The Mengla virus (Filoviridae: Dianlovirus)

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Introduction

Diseases associated with Marburg and Ebola filoviruses (family Filoviridae) pose a serious threat to public health due to their high mortality rate and ability to cause epidemic outbreaks [1, 2]. Since the discovery of the Marburg virus in 1967 and the Ebola virus in 1976, outbreaks of hemorrhagic fever have been repeatedly reported, mainly on the African continent, with cases of the virus being brought to Europe and the United States by infected medical workers [1–3].

The family Filoviridae was originally organized on the basis of combining genera corresponding to Marburg (Marburgvirus) and Ebola (Ebolavirus) viruses, based on common morphological characteristics and genome type and structure (single-stranded negative-sense RNA – ss(−)RNA). Based on these same genomic characteristics, the family was included in the order Mononegavirales, one of four orders (taxon above the family) that existed at that time. Currently, due to the development of molecular genetic and evolutionary approaches, the taxonomy of the family has been significantly expanded and refined and is as follows: Riboviria: Orthornavirae: Negarnaviricota: Monjiviricetes: Mononegavirales: Filoviridae. The genus Orthomarburgvirus (formerly Marburgvirus) includes two species, while the genus Orthoebolavirus (formerly Ebolavirus) now includes six species (Table 1). Most Marburg and Ebola viruses appear to be ecologically associated with various species of fruit bats (Chiroptera: Pteropodidae) living in Africa and Asia. An exception is the Bombalivirus (Orthoebolavirus bombaliense, Bombalivirus), whose RNA was detected in bulldog bats (Mopscondylurus) in Sierra Leone in 2018. Later, a new genus, Cuevavirus, was assigned to the family Filoviridae, represented by the Lloviu virus (Lloviuvirus), which was detected in samples from a colony of common bent-wing bats (Miniopterus schreibersii) that died in 2002 in Spain [3–7]. Thus, filoviruses may be ecologically associated not only with different species of fruit bats (fruit-eating flying foxes or flying dogs), but certain species of bats may also be involved in their circulation.

 

Table 1. The modern taxonomy of the family Filoviridae

Таблица 1. Современная таксономия семейства Filoviridae

Genus Род	Species Вид	Prototype virus Прототипный вирус
Cuevavirus	Cuevavirus lloviuense	Lloviuvirus [LLOV]
Dianlovirus	Dianlovirus dehongense	Déhóngvirus [DEHV]
	Dianlovirus menglaense	Menglavirus [MLAV]
Loebevirus	Loebevirus percae	Lötschbergvirus [LTBV]
Oblavirus	Oblavirus percae	Oberlandvirus [OBLV]
Orthoebolavirus	Orthoebolavirus bombaliense	Bombalivirus [BOMV]
	Orthoebolavirus bundibugyoense	Bundibugyovirus [BDBV]
	Orthoebolavirus restonense	Restonvirus [RESTV]
	Orthoebolavirus sudanense	Sudanvirus [SUDV]
	Orthoebolavirus taiense	Taï Forestvirus [TAFV]
	Orthoebolavirus zairense	Еbolavirus [EBOV]
Orthomarburgvirus	Orthomarburgvirus marburgense	Marburgvirus [MARV] и Ravnvirus [RAVV]
Striavirus	Striavirus antennarii	Xilangvirus [XILV]
Tapjovirus	Tapjovirus bothropis	Tapajósvirus [TAPV]
Thamnovirus	Thamnovirus kanderense	Kandervirus [KNDV]
	Thamnovirus percae	Fiwivirus [FIWIV]
	Thamnovirus thamnaconi	Huángjiāovirus [HUJV]

 

Currently, the Filoviridae family includes nine genera of viruses found in Africa and Asia, of which only Ebola and Marburg viruses have been isolated from humans. RNA from various filoviruses has been detected in eight species of bats living in different regions of Africa, Asia, and Europe (Table 1) [3, 6, 8–10]. Furthermore, virus-specific antibodies have been detected in eight different species of bats [9–15]. At the same time, only one live filovirus isolate (Marburg virus associated with an outbreak of hemorrhagic fever among miners in Uganda in 2007) has been isolated from these animals [16]. In this regard, the question of the natural reservoir of filoviruses in nature requires further research.

Filoviruses in South and Southeast Asia

In Asia, the circulation of filoviruses was first described based on the detection of antibodies to Ebola virus nucleoproteins (NP) and glycoproteins (GP) in fruit bats (Rousettus amplexicaudatu) in the Philippines in 2010, while samples from five other bat species and ten bat species tested were negative [13]. Antibodies to the Reston virus and its RNA were also detected in fruit bats, pigs, and farm workers in Bangladesh [10]. In the People’s Republic of China (PRC), antibodies reacting with the Ebola virus antigen were detected in several species of bats in 2012 [17].

Studies on the detection of filoviruses in various species of bats, carried out using metagenomic sequencing or universal primers in the PRC, led to the description of previously unknown filoviruses that show significant divergence from known species and genera circulating in Africa. The identified viruses were fully sequenced and formed three new genera within the family Filoviridae: Dianlovirus, Striavirus, and Thamnovirus, whose prototypical representatives are the Mengla, Xilang, and Hungjia viruses, respectively (Table 2) [3].

 

Table 2. Time, place and source of isolation or detection of different filoviruses

Таблица 2. Год, место и источник выделения или обнаружения различных филовирусов

Genus Род	Virus Вирус	Year of detection Год выявления	Country of first isolation of pathogen Страна, в которой впервые был обнаружен возбудитель	Isolation source of pathogen Источник выделения возбудителя
Orthomarburgvirus	Marburg Марбург	1967	Germany Германия*	Human Человек
	Ravn	2007	Uganda Уганда
Orthoebolavirus	Zaire Эбола-Заир	1976	Zaire (DRC) Заир (ДР Конго)
	Эбола-Судан Sudan	1976	Sudan Судан
	Reston Эбола-Рестон	1989	USA США*	Monkeys Низшие приматы
	Tai Forest Леса Таи	1994	Uganda Уганда	Human Человек
	Bundibugyo Бундибяго	2007	Uganda Уганда
	Bombali Бомбали	2018	Sierra Leone Сьерра-Леоне	Bats Рукокрылые
Cuevavirus	Lloviu Ллови	2003	Spain Испания
Dianlovirus	Mengla Менгла	2015	China КНР
Striavirus	Xilang Ксиланг	2017
Thamnovirus	Huangjiao Хунгджиао	2017

Note. Ebolaviruses and Marburgviruses causing hemorrhagic fever in humans are highlighted in bold [18]; * – imported cases in regions where the pathogen is not endemic.

Примечание. Эболавирусы и марбургвирусы, вызывающие геморрагические лихорадки человека, выделены полужирным шрифтом [18]; * – завозные случаи в неэндемичных по возбудителю регионах.

 

Mengla virus: detection and molecular genetic characterization

The Mengla virus was detected during screening studies of organ samples (intestines, lungs, and brain) obtained from bats Rousettus leschenaultia (Chiroptera: Pteropodidae) caught in Yunnan Province, China, in 2013. The virus was detected by metagenomic analysis and using species-specific universal primers to conserved regions of the genome [19]. The partial genomic sequences obtained were similar to various genes of the Lloviu virus, Sudan virus, and Tai forest virus¹. Attempts to isolate the biologically active virus in Vero E6 cells were unsuccessful. As a result, the genome of the new virus was amplified and almost completely sequenced. The results of genetic analysis (32‒54% similarity when comparing complete genomes) allowed the Mengla virus to be isolated into a separate genus, named Dianlovirus, within the family Filoviridae. In dendrograms constructed on the basis of various proteins or complete genomes, the Mengla virus (genus Dianlovirus) forms a separate branch located between the viruses of the genera Orthomarburgvirus and Orthoebolavirus [18‒20].

The structure of the Mengla virus genome is characteristic of filoviruses. It has a negative-polarity RNA genome (ss(−)RNA) with the typical filovirus gene arrangement and composition: NP–VP35–VP40–GP–VP30–VP24–L. However, the Mengla virus has specific differences in the number of overlapping genes and a divergent sequence structure of the transcriptional terminal sequence. Unlike Ebola and Lloviu viruses, the GP gene of the Mengla virus encodes only one GP [18].

Despite the absence of a live isolate, it has been shown that the Mengla virus is replication-competent in minigenomic systems containing the leader and trailer sequences of Ebola and Marburg viruses [20]. The GP protein of the Mengla virus is capable of transducing human, primate, dog, hamster, and bat cells, indicating broad cellular tropism and the potential for interspecies transmission [21]. Like other filoviruses, the Mengla virus uses the Neumann‒Pick protein (NPC1) as a key receptor for cell entry [20, 22, 23].

Further monitoring studies of materials collected from various species of bats in 2009 and 2015 showed the widespread distribution of detected filoviruses in China (samples were collected at locations more than 200 km apart). In samples from bats of the Eonycteris spelaea and Rousettus sp. species, quantitative polymerase chain reaction (qPCR) was used to determine the tissue tropism of this group of filoviruses. Most often and in the highest titer, the Mengla virus and related viruses were detected in lung tissue samples. Viral RNA was also detected in blood samples (2 samples) and in other organs and tissues of animals. Meanwhile, the virus titer (based on PCR) in lungs was 1–3 orders of magnitude higher than in other organs (liver, kidneys, spleen, intestines, heart, blood). The results obtained indicate that the lungs are the preferred target organ for the Mengla virus (Table 3).

 

Table 3. The results of detection of RNA and filovirus antigens in bats of different species captured in Province Yunnan, China in 2009 and 2015 by different modifications of PCR, ELISA and immunoblot analysis [17, 21]

Таблица 3. Результаты выявления РНК и антигена филовирусов у различных видов рукокрылых, пойманных в провинции Юньнань, КНР в 2009 и 2015 гг. с помощью различных модификаций ПЦР, иммуноферментного анализа (ИФА) и иммуноблота [17, 21]

Time of detection (year, month) Год, месяц выявления	Place of bat capture Место отлова летучих мышей	Bat species Вид рукокрылых	Detection of filovirus RNA Выявление РНК филовирусов		Reveal of specific antibodies against Ebola virus (Freguency of reveal) Выявление специфических антител к вирусу Эбола (частота выявления в пробах)
			RT-qPCR ОТ-ПЦР-РВ	qPCR qПЦР	ELISA ИФА		Immunoblot Иммуноблот
					Zaire Заир	Reston Рестон	Zaire Заир	Reston Рестон
2009 Ноябрь November	Jinhong, Xishuanbanna County г. Джинхонг, округ Сишуаньбанна	Myotis ricketti	0/27		1/27
		Eonycteris spelaea and Rousettus sp.	10/43	5/43	6/43		2/43
2015 Декабрь December	Mengla County Округ Менгла	Asellis stoliczkanus	0/15
		Eonycteris spelaea and Rousettus sp.	5/42	10/42	14/25	7/25	11/25	4/25

Note. qPCR – quantitative polymerase chain reaction; RT-qPCR – real-time reverse transcription polymerase chain reaction.

Примечание. qПЦР – количественная полимеразная цепная реакция; ОТ-ПЦР-РВ – полимеразная цепная реакция с обратной транскрипцией в режиме реального времени.

 

Conclusion

Thus, data obtained in recent years indicate significant genetic diversity and widespread distribution of filoviruses among flying foxes (Chiroptera: Pteropodidae) in different regions of the world, including South and Southeast Asia. The discovery of new genera of the family Filoviridae, including Orthodianlovirus, highlights the necessity for further research into the biological properties and evolutionary relationships of these viruses. Although flying foxes and possibly some bat species are the natural reservoirs of filoviruses, this group of viruses has a high potential for interspecies transmission to other mammalian species, including humans. The Mengla virus demonstrates tropism and the ability to accumulate in the lung tissue of flying squirrels, which contributes to the emergence of variants capable of respiratory transmission. The species of flying foxes surveyed in China are frugivorous and may also potentially contribute to the contamination of fruit and lead to the infection of animals and humans that come into contact with them. In this regard, it is particularly important to monitor filoviruses in regions geographically close to the Russian Federation, taking into account the migratory activity of bats and the potential ability of new filoviruses to transmit between species to other mammals.

 

¹ Available at: http://wwwnc.cdc.gov/EID/article/21/9/15-0260-Techapp1.pdf

About the authors

Tatyana E. Sizikova

48 Central Scientific Research Institute of the Ministry of Defens of the Russian Federation

Author for correspondence.
Email: 48cnii@mil.ru
ORCID iD: 0000-0002-1817-0126

PhD, senior researcher

Russian Federation, 141306, Sergiev Posad

Vitaliy N. Lebedev

48 Central Scientific Research Institute of the Ministry of Defens of the Russian Federation

Email: 48cnii@mil.ru
ORCID iD: 0000-0002-6552-4599

DSc, professor, leading researcher

Russian Federation, 141306, Sergiev Posad

Sergey V. Borisevich

48 Central Scientific Research Institute of the Ministry of Defens of the Russian Federation

Email: 48cnii@mil.ru
ORCID iD: 0000-0002-6742-3919

DSc, professor, academician of RAS, head of the institute

Russian Federation, 141306, Sergiev Posad

References

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