Bats, Chiroptera, have long been postulated to play an important role in Arthropod suppression, seed dispersal, and pollination. The rich diversity in bat dietary habits assists in maintaining ecosystem health. In Bangladesh, 31 Bat species are found, three of which are fruit-eating. Of all frugivorous Bats, Pteropus medius and Rousettus leschenaultii are common and widely distributed in the country. The False Vampire Bat, Megaderma lyra, largest of the insectivorous Bats, is also quite common and widespread in Bangladesh. Bats are associated with zoonotic transmission of Viruses including Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), and Middle East Respiratory Syndrome Coronavirus (MERS-CoV), as well as the Ebola, Nipah, and Hendra Viruses, as well as disease-causing Protozoa like Plasmodium sp., Hepatocystis sp., Nycteria sp., and Polychromophilus sp. Among nine Hemosporidian genera, are Hepatocystis, which infects a wide range of hosts including Primates, Bats, Ungulates, and Rodents, in addition to Plasmodium, the causitive agent of Malaria in a wide range of Mammals. Parasites of seven other Haemosporidian genera, however, have been found exclusively in Bats, emphasising that they might harbor the most diverse set of Haemosporidian parasites within the Mammalian clade. The prevalence of Haemosporidian parasites among fruit and insectivorous Bats has been detected previously to be 40% among Bats from West Africa. Hepatocystis sp. was identified from a species of Flying Fox, Pteropus hypomelanus, in Southeast Asia, displaying an unusually high diversity and is also prevalent in Epauletted Fruit Bats, Epomophorus wahlbergi, in West Africa.
In light of these findings, Bats have been identified as possible reservoirs of Haemoprotozoa. They are included in epidemiological surveys, and particularly for the detection of Bat-specific blood Protozoa. Due to the gross destruction of habitat with rapid urbanisation, contact between Human and Bats is showing an increasing trend. Frugivorous Bats usually suck the juice of fruits instead of eating the whole fruits. They may play an important role in the transmission of infectious agents to rural communities, particularly small children, who collect those Bat-wasted fruits. In addition, ectoparasites which feed on Haemoprotozoa-infected Bats, could serve as a route of transmission to Humans. The potential public health threats posed by Bats thus suggests the importance of studying Haemoprotozoa towards its proper control and better management of Human diseases related to Bats. Maximum research has led on emerging Viruses in Bats; however, Bacterial and parasitic agents in Bats have been least studied and most neglected.
In a paper published in the Journal of Threatened Taxa on 26 July 2020, Shariful Islam of the Institute of Epidemiology, Disease Control and Research, and the EcoHealth Alliance, Rakib Uddin Ahmed of the Faculty of Veterinary Medicine at the Chattogram Veterinary and Animal Sciences University, Mohammed Kaisar Rahman and Jinnat Ferdous, also of the Institute of Epidemiology, Disease Control and Research, and the EcoHealth Alliance, Mohammed Helal Uddin, Sazeda Akter, Abdullah Al Faruq, and Mohammad Mahmudul Hassan, also of the Faculty of Veterinary Medicine at the Chattogram Veterinary and Animal Sciences University, Ausraful Islam of the International Centre for Diarrhoeal Disease Research, and Ariful Islam, once again of EcoHealth Alliance, present the results of a study which aimed to aimed to gain a better understanding of parasitic pathogens in Bats, by conducting a study to identify the Haemoparasites of Bats in Bangladesh.
As part of a larger study through the United States Agency for International Development Emerging Pandemic Threats PREDICT project and associated Ecology of Nipah Virus survey, Islam et al. captured Bats in seven districts within or near Human settlements across Bangladesh. A total of 533 Bats (377 Pteropus medius, 111 Rousettus leschenaultii, and 45 Megaderma lyra) blood samples were collected randomly from Bats during 2010 and 2013. The methods of Bat were identified by species, age, weight, sex, physiological, and reproductive status. The Bats were released immediately after sample collection.
Nine percent of the total sample was found to be positive for Haemoprotozoa. The overall prevalence of Haemoprotozoa was 5%, 13%, and 29%, respectively in Pteropus medius, Rousettus leschenaultii, and Megaderma lyra.
In Pteropus medius, Babesia sp. was found at the same percentage in both sexes (3%), Hepatocystis sp. was found higher in females (3%). The prevalence of Babesia sp. was higher in adults (4%) while Hepatocystis sp. prevalence was higher in neonates (6%). Both Babesia sp. (4%) and Hepatocystis sp. (3%) prevalence were higher in peri-urban area compared to rural settings. In Megaderma lyra, male were more infected (25%) by Babesia sp. than females (16%) whereas Hepatocystis sp. infection was higher in females (12%) than in males (5%). On the other hand, Babesia sp. infection is more prevalent in adult Megaderma lyra (20%) and bats of rural areas (20%) than Hepatocystis sp. (9%). In case of Rousettus leschenaultii, Babesia sp. infection was higher in males (13%) than in females (6%) but Hepatocystis sp. was found to be at higher percentage in females (4%) than males (2%). Juveniles were more prone to Babesia sp. (13%) than adult Bats (8%). No Hepatocystis sp. infection was found in juveniles. In rural areas, Babesia sp. infection was more frequent (10%) than Hepatocystis sp. (2.7%). No associations, however, were found to be statistically significant.
To Islam et al.'s knowledge, this is the first study to report the prevalence of Haemoprotozoa in the Bats of Bangladesh. The study identified Babesia sp. and Hepatocystis sp. in three different Bat species. The identified Haemoparasites in Bats are similar to other reports from Bats globally. Bats have harbored a diverse set of Haemosporidian species for centuries and Hepatocystis was found to be at a high endemic level in Pteropodidae. Although the identified parasite species have not been associated with public health implications, there is evidence of co-infection of Primates and crossing of the Primate barrier by Hepatocystis sp. Furthermore, some of the Haemosporidian species from Bats resemble Rodent Mammalian parasites. The potential for Bat-Human, Bat-Rodent-Human, and Bat-Arthropod-Human cross-species transmission of Haemoprotozoa is not known but warrants further investigation, particularly as the Bat species included in the study are native to Bangladesh and share habitat as well as food and water sources with Humans, suggesting potential plausible routes of accidental transmission.
The overall prevalence of blood Protozoa (9%) was lower than that of earlier reports from various countries. Haemoparasites in Bats can be found as a result of feeding habits (e.g. feeding on Insect vectors from which they may acquire the Haemoprotozoa). The prevalence of Babesia canis in Bats was reported as 2.7% in a 2015 study of Bats in Hungary and the Netherlands, which is much lower than Islam et al.'s study. Other studies reported 50% and 23% prevalence of Babesia sp. in bats from Britain. Most of the previous studies identified Babesia vesperuginis in Bat species throughout the world. The role of Bats in the ecology of Babesia sp. and the vectors involved in transmission of Babesia sp. among them warrants further investigation. In Islam et al.'s study, the Protozoa were identified up to the level of genus. Hepatocystis sp. prevalence was lower in this study than in a previous study in Malaysia. These findings, however, may vary due to the study area, duration of the study, resistance of Bats and lack of Bat Fly vectors in Bangladesh.
Infection with Babesia sp. was higher in males (Megaderma lyra and Rousettus leschenaultii) whereas in case of Hepatocystis sp. the prevalence was higher for females. These differences can be attributed to variation in behavior, feed composition, and body mass between sexes. Besides, the sex hormone, testosterone increases the susceptibility to parasitism. Moreover, parasite development and transmission is favoured by the colonial habits of females. Adult Pteropus medius had higher Babesia percentage than juvenile, may be due to increased growing host age. Young animals are less susceptible to Babesia due to inverse age resistance. But the same Haemoparasite was higher in juvenile Rousettus leschenaultii which can be attributable to the ability of the parasite’s vertical transmission. Hepatocystis was higher in juvenile Pteropus medius, because they have low body mass, naive immune system, and nearly no anti-parasite behavior. The pattern of parasitism in Bats, however, should be explored in-depth in future studies.
Islam et al. report a survey of Haemoparasites in Bats undertaken over three consecutive years at habitat fragmented landscape in Human settlements areas in Bangladesh, where the prevalence and diversity of Bat-infecting Haemosporidian parasites have not been studied before. Molecular screening should be undertaken in future to overlay data in the microscopy with those from molecular biology. Molecular characterisation is the only way to definitively confirm the species of a Haemoparasite. The findings, however, remain of great interest. Further studies are needed to determine the species of parasites harbored in Bats of Bangladesh.
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