Date Published: March 20, 2019
Publisher: Public Library of Science
Author(s): Gaythri Thergarajan, Suresh Kumar, Subha Bhassu, Sharifah Faridah Binti Syed Omar, Sanjay Rampal, Pierre Roques.
Increasing incidences of dengue have become a global health threat with major clinical manifestation including high fever and gastrointestinal symptoms. These symptoms were also expressed among Blastocystis sp. infected individuals, a parasite commonly seen in human stools. This parasite has been previously reported to replicate faster upon exposure to high temperature. The present study is a hospitalized-based cross-sectional study involved the collection of faecal sample from dengue patients. Stool examination was done by in vitro cultivation to isolate Blastocystis sp. Growth pattern of all the positive isolates were analyzed to identify the multiplication rate of Blastocystis sp. isolated from dengue patients. Distribution of Blastocystis sp. among dengue patients was 23.6%. Dengue patients who were positive for Blastocystis sp. infection denoted a significantly higher fever rate reaching 38.73°C (p<0.05) compared to the non-Blastocystis sp. infected patients (38.44°C). It was also found that Blastocystis sp. infected patients complained of frequenting the toilet more than five times a day (p<0.05) compared to those who were non-Blastocystis sp. infected. At the same time, the duration of hospitalization was significantly longer (p<0.05) for Blastocystis sp. infected dengue patients compared to the non-Blastocystis sp. infected patients. Besides, Blastocystis sp. isolated from dengue patients (in vivo thermal stress) showed a higher growth rate compared to the non-dengue isolated which was exposed to high temperature (in vitro thermal stress). Our findings suggest that presence of Blastocystis sp. during dengue infection could trigger the increase of temperature which could be due to highly elevated pro inflammatory cytokines by both parasitic and virus infection. This could justify why the temperature in Blastocystis sp. infected dengue patients is higher compared to the non-Blastocystis sp. infected patients. Higher temperature could have triggered a greater parasite multiplication rate that contributed to the aggravation of the gastrointestinal symptoms.
Blastocystis sp. one of the most widespread and prevalent intestinal parasite in humans has been shown previously to be polymorphic with diverse reproductive processes . The parasite has been distributed widely with prevalence varying between 0.19% and 100% in some cohort groups [2,3]. Sampling populations and differences in the diagnostic approaches could be the contributing reasons for the variation in prevalence . The prevalence of Blastocystis sp. infection among the urban and rural communities of Malaysia is 3.40% and 40.7%, respectively [5,6]. The parasite is known to cause bloating stomach, diarrhea, and other gastrointestinal symptoms . Both dengue and Blastocystis sp. infection have shown gastrointestinal symptoms but yet till to date there has been no study on the prevalence and correlation of Blastocystis sp. infection in dengue patients.
Continuous culture examination showed that 21 samples were positive, revealing a distribution of 23.6% Blastocystis sp. infection among dengue patients. The genomic DNA of these 21 positive samples were harvested and further subtyped. Sequence analysis categorized positive samples into four subtypes, subtype 1 (7 = 33.33%); subtype 3 (10 = 47.62%); subtype 4 (3 = 14.29%), and subtype 6 (1 = 4.76%). Approximately 14 variables have been analyzed including age, gender, race, lifestyle, having pet, history of dengue among family, symptoms (abdominal pain, diarrhea, flatulence, blood in stool), stool form, frequency of going toilet, day of illness, clinical diagnosis, temperature, whole blood count, and platelet count. However, only the notable ones have been highlighted in this paper. The general information of all the 89 patients who participated in this study has been tabulated in Table 1 based on the presence and absence of Blastocystis sp. infection.
Blastocystis sp. in in vitro cultures showed a higher growth rate with a corresponding increase in temperature . This concurs with our current observation where Blastocystis sp. isolated from dengue patients showed a higher growth compared to the parasites maintained in in vitro cultures at 37°C. Dengue patients infected with Blastocystis sp. also showed a significantly higher temperature compared to the non-Blastocystis sp. infected patients. This can be explained by the role of pro inflammatory cytokines in immune regulation during infection. Upon exposure to viral infection (i.e. dengue virus), white blood cells secrete chemicals known as pyrogens. These pyrogens by flowing in the bloodstream make their way to the hypothalamus, which in charge of regulating body temperature. When pyrogens bind to certain receptors in the hypothalamus, body temperature rises in the attempt of killing the invading pathogen. Some common pyrogens are known as Interleukin- (IL-) 1, 6, and tumor necrosis factor alpha (TNF-α). Moreover, various studies have reported that Blastocystis sp. enhance the production of pyrogens in various circumstances. Our previous study showed that IL-6 and IL-8 secreted by Blastocystis sp. antigen enhanced the cancer cell growth [24,25] which concurred with another study in Singapore where it was revealed that Blastocystis sp. antigens stimulate the production of a variety of cytokines, such as IL-1β, IL-6, and TNF-α . Apart from that, these pro-inflammatory cytokines were also found higher in the plasma and peripheral blood mononuclear cells of IBS patients [27,28]. These findings imply that the presence of Blastocystis sp. during dengue infection triggers the increase of temperature which could be due to highly elevated pro inflammatory cytokines by both parasitic and virus infection. This could justify why the temperature in Blastocystis sp. infected dengue patients is higher compared to the non-infected ones which triggers a greater parasite multiplication rate and causing the aggravation of the gastrointestinal symptoms.
As this study is the first to assess the prevalence of Blastocystis sp. infection among dengue patients, further research need to be carried out to determine the direct correlation between Blastocystis sp. and dengue infection. Firstly, the severity of dengue symptoms should be correlated with presence of Blastocystis sp. infection. Second, it is also important to make correlation between different age groups, as this can influence the susceptibility towards dengue and Blastocystis sp. infection in both adult and pediatric population. Lastly, dengue patients positive with Blastocystis sp. infection should be treated to assess whether the gastrointestinal symptoms especially severity of diarrhea and other symptoms can be reduced or eliminated.