Prevalence and type-specific distribution of human papillomavirus infection among women in mid-western rural, Nepal- A population-based study

Worldwide, the prevalence of human papillomavirus (HPV) 16 and or HPV 18 among women with low grade squamous Intraepithelial Lesions (LSIL), high-grade squamous intraepithelial lesions (HSIL) and cervical cancer is 25.8, 51.9 and 69.4% respectively [1]. The burden of HPV infection is significantly high about 10 million new cases of HSIL, and 30 million new cases of LSIL are diagnosed every year. The potential risk of HPV for cervical cancer is higher than Hepatitis B virus (HBV) is for liver cancer and even smoking is for lung cancer [2]. HPV infection is regarded as the well-established cause of cervical cancer now and a risk factor for other anogenital as well as head and neck cancers [1].

Cervical cancer is the most common cancer among women in Nepal. Cervical cancer demonstrates a decreasing trend in more developed countries, but consistently remains the number one female cancer of incidence and mortality in Nepal. According to the Information Center on HPV and Cancer (ICO), Nepal reports a prevalence of HPV 16 and or HPV 18 among women with LSIL, HSIL, and cervical cancer are 30.2, 63.4, and 80.3% respectively. The prevalence of HPV infection in Nepal is higher than in the world population [3–5].

Human genital HPV types are categorized according to the epidemiologic association and potential risk of cervical cancer. The eight most common types high risk (HR) HPV (HPV-16, 18, 31, 33, 35, 45, 52, 58) and relatively less common four types (HPV-39, 51, 56, 59) found in cervical cancer were classified in group 1. Probably carcinogenic to human’s HPV-68 was classified in group 2A. The remaining types of HPV 26, 53, 66, 67, 70, 73, 82 of the high-risk alpha species were classified in group 2B as “possibly carcinogenic” [6, 7].

The actual distribution of HPV is not known for some resource-limited countries, including Nepal [8]. Studies reporting the epidemiologic information on HPV in Nepal are sparse. Sherpa et al. in 2010 indicated that among the general population the overall prevalence of HPV was 8.6% including 6.1% for high-risk HPV [9]. Among the women with invasive cervical cancer, the incidence of HPV 16/18 infection was around 91% [9] and 70% [10]. Similarly, another study conducted by Shakya et al. [11] in the rural site of Kavre district found that the overall HPV prevalence was 14.4% including 7.9% of HR-HPV, whereas 9.6% of HR-HPV infection was reported in a study from far-western region of Nepal [12]. Furthermore, a study conducted by Bhatta et al. in 2017 among Nepali and Bhutanese women living in eastern Nepal reported the prevalence of 8.9% HR-HPV infection [13]. In the presence of co-factors, persistent infection with an oncogenic HPV is necessary to develop cervical cancer [14]. Therefore, the HPV test has emerged as an essential screening tool. HPV infection status is thus significant in cervical cancer screening and prevention strategy [15, 16].

Reproductive health indicators in Jumla are below the level than general Nepali women. The prevalence of female adolescent marriage is almost 83%; the total fertility rate is 4.2, literacy among women is 41% in Jumla [17, 18]. The population based epidemiological data of HPV in the general population in most parts of the country is still unknown [11]. So far, we know this was the first population-based study conducted in such remote area, Jumla. The objective of this study was to assess the prevalence and type-specific distribution of HPV infection and association of abnormal cytology with high-risk HPV infection among apparently healthy women in mid-western rural, Nepal. This study intends to give a sound basis for future strategic plans for the prevention of cervical cancer.

A well-established fact is that HR-HPV has a vital role in cervical cancer, which induces transformation of cervical epithelial cells into precancerous lesions and slowly into cancer [21]. About 84% of the cervical cancer burden is in the developing countries and especially in low resource areas. Though cervical cancer is the most common female malignancy in Nepal, a lack of proper prevention strategies exists to curb cervical cancer through screening, early treatment or vaccination. No effective screening programs have been established. However, some progress has been observed recently.

This study revealed prevalence rates of HPV infections (19.7%) and HR-HPV (11.7%). The HPV infection rate was higher in comparison to other previous studies done in Nepal which ranged from 8.6 to 14.4% [9, 11–13]. The findings of this study represent higher than the worldwide HPV prevalence of 10.4% and the corresponding estimate of 8.0% in Asia [22]. The higher incidence of HPV in Jumla may be attributed to the following risk factors: higher proportion of younger participants (age of 20–29 years participants were 40.4% of the sample), early marriage (marital age of 91% of the women was ≤20), multiple numbers of pregnancies, multiple children, risky sexual behaviors (multiple marriages, many sexual partners, higher proportion of sexually transmitted infections). Moreover, another important reason for the higher prevalence of HPV was probably due to the detection of HPV L1 gene by PGMY 09/11 primer system, which is more sensitive than GP5+/6+ or MY09/11 and able to amplify a spectrum of more than 30 genital HPV types [23]. Most of the studies conducted in China stated the prevalence of HPV was higher and varied by region ranging from 18.42 to 31.94% while in India reported a relatively lower rate (2.4 to 14%) [3, 24].

The highest prevalence of HR-HPV infection was in women of 20–29 years of age. The rate of HR-HPV infections declined with age, which is similar to a finding with a previous study [25]. In contrast to this study, a report from the rural area of China reflected HR-HPV and HPV 16/18/45 were at the peak in the age group of 55–59 years [26]. We also observed that the proportion of HR-HPV infection was higher among the women who had multiple children (p = 0.039) and multiple pregnancies (p = 0.029). Illiterate women tend to have a slightly elevated rate of HR-HPV infection compared with women who are literate, but there was no statistical significance. Previous studies have reported that high-risk sexual behavior such as multiple sexual partners is a critical factor of HPV infection in women [27], which is similar to the present study findings. Early marital age before 19 years was weakly associated with HR-HPV infection (p = 0.483). Though there were few cases of HIV positive participants, there was a strong association with HR-HPV infections, which was statistically significant (p = 0.007). The findings are similar to a previous report [28].

In Jumla, the HPV 16 is the most common genotype followed by HPV 39. HPV 18 was in 6th position in the order. The top five HR HPV genotypes in this sample were 16, 39, 58, 33 and 51. However, a study conducted by Bhusal et al. among 44 women diagnosed with invasive cervical cancer found HPV16 was the most common HR-HPV followed by HPV18 [10]. Sherpa et al. reported the most common high-risk types among women with normal cytology were HPV16, 58, 56, 18, and 52. Meanwhile, Shakya et al. reported HPV-18, 51, 59, 31 and 16 as the five most common HPV [9, 11]. So, it is clear that there are variations in the prevalence of HPV infection frequency within Nepal. Nevertheless, HPV 16 and 18 seem to be the most common. In the South Asian, HPV 16 is the most frequently detected genotype followed by HPV 58 while HPV 18 is common in Western countries. Other common HR HPV reported in the South Asian countries are 52, 18, and 31 in different orders of frequency [29, 30]. Worldwide, the most common HPV types in women are 16, 18, 31, 58, and 52, which is about 50% of all HPV infections [22].

Two types of vaccine against HPV are licensed for use in the United States by the FDA. A commonly used quadrivalent vaccine, Gardasil® covers against HPV types 6, 11, 16, and 18. A newer vaccine, Gardasil 9, was approved by the United States Food and Drug Administration (US FDA) in 2014 and protects against HPV types 6, 11, 16, 18, 31, 33, 45, 52, and 58 [31]. A pilot vaccination program was launched among 1096 school girls in Nepal giving quadrivalent human papillomavirus (types 6, 11, 16, 18) recombinant vaccine (Gardasil; Merk & Co.). A post-vaccine study reported the vaccine was safe with high acceptability in Nepali school girls but needed longer follow up to determine the long term vaccine effect [32]. Based on our findings even Gardasil 9 would cover only around 64% of women of Jumla since it does not include HPV 39, which was the second most common genotype in the present study sample. Therefore, from the ‘cost and benefit’ point of view, vaccination is not an ideal option in low resource countries. Thus, a simple, acceptable and sustainable screening method for cervical cancer screening provides greater efficacy.

The findings of this study suggest that abnormal cytology is strongly associated with HR-HPV infection. When the severity of disease is higher from LSIL to SCC, HR-HPV the infection rate also increased from 25 to 75%. The trend and percentage of the current findings are similar to previous studies [3, 11].

As a cross-sectional study, the prevalence of HPV infection in the rural region was obtained. Further longitudinal studies are recommended to study the relationship of the persistence HPV infection and other co-factors such as early marriage (early sexual debut), multiple pregnancies, multiple numbers of children, “chaupadi” tradition (poor harmful practice during menstruation), smoking, risky sexual behaviors and low socioeconomic status with anogenital cancers. Purposive sampling technique was used to collect a sample from the participants in a cervical cancer screening camp. Thus, the sample in this study may not be a reflection of all the Nepali women. However, the results provide valuable preliminary information on overall HPV prevalence and distribution of HR-HPV Genotype in a rural population.

Women living in a mid-western rural region of Nepal reflect a higher prevalence of HR-HPV infection than other areas of Nepal. This study provides preliminary information on overall HPV and type-specific HR-HPV prevalence; HR-HPV 16, 39, 58, 33, 51, and 18 are the most prevalent genotypes in this region. The data contribute to the epidemiological knowledge about HPV and type-specific HR-HPV genotypes prevalence in mid-Western Nepal.