Blood is a biologically active material. A spectrum of blood-borne infectious agents is transmitted through transfusion of infected blood donated by apparently healthy and asymptomatic blood donors. The diversity of infectious agents includes hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency viruses (HIV-1/2), human T-cell lymphotropic viruses (HTLV-I/II), cytomegalovirus (CMV), parvovirus B19, West Nile Virus (WNV), dengue virus, trypanosomiasis, malaria, and variant CJD.[20
The seroprevalence found in this study (39.9%) of North Indian blood donors is lower than the prevalence reported from developed countries such as Europe[12
] and England[13
] but higher than that of Singapore 16.2%.[16
] In most of the countries, B19 virus infection occurs during childhood and by the age of 15 years, approximately 50% of children have anti B19 antibody. B19 prevalence may further increase during lifetime and reach values higher than 85% in elderly. In another study the North African population was reported to have a prevalence of 64% and the Belgian population had a prevalence of 75%.[15
] The prevalence in Japan was found to be 55% by ELISA testing using monoclonal antibodies and viral antigen[22
] and after outbreaks of erythema infectiosum the rates varied.[23
] Though the trend of prevalence did not differ much in India also, the lower prevalence in elderly age group was found. The explanation to this finding could be due to the fact that the maximum age of donors in this study was 60 years and thus the prevalence in still older people was not studied. India being a tropical country with long duration of summer season and with high temperature, it may not be suitable for the transmission of virus during this season. In the colder countries where epidemics of viral infection have been observed it occurred during winter season.[18
Since the Drugs and Cosmetic act of India does not allow accepting donors less than 18 years and more than 60 years of age for blood donation, the age range was in this limit only. The reason for most donors being young is that in India most of the donations are from close relative as replacement donors and the persons in younger age group being young and in better health take the responsibility and donate blood. The total number of female donors is small in this study due to several reasons. In our hospital most of the patients are referred from distant rural and urban are as for tertiary care and in India males are the ones who accompany the patients and are available for blood donation. Among females who do come forward for blood donation about 70% were rejected, with most common cause for deferral being anemia (23%) followed by low body weight (<45 kg; 7.5%) and lactation or pregnancy (2.6%). The reason for male preponderance to B19 IgG antibodies positivity could also be explained by the fact that in India males are more exposed to occupational hazards as they are the working and earning members of most Indian families. In this study the prevalence was 40% in the males of age group 18-30 years, 38.5% in the age group 30-40 years, 46.03% in age group 40-50 years, and 52% in the age group 50-60 years. In a study from Japan it was demonstrated that the antibody positivity rate was approximately 40% among younger donors (16-20 years), gradually increased among middle-aged men (30-39 yr.) and reached its highest levels (80%) among older donors (>50 years of age).[19
] We have found similar results in younger donors but the prevalence in older donors is not so high. This could be probably due to the age limitation (up to 60 years) in our study group. Moreover, India is a tropical country while Japan is a colder country. Increased prevalence has been observed in countries with temperate climate from winter to early summer season. Parvovirus prevalence was not affected by marital status of the donors as was expected, since the sexual route does not spread this infection.
World Health Organization (WHO) proposed a definition of standards of living “Income, occupation, standard of housing, sanitation, nutrition and the level of provision of health, educational, recreational, and other services may all be used individually as measures of socioeconomic status and collectively as an index of the standard of living.” Keeping the above variables in mind the association of the prevalence of anti-B19 IgG antibodies and socioeconomic status of the subjects was established. The higher positivity among manual labors including farmers could be explained by their poor living conditions such as poor housing overcrowding poor income and low education levels. The outdoor activities could lead to more exposure and thus contact with infectious agents and could be a reason for higher prevalence among this occupational group. No previous study has been done to define parvovirus prevalence in terms of socioeconomic status of blood donors; however, considerable work needs to be done in this regard. Education is a major factor influencing health status. The world map of literacy closely coincides with the maps of poverty, malnutrition, ill health, and high mortality rates. Studies have indicated that education, to some extent compensates the effects of poverty on health, irrespective of the availability of health facilities. In this study also illiteracy and low education levels had similar influence on the prevalence rate.
Large family size and small house size were important variables affecting the prevalence of B-19 IgG antibodies. Most of our donors had large family size with more than six members in each family (60.8%). It is not an uncommon occurrence in a populous country like India where joint family systems exist and overcrowding invariably occurs in quite a lot of households. Overcrowding leads to a higher and faster spread of infection through the respiratory route.
Thus, it was found that the prevalence of anti-B19 IgG antibodies is significantly higher in individuals with poor standards of living and low socioeconomic status. To the best of our knowledge, this is the first study of this kind in India. Since mainly respiratory droplets spread parvovirus B19, similar trends have been documented in the epidemiology of communicable diseases spread through respiratory route such as diphtheria, rubella, influenza, pertusis, meningococcal meningitis, and tuberculosis. The risk of exposure is greater in lower social classes, living in overcrowded and poor housing conditions. The lack of education, large families, and poor qualities of life are the predisposing factors for such infections. Blood-borne infections like hepatitis B are also influenced by the socioeconomic status. The prevalence is lowest in areas of high standards of living (Australia, Europe) and highest in countries of areas with poor socioeconomic status and living conditions (China, South East Asia). Epidemiological studies have shown that health and disease is not equally distributed in social classes. Individuals in upper social classes have longer life expectancy and better health than those in lower social classes, but certain diseases such as diabetes, coronary heart disease, and hypertension are more common in the former group. Social class difference has also been observed in utilization of health care services; however, social classification varies from country to country.
In this study, the observation of a significantly higher prevalence in the winter season could be related to the preferential occurrence of epidemics during winter or spring in temperate climates and points to a more effective air-borne transmission of virus at colder temperatures.[13
] Since the span of this study was 9 months, the epidemiology of seasonal variation in summer months could not be studied.
The incidences of viraemic blood donors prior to PCR-based assays were reported to be very low, about 1 in 30,000 to 50,000. Now with advancements in PCR assays and especially nested-PCR, the incidence of B19 viraemia has been found in 0.03% to 0.6% and even higher percentage of blood donors.[24
] This frequency is sufficient to contaminate plasma pools used in preparation of factor VIII or IX concentrates. Thus multi-transfused hemophiliacs receiving factor concentrates are likely to be greatest victim of transfusion-transmitted B19 infection. Lastly, it should be borne in mind that seropositive donors are immune and the donor unit contains neutralizing antibodies.
More than 25 years after the discovery of the parvovirus B19, the issue of the safety of blood components and the screening of this virus in blood donations is still debated. However, the existence of persistently B19-infected individuals carrying B19 DNA despite the presence of specific IgG (estimated at 1% of blood donors) could constitute a potential threat for transfused immunocompromised recipients.[26
] The screening of such donors, which could be performed through a very highly sensitive NAT (nucleic acid amplification test), would be justified only if the infectivity of such blood donations is demonstrated. If not, a screening of blood donors positive for B19 IgG would be a sufficient preventive measure.[27