Oyewale Tomori

Yellow fever vaccination and pregnancy: a four-year prospective study

During an outbreak of yellow fever (YF) in Nigeria in 1986-1987, women at various stages of pregnancy were vaccinated against YF, either because those pregnancies were not known at the time or because they requested vaccination out of fear of acquiring the disease. This offered an opportunity to assess the safety and efficacy of YF vaccine in pregnant women and the effect of this vaccine on their newborn children. Pre-vaccination and post-vaccination serum samples from the vaccinated pregnant women were tested by enzyme-linked immunosorbent assay and by neutralization tests for antibody to YF virus. The results showed that the antibody responses of these pregnant women were much lower than those of YF-vaccinated, non-pregnant women in a comparable control group. Follow-up of these women and their newborn children for 3-4 years showed no abnormal effect that could be attributed to the YF vaccine, which suggests that vaccination of pregnant women, particularly during a YF epidemic, may not be contraindicated.

Urban yellow fever epidemic in western Nigeria, 1987

A large epidemic of urban yellow fever occurred in April and May 1987 in Oyo State, western Nigeria. The principal vector was Aedes aegypti, breeding in domestic water containers. The 1987 outbreak followed an epidemic of sylvatic yellow fever in eastern Nigeria the previous year, and probably resulted from introduction of the virus by viraemic travellers. The outbreak in Oyo State ended in early July, by which time 805 cases and 416 deaths had been officially notified. However, surveys of 3 villages in the epicentre, a region with over 4 million inhabitants, indicated an infection rate of approximately 20%, a clinical attack rate of 2.9% and a mortality rate of 0.6%, suggesting that the true incidence of cases and deaths far exceeded the official reports. Yellow fever virus was isolated from persons with fully developed yellow fever as well as mild febrile illness. One virus isolate was made from blood of an individual with mild illness, who had received 17D vaccine 5 d earlier; monoclonal antibody analysis showed that the isolate was a wild-type virus. Larval indices of Ae. aegypti were very high; however, low vector competence of the Ae aegypti population may have provided a constraint on spread of the epidemic. In late 1987 a third epidemic appeared in Niger State, northern Nigeria, with 644 reported cases and 149 deaths. The vector(s) involved is (are) unknown.

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 ).

A survey for antibodies to Lassa virus among health workers in Nigeria

A study was conducted among 552 health workers at 6 health facilities in Nigeria. Lassa virus immunoglobulin (Ig) G antibody was detected in 12.3%, using an enzyme-linked immunosorbent assay. Antibody prevalence in the 6 health centres ranged from 1.2% to 27.3%. Prevalences were higher in primary and secondary health facilities than in tertiary centres. Seroprevalences ranged from 1.7% to 23.7% among different occupational groups of health workers; the highest observed antibody prevalence was among ward aids. Lassa virus IgM antibody, indicating recent infection, was present in 6 of the health workers, 5 of whom were ward aids and one was a nurse. All of the health workers with specific IgM came from a single facility in Lafia, sampled during an outbreak of Lassa fever.

Bluetongue and related viruses in Nigeria: Experimental infection of West African dwarf sheep with Nigeria strains of the viruses of epizootic haemorrhagic disease of deer and bluetongue

Abstract West African dwarf sheep were inoculated by the subcutaneous route with epizootic haemorrhagic disease of deer (EHD) virus or bluetongue (BT) virus. No clinical disease was observed following primary EHD or BT infection, or subsequent challenge with either homologous or heterologous virus. However, viraemia was detected in non-immune sheep exposed to BT virus, but not in BT- or EHD-immune sheep challenged with either virus, or in non-immune sheep exposed to primary EHD virus infection. Complement fixing antibodies developed against both EHD and BT viruses following the primary infection with either virus, or subsequent challenge with homologous or heterologous virus. Following a primary infection, virus-neutralising (VN) antibodies developed only against the inoculated virus, while the detection of VN antibodied to both viruses followed the challenge of an EHD- or BT-immuned sheep with either the homologous or heterologous virus. These findings further support previous reports of a relationship between EHD and BT viruses. between EHD and BT viruses.

Wild life rabies in Nigeria: experimental infection and transmission studies with the shrew (Crocidura sp.).

Wild caught shrews were infected with rabies virus strains by the intramuscular, subcutaneous and oral routes. Inoculated animals became sick within four to seven days of inoculation with characteristic dumb rabies symptomatology. The significant symptom was a progressive loss of aggressiveness and an unbalanced gait. The course of illness was 36-48 hours. Transmission of rabies virus to susceptible laboratory mice was successful only with shrews which had been infected orally and allowed to bite adult mice soon after infection. This suggests a mechanical role in the transmission of rabies. Virus was isolated only from shrews infected with street or wild strains of rabies, but not with vaccine or fixed rabies strains.

Circulation of poliovirus among risk groups in Ibadan, Nigeria.

Faecal samples collected from 114 fully vaccinated pre-school children and 32 unvaccinated infants in Ibadan, Nigeria, were assayed for poliovirus in Hep-2 and RD cell cultures. 8 strains of poliovirus type 1 were isolated from 146 samples--3 from 32 unvaccinated children aged less than 40 d and 5 from 114 fully vaccinated children aged between 9 and 60 months. Studies using Sabin and wild monoclonal antibodies and the polymerase chain reaction confirmed 7 of the 8 isolates to be of the wild type, a possible source of infection among vaccinated children.

Tataguine virus isolations from humans in Nigeria, 1971–1975

Abstract Seven isolates of Tataguine virus were obtained from Nigerians between 1971 and 1975. All were from children less than five years old. The virus is more active in the early wet season. Clinical presentation is similar to malaria.

Response of Erythrocebus patas monkeys to experimental infection with the orbivirus Orungo virus

The response of Erythrocebus patas monkeys experimentally inoculated by the intravenous and subcutaneous routes with Orungo virus (family Reoviridae, genus Orbivirus) was studied with reference to development of clinical signs, circulation of virus and antibody response. None of the animals showed clinical disease nor did they circulate virus. However, all the animals developed complement fixing (CF), neutralizing (N) and agar gel (AG) precipitating antibodies between day seven and day 14 post infection (p.i.). The CF antibodies appeared earlier and lasted for a longer period than did the N antibodies. The presence of transient 2-mercaptoethanol (2-ME) sensitive CF antibodies was demonstrated in sera collected between day seven and day 14 p.i. The significance of these findings in the interpretation of serological surveys in man for Orungo virus antibody is discussed.