A.H. Fagbami

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.

Hospital records of human rabies and antirabies prophylaxis in Nigeria 1969–1978

Abstract A survey of human rabies and antirabies prophylaxis was carried out in Nigeria by the use of questionnaires, and review of hospital records and case notes. 169 cases of laboratory or clinically diagnosed human rabies were recorded from 38 hospitals and five state epidemiological units over a 10-year period. 167 (99%) were bitten by dogs, one by a cat and one by a monkey in captivity. Rabies was more frequently encountered in children aged 19 years and under, 70% of cases occurring in this age group. A higher incidence of the disease was also found in the low socio-economic or illiterate group. The lack of awareness of the consequences and seriousness of the disease coupled with the inadequate facilities for post-exposure anti-rabies treatment in rural areas account for the higher rates of rabies in this group. The monthly distribution of the disease shows that more cases of rabies occurred in man during the dry months of the year due to higher incidence of canine rabies during the same period. A total of 7,549 victims of animal bites received post-exposure anti-rabies treatment from 38 hospitals over a 10-year period. The survey also revealed that apart from the normal post-exposure antirabies vaccination, other forms of treatment are sought by dog-bite victims. The dependence on such treatment may contribute to the relatively high incidence of rabies in Nigeria. These studies also show that the antirabies vaccination rate in Nigeria is about 40 to 62 per 100,000 people per annum. The poor state of record keeping, the acute shortage of antirabies vaccine and the failure of some patients to report to hospitals following dog-bites may explain the low rate of post-exposure antirabies vaccination.

Arbovirus studies in Nupeko Forest, a possible natural focus of yellow fever virus in Nigeria I. Description of the area and serological survey of humans and other vertebrate hosts

Abstract Studies were conducted in a restricted area of gallery forest along the middle upper Niger River, Nigeria. Yellow fever neutralizing antibodies were found in 25% of the human population and in 57% of the monkeys tested. Both the abundance of monkeys and the ecological conditions in such forest appear to be favourable for year-round maintenance of yellow fever virus.

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.

Arbovirus studies in nupeko forest, a possible natural focus of yellow fever virus in Nigeria II. Entomological investigations and viruses isolated

Abstract Mosquitoes were collected by several methods during different times of the year in Nupeko Forest; this area is thought to be enzoodemic for yellow fever virus. Potential vectors in the subgenus Stegomyia included Aedes africanus, Ae. luteocephalus, Ae. aegypti , and Ae. simpsoni. Stegomyia populations were very low. Ae. luteocephalus was nevertheless captured on human bait during both the wet and dry seasons, and may be important in maintenance of yellow fever virus transmission. The predominant mosquito in Nupeko Forest was Mansonia africana; this species was captured year-round by various methods including human bait and monkey-baited traps set at various elevations in the forest. No isolates of yellow fever virus were made from the mosquito collections. It is suggested that continuous circulation of yellow fever virus in foci such as Nupeko Forest, which have limited populations of susceptible vertebrate hosts, may depend upon a transmission cycle involving a biologically inefficient vector (e.g. M. africana) or an efficient vector present in small numbers (e.g. Ae. luteocephalus ).

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.

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.

Rotavirus infection in children presenting with acute gastroenteritis in 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.

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.