Parvovirus B19: Evaluation of Incidence, Prevalence and Risk Factors among Pregnant Women Attending Ante-Natal Clinic in Nasarawa State, North Central of Nigeria

Trans-placental transmission of parvovirus B19 during pregnancy has been reported as one of the leading causes of non-immune fetal hydrops, spontaneous abortion or intra-uterine fetal death. We therefore set out to determine the presence of parvovirus B19 (IgG and IgM) antibodies and their risk factors among pregnant women attending ante-natal clin ic, at Federal Medical Center, Keffi, Nasarawa State, Nigeria.A total of 273 pregnant women (Age range 15-40 years) participated after informed consent and clearance from the research ethics committee. Each filled a self-administered questionnaire and donated blood samples between January and August 2012. A recombinant parvovirus B19 IgM and IgG ELISA kit from DeMediTec (USA) was used for the assays.Of the 273 participants, 36 (13.2 %) had IgM antibodies, while 75 (27.5%) had IgG antibodies with those aged 15-20 and 36-40 years having the highest incidence and prevalence rates. Being a house wife, having more ch ild ren and histories of blood transfusion, miscarriage and still b irth were associated with infection (P < 0.05).The study reveals high incidence and prevalence of parvovirus B19 infect ion among the pregnant women. The presence of parvovirus B19 IgM antibody particularly in the first and second trimesters of pregnancy poses the danger of likely trans placental transmission leading to spontaneous abortion and intra-uterine fetal death.


Introduction
Hu man parvovirus B19 is the only known parvovirus pathogenic to human [1,2]. The in fection during pregnancy may account for thousands of incidences of fetal loss per annum in Eu rope, North A merica and beyond [3].
Trans-placental transmission of parvovirus B19 during pregnancy is one of the leading causes of non-immune fetal hydrops, spontaneous abortion or intra uterine fetal death [4,5]. The disease which was first discovered in 1975 [6] was first associated with disease in 1981, when it was linked to aplastic crisis, fifth disease, spontaneous abortion and some form of acute arthrit is [7]. It also has a 33% vertical transmission rate with a 2-3 incidences in all spontaneous abortion [8].
B19 may also stimu late a cellu lar p ro cess in itiating ap o p to s is [9 ] . Th is may ac co u n t fo r th e min imal inflammatory response noted in tissues infected with B19 [10].The virus infect ion of megakaryocytes, placental cells, fetal liver cells and myocardial cells results in anemia, which can lead to high output congestive heart failure, causing fetal circulatory compro mise. The risk of fetal demise is highest in the first trimester and is thought to be as high as 10% in wo men who are infected prior to 20 weeks of gestation [11]. The P blood group antigen, which serves as a receptor for B19, has been detected on cells of the villous trophoblast of placental tissues in varying amount during the course of pregnancy. And in the first trimester of pregnancy, the level of the P-antigen is very high. This high level of globoside receptor on placental cells in early pregnancy may act as a pathway fo r B19 to be transmitted fro m the mother to the fetus where by the virus can then infect erythroid progenitor cells for replication [12]. There are limited data on the incidence and prevalence of parvovirus B19 in Nigeria in spite of the importance of such data in health policy formulat ion. We therefore, undertook a survey to establish the incidence, prevalence and risk factors of this agent among pregnant women attending Plateau specialist hospital in Jos.

Study Area
The study was conducted in Nasarawa State. Nasarawa State is located in the north central geopolit ical zone of Nigeria. It lies between latitude 80 0 35 '

Study Population
This consisted of pregnant women attending ante-natal clin ic in Federal Medical Center, Keffi, between January and August, 2012. The hospital has an average of 70 pregnant wo men attending ante-natal clinic weekly and population of two hundred and seventy three (273) subjects participated in this study.

Ethical Considerati ons
Clearance fro m the health research ethical co mmittee of Federal Medical Center, Keffi was obtained in accordance with the code of ethics for b io medical research involving human subjects. Signed informed consent was also obtained fro m each of the subjects.

Exclusion and Inclusion Criteria
The study inclusion criteria were being pregnant, ante-natal clinic attendance records and signed informed consent; while the exclusion criteria included absence of pregnancy, age below 15 and above 40years and failu re to sign a consent form.

Speci men Collection
After collection of the signed informed consent form, and the self-ad min istered questionnaires with the relevant personal informat ion, 5mls of blood sample fro m each subject was aseptically collected by venipuncture of the cubital vein using disposable needles and syringes. The samples were collected between January and August, 2012, and then taken to Innovative Biotech Virology Laboratory where the sera were separated, put into sample v ials and stored at -20 o c until assayed.

Assaying Techni que
The DeMeditec parvovirus B19 IgM and Ig G (Reco mb inant) En zy me immunoassay kit[Lot; 123G/ K038] USA was used for the in-v itro qualitative and semi-quantitative determination of immunoglobulin class antibodies assay for parvovirus B19 in seru m, according to the manufacturer's instructions.

Interpretation of Results
Incidence was defined as the presence of IgM antibodies to parvovirus B19 in the tested subjects, while prevalence was defined as the presence of parvovirus B19 Ig G antibodies. The presences of IgM or Ig G antibodies were determined by comparing the absorbance value of each sample to that of the cut-off value. Specimens with absorbance values less than the cut-off values were recorded as negative while those above are recorded as positive according to the manufacturer's instructions.

Statistical Analysis
Pearson chi-squares were calculated and compared with values on a chi-square table at 95% confidence interval. P values ≤ 0.05 were considered statistically significant.

Results
Blood samples were collected fro m 273 p regnant women. The serum samp les were analyzed for parvovirus B19 (IgM and IgG) antibodies. Of the 273 samp les assayed, 36(13.2%) were positive for Parvovirus B19 IgM and 75(27.5%) for B19 Ig G. Figure 1 shows the distribution of parvovirus B19 antibodies according to age. The highest IgM antibodies (16.7%) and Ig G antibodies (37.5%) antibodies were observed in the age groups 15-20 and 36-40 years respectively, wh ile the lowest Parvovirus B19 IgM antibodies and IgG antibodies were observed in the age group 36-40 and 15-20 years respectively (P>0.05). Table 1 shows the distribution of parvovirus B19 antibodies according to gestational age. The highest IgM antibodies (13.3%) and Ig G antibodies (31.1%) were observed among pregnant women in their second trimester, followed by those in their first trimester. Those in their third trimester gave the least prevalence (For IgM, P>0.05 wh ile for Ig G, P=0.05). Table 2 shows the distribution of parvovirus B19 antibodies according to history of pregnancy complications (miscarriage and stillb irth). The highest IgM antibodies (20.0%) and Ig G antibodies (40.0%) were observed among those who have had history of both miscarriage and still b irth. The lowest IgM antibodies (10.5%) and Ig G antibodies (22.8%) were observed among pregnant wo men with no history of pregnancy complications (P>0.05). Table 2 shows the distribution of parvovirus B19 antibodies according to the number of children in the household. The highest IgM antibodies (19.5%) and Ig G antibodies (42.9%) were observed among those with 5 or more ch ildren. The lowest IgM antibodies (10.6%) and IgG antibodies (19.2%) were observed among those with 0-2 children (For IgM, P>0.05, while for Ig G, P<0.05). Pregnant Women Attending Ante-Natal Clinic in Nasarawa State, North Central of Nigeria Table 2 shows the distribution of B19 antibodies according to history of blood transfusion. The highest IgM antibodies (23.1%) and Ig G antibodies (30.8%) were observed among those who has been transfused with blood at one occasion or another, while the lowest IgM antibodies (26.9%) and Ig G antibodies (11.5%) respectively were found among those who have not received blood transfusion (For IgM, P<0.05, wh ile for Ig G, P>0.05). Table 2 shows the distribution of parvovirus B19 antibodies according to occupation of the subjects. The highest IgM antibodies (26.7%) and Ig G antibodies (40.0%) were observed among pregnant women who are housewives. The lowest IgM antibodies (7.4%) and Ig G antibodies (24.4%) were observed among those who are civil servants and business wo men respectively (For IgM, P<0.05, wh ile for Ig G, P>0.05).

Discussion
This study identifies an incidence (13.2%) and prevalence (27.5%) of parvovirus B19 at three tert iary health care institution in Nasarawa State,wh ich has an average of 70 pregnant women attending ante-natal clinic weekly. The incidence of 13.2% and prevalence of 27.5% agrees closely with the reports of Keikha et al in Iran who reported 10.3% incidence and 21.8% p revalence in pregnancy [14]. It also accords with the 30-50% range reported in India by Kaur and Basu, and also with 30-60% prevalence range reported in United States by the American Academy of Ped iatrics Co mmittee on infectious Diseases, [1,15]. Ou r finding is however, lower than the 63-71% prevalence range reported in Dublin, Ireland, by Eis-Hubinger, and the 70% reported in United Kingdom and Finland among adults by Masssong et al [16,17]. It is however very high co mpare to the 2.0% incidence among blood donors in North Africa (Tunisian) and Western Europe (Belg ian) reported by Letalef et al [18]. There is no clear exp lanation for this difference.
The incidence of parvovirus according to age groups was observed to decrease simultaneously with increase in ages while the prevalence was found to increase with increase in age groupings. This trend could be due to chances of exposure to the infection with age. A report of increase seroprevalence with age and greater than 70% in adult's populations was reported by Kerr et al, [19].
The outcome of the highest incidence (13.3%) and prevalence (31.1%) in the second trimester in the gestational age of pregnancy could probably be explained as susceptibility due to hormonal changes with progress in pregnancy. Since the presence of IgM antibodies signifies recent infection, it therefore poses the danger of transplacental transmission with the risk of fetal anaemia and demise highest in the first and second trimester especially for wo men infected prior to 20 weeks of gestation. A similar report was made by Markenson, and Enders et al [11,24].
The observation fro m the history of pregnancy complications, in wh ich those with both miscarriage and still birth experience a higher parvovirus B19 incidence and prevalence when co mpared with those with no such history, further emphasizes the possible outcome of the effect of parvovirus B19 infection during pregnancy.
The outcome of the incidence and p revalence of parvovirus B19 antibodies among those with more number of children as against those with few or no children, suggests the involvement of contact with mo re nu mber o f children as a possible source of spread of the infection. However, previous reports identified children are the main sources of transmission, and outbreaks can persist for months in schools and day care centers, due to the relatively large nu mber of seronegative children and close contact of children within this environment, [20,21]. A similar result was also reported by Xu et al, and Laura and Caraciolo [2,10]. The findings fro m our study was statistically significant at P<0.05.
The incidence and prevalence obtained among those who have had blood transfusion as against those who have not also emphasizes the possible implication of blood transfusion in the transmission of the infection, especially if there is contamination. This study identifies the incidence to be statistically significant at P<0.05. A report by Corcoran and Doyle, [3], observed that despite the fact that parvovirus B19 infection can be transmitted via contaminated blood products; there is presently no strict regulatory prerequisite governing B19 contamination of pooled plasma or blood products prior to products release.
The prevalence of B19 antibodies among housewives when considering the occupation of the pregnant women Pregnant Women Attending Ante-Natal Clinic in Nasarawa State, North Central of Nigeria studied, may imp licate household contact in the transmission of the in fection. Previous studies reported that, the infection is co mmonly passed through respiratory tract secretions from close personal contact [2]. Statistically, there was no significant difference between B19 incidence and occupation during pregnancy but there was significant difference between B19 p revalence and occupation. A report of no significant differences found in maternal infect ion fro m occupational exposures was reported by Harger et al [22], and Valeur et al [23].
The high incidence and prevalence of infection with B19 virus among the pregnant wo men and the known dangers posed in pregnancy raise transfusion policy questions in Nigeria. Like other b lood-transmissible viral infect ions, routine screening for B19 virus infection before transfusion should, as a matter of policy, be made co mpulsory in Nigeria.