitoes that fed on the infective blood meal after 21 days of incubation. Low titres of infective virus were found in the mosquitoes. Tataguine virus was not successfully transmitted to suckling hamsters exposed to the bites of infected mosquitoes.

Biophysical and biological studies on Jos virus (a new tick-borne virus isolated from Nigeria)

Jos virus possessed no haemagglutinating property within pH range 6.0--6.6 at room temperature and 37 degrees C. Haemagglutination-inhibition tests with Jos virus immune mouse ascitic fluid against other arbovirus antigens further confirmed the lack of serological relationships with any of the major arbovirus groups. Serum neutralisation tests showed that nonspecific neuralising inhibitors of Jos virus were absent in normal sera. Jos virus is highly thermolabile; a sharp reduction of virus infectivity occurred on exposure to various temperatures. Ultraviolet irradiation rapidly inactivated the virus; considerable loss of infectivity occurred within one minute of exposure to ultraviolet light. Electron microscopic studies of infected suckling mouse liver revealed necrosis of hepatocytes, phagocytosis of necrotic debris and mononuclear infiltration. Jos virus produced plaques in Vero and duck embryo cell cultures. Assay of stock virus in these cell cultures and in suckling mice showed that mouse inoculation was more sensitive than plaque assay.

Dengue virus infections in Nigeria: a survey for antibodies in monkeys and humans

A retrospective serological survey for dengue immunity was conducted in Nigeria to determine the prevalence of infection in man and non-human primates. Preliminary haemagglutination-inhibition (HI) tests revealed that 63% of persons tested had HI antibodies against one or more of the following flaviviruses: dengue type 1, yellow fever, West Nile and Wesselsbron. Parallel HI and neutralization (N) tests on 179 human sera showed that six of 20 sera (30%) negative for flavivirus HI antibody contained dengue N antibody. This finding emphasized the advantage of the N test over HI in screening for dengue virus immunity. Neutralization tests performed on 1,816 human sera from different geographical locations in Nigeria showed that 45% of Nigerians were immune to dengue type 2 virus. The percentage of immunity in adults aged 20 years and older (51%) was significantly higher than in children (37%) (P less than 0-01). In all four ecological zones sampled, the highest percentage of dengue N antibody was observed in the derived Savannah zone (63%) followed by the rain forest zone (42%). The Southern Guinea savannah and plateau zones had lower percentages of dengue-immune persons. There was a higher prevalence of antibodies in urban (48%) than in rural communities (37%). Tests on dengue-immune sera showed that 35% of such sera contained N antibodies to dengue only or to dengue and one other virus. Therefore, dengue immunity cannot be explained by heterologous cross reactions within the flavivirus group. In addition, evidence of dengue infection was found in monkeys and galagos. 48% of monkeys and 25% of galagos contained dengue N antibody. The presence of specific dengue N antibodies in a few sera suggests that the occurrence of a forest cycle of dengue is possible in Nigeria.

Yellow fever outbreak in South Eastern State of Nigeria--virological and serological studies

An outbreak of Yellow Fever in South Eastern State involving Uyo, Itu and Abak divisions is presented. The occurrence of few jaundiced cases with fever in places 29-35 km outside Uyo indicated that the epidemic was more widely spread than it was thought. The rural communities appeared to be more severely affected where a considerably large number of unrecorded deaths were reported. Mortality rate was about 56% among hospitalised patients. The diagnosis of Yellow Fever was confirmed by virus isolation and serology This was the first recorded outbreak in this area.

Experimental Rift Valley fever in West African Dwarf sheep

West African Dwarf sheep were challenged with a low mouse brain-passaged Rift Valley fever virus (Ib-AR 55172) isolated from Nigeria. Viraemia, mild febrile reaction and neutralising antibodies were demonstrated in inoculated animals.

Arbovirus studies in two towns in western state of Nigeria

Three hundred and fifty-one persons were tested for HI antibody to arbovirus Groups A, B and Ingwavuma viruses in Ilesha and Oshogbo, two towns in western Nigeria. Chikungunya accouted for most Group A infections (39%). Antibodies to Group B virus were distributed as follows: Dengue 22%, Yellow Fever 25%, West Nile 28% and Wesselsbron 30%. Few sera 5% were positive to Ingwavuma. No virus was isolated from 188 blood specimens processed for virus isolation.