An insight in to Zoonotic and Reverse Zoonotic Potential of Rotavirus
Basanti Brar1, Sumnil Marwaha2; Prasad Minakshi3*
1HABITAT, GIPPCL, Biofertilizer Production and Technology Centre, CCS Haryana Agricultural University, Hisar, Haryana, India; 2ICAR- National Research Centre on Camel, Bikaner; 3*Department of Animal Biotechnology, Lala Lajpat Rai University of Veterinary and Animal Sciences, Hisar, India
Corresponding authors email: minakshi.abt@gmail.com
Abstract
One of the biggest challenges to securing the “One Health” idea in the current environment is the emergence of viral zoonotic illnesses. Furthermore, because the majority of viral zoonoses are transmitted by wildlife, it is challenging to anticipate future outbreaks due to inadequate understanding of the global virome database. A number of new viruses that need to be reported, including the influenza, Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), Ebola, Hendra, Nipah, and Zika viruses, are now the main contributors to epidemics and the associated human and animal mortality. The most common symptom of gesteroentritis in both people and animals is caused by rotaviruses, which are non-enveloped RNA viruses that are members of the Reoviridae family. Rotaviruses have an 11-segmented double-stranded RNA (dsRNA) genome that is surrounded by a complex architecture. Rotavirus infection is the main viral cause of calf diarrhoea, an important multi-pathogen-mediated (including viruses, bacteria, and protozoa) gastrointestinal disease of veterinary importance that causes large financial losses to the dairy sector globally. Significant concerns for rotavirus epidemiology result from rotaviruses’ capacity for zooanthroponotic and anthropozoonotic transmission. According to findings up to this point, humans can become infected with rotaviruses from animals only by direct transmission or through gene reassortment between rotaviruses from animals and humans. The current article focuses on the structure, diversity, and significance of rotavirus in zoonotic and reverse zoonotic transmission.
Introduction
Emerging viral zoonotic diseases are one of the major obstacles to secure ‘One Health” concept under current scenario. Moreover most of the viral zoonoses originate from the wildlife and poor knowledge about the global virome database renders it difficult to predict the future outbreaks. Several notifiable emerging viruses like influenza, Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), Ebola, Hendra, Nipah and Zika viruses have become the leading causes of epidemics and losses thereto in both human and animals. The sufferings are higher due to gastroenteritis causing viruses including Astrovirus, Calicivirus, Enterovirus, Kobuvirus Picobirnavirus, Sapelovirus, Teschovirus, and many more. Notably, the majority of the emerging viruses enclose RNA genome and these are more prone for insertions/mutation in their genome, leading to evolving viral variants. Rapidity in viral evolution becomes a big hitch in the development process of successful vaccines or antiviral. The prominent gastroenteric virus is rotavirus, which is a double-stranded RNA virus with a segmented nature of genome enabling higher reassortment events and generates unusual strains with unique genomic constellations derivative of parental rotavirus strains. Although most rotaviruses appear to be host restricted, the interspecies transmission of rotaviruses has been well documented across the globe. Rotaviral diarrhea is an early extinguisher of blooming lives in several animal species as well as humans. Although it is distributed worldwide, countries of Sub-Saharan Africa, South, and South-East Asia are the worst affected. The approximate accountability of global children mortality due to rotaviral diarrhea figures around 215,000 annually. Various large and small ruminants are also extremely susceptible and the mortality usually stands nearly 5 to 20% in neonatal calves which can climb up drastically due to poor management and unhygienic condition. The nocturnal bats have been accepted harbouring many pathogenic viruses and servingas natural reservoirs. Indications are that bats can also harbour rotaviruses, and help in virus spread. The zooanthroponotic and anthropozoonotic potential of rotaviruses has significant implications for rotavirus epidemiology. Hitherto reports confirm infection of humans through rotaviruses of animal origin, exclusively via direct transmission or through gene reassortments between animal and human strain of rotaviruses. The current article is focused on rotavirus structure, diversity as well as zoonotic and reverse zoonotic importance of rotavirus.
Rotavirus genome organization and structure
Rotaviruses are non-enveloped RNA viruses. These viruses basically belong to the Reoviridae family and have 11 segmented, double-stranded RNA (dsRNA) genome which is surrounded by a complex architecture of three concentric capsids i.e. inner core layer, middle layer and outer capsid layer. The electrophoretic migration pattern of RNA of many bovine rotaviruses is 4:2:3:2 which is the characteristic of RVA. The 11 segments of RNA genome encodes 6 structural proteins denoted as “VP” [ VP1, VP2,VP3, VP4, VP6 & VP7] and 6 non-structural proteins denoted as “NSP” [NSP1, NSP2, NSP3,NSP4, NSP5 & NSP6] . The 11th segment of the viral genome synthesizes 2 proteins i.e. NSP5 & NSP6. The VP4 & VP7 proteins form the outer capsid layer of virus and both proteins play a role to induce neutralizing antibodies. The inner capsid or middle layer in icosahedral symmetry and consists of VP6 protein. The innermost core layer is formed of VP2 proteins and on inner side of this layer VP1 and VP3 proteins are attached. Inside the inner capsid layer there is virion core which made up of VP1, VP3 & dsRNA genome of virus. Rotaviruses are unique and in comparison to most cellular mRNAs, rotavirus mRNAs lack poly A tail but have a 5′-terminal cap. During replication, the viral mRNAs either can directly synthesize dsRNA or firstly synthesize (-) strand of RNA then dsRNA synthesis takes place
Rotavirus Classification
On the basis of genetic variability and serological reactivity of group-specific antigen VP6, rotaviruses are divided into 8 groups, classified as RVA-RVH (Rotavirus A, Rotavirus B-H, etc.) and after that, RVs recocgnised in sheltered dogs and bats as new species (RVI and RVJ) in Hungary and Serbia are reported, however confirmation is pending. The first three groups, RVA, RVB and RVC, are more prevalent pathogens present in humans and different animal species. While, RVE has been analysed only in pigs and RVD, RVF and RVG are utterly observed in birds. Till now, a plethora of rotavirus group have been reported in avian and mammalian hosts such as human, cattle, sheep, pigs, goats, rat, chicken and turkey, dogs, juvenile ferrets, cats, horses, non-human primates, antelope, bat, guanaco, vicuna, mouse, rabbit, giant panda, camelids to name a few. High diversity has been noted in RVA than other RVs.
According to RCWG (Rotavirus Classification Working Group) 36G & 51P types of RVA are identified in different species like out of these genotypes of RVA G1-G4 genotypes are of human origin while G6, G8 G10 genotypes specifically are of bovine origin. And in bovines P1, P5 and P11 are identified and in humans P4, P6 & P8 are reported. This classification system helps to elucidate the evolutionary mechanism of new strain emergence and potential origin of new strains.
Zoonotic and reverse zoonotic transmission of Rotavirus
Calf diarrhea is a vital multi-pathogen-mediated (include viruses, bacteria, and protozoa) enteric disease of Veterinary importance inflicting significant economic losses to the dairy industry worldwide, and Rotavirus infection is a predominant viral impetus underpinning this misery. Calf diarrhea has inflicted 57% of the weaning calf mortality, particularly in below one-month-old calves as reported by The 2007 National Animal Health Monitoring System (NAHMS) for U.S. dairy while around 53.4% of calf mortality has been evidenced in Korea from the disease. The estimated average annual economic loss from calf mortality due to rotavirus diarrhea has accounted for around $3-8 million from 1970 to 1976. Whereas it coasted at around $10 million per year in Norway in 2006. Recently, about 32-38% of samples of Neonatal calf diarrhea (NCD) from organized cattle farms in China has been reported to be positive for Rotavirus and a high incidence of co-infection with multiple pathogens has also been observed. Further, the calves born in crowded herds or maintained in larger groups received insufficient colostrum and weaned at a younger age are more prone to rotavirus infection. Lamas, primates, wild animals of the Bovidae family, wild rabbits, and wild birds like pheasants serve as the wild hosts of the virus.
The veterinary importance of rotavirus infection is not only restricted to the economic burden imposed on the livestock farming system due to treatment cost, production loss from the morbidity and mortality of the animals but also the zoonotic and reverse-zoonotic potential of the pathogen. The extremely broad host-specificity of the virus, ranging from humans to domestic animals and birds as well as the susceptible wild hosts may easily facilitate the zoonotic and reverse-zoonotic transmission of the pathogen to challenge the sanctuary of ‘one health’ notion. The fecal-oral route has been depicted as the predominant mode of transmission of the virus. It was discerned that one gram of rotavirus infected stool contains more than 1011 virions. High viral loads have also been reported in young infected animals such as piglets. Rotavirus particles may persist for several days in the environmental condition which also facilitates their transmission. Further, transmission through the respiratory route as air-borne infection and water-borne transmission of the virus has also been reported. Zoonotic transmission can take place as food-borne infection through ingestion of meat from diseased animals, crops exposed to contaminated farm-wastes, or foods contaminated by the handling of farmworkers exposed to infected animals. Generally, rotaviruses are species-specific but it has been demonstrated experimentally that interspecies transmission is possible and comparison between genomic sequences of animal & human rotaviruses revealed their close identity. In human population many uncommon genotypes have been reported which are so similar to domestic animal rotaviruses. There is potential threat for zoonotic transmission between human and domestic animals and vice-versa. In rural areas and in farming communities chances of such transmission are more because in such places animals and humans are in very close contact. Although, there will be no high level infection by this exposure but some animal viral infection to be continued in humans.
One species to specific has been reported that rotaviruses are posing a higher risk to another species by the emerging as a more pathogenic reassortant rotavirus strain. It has been identified that novel strain of rotavirus which is evolved by interspecies transmission and natural reassortment of their genome between buffalo and feline or caprine viruses and intraspecies transmission of virus in host also results in the natural reassortment of genomic segments and leads to emergence of new genotypic combination or strain. Serious threat of zoonotic transmission of G10 genotype of bovine rotavirus from buffalo to human and vice-versa has been reported.
Human rotaviruses has been reportrted and has shown potential threat to zoo anthroponotic transmission to ovine species in Haryana state of northern India. The interspecies transmission was confirmed between artiodactyl and human in Morocco. Evidences of human to animal transmission of unusual genotypes G10P[33], G6P[14] of BRV has been reported in western India. Their phylogenetic studies have confirmed the sequences of these different species viruses are closely clustered. So, inter as well as intra-species transmission of rotavirus takes place which further causes their genomic segment exchange and evolve as a new virus strain in host species.
CONCLUSION
Efficient control of emerging and re-emerging viral zoonotic diseases require ample alertness and critical strategic inputs which is beyond the scope without prior knowledge about the global virome database and their zoonotic potential that can aid in prediction of the upcoming outbreaks. After the first occurance of RV in humans during 1970s, the wide list of host species showing RVs in different species has identified. The RV infection has been reported in a broad range of species. The trend for reporting pathogen spread of human-to-animal and human transmission to animal is increasing. This paper was designed to summarize the zonotic and reverse zoonotic transmission of rotavirus. Prospective research should also contain a wider kinds of etiological agents and animal species and the detection and transmission of human diseases in animals to exemplify the richness of literature on this aspect will be recogised and accessible through myriads of disciplines. A wider knowledge and understanding of zoonosis and reverse zoonoses should be essential for a successful One Health response. We recommend that future literature is also required on how human disease can, and does, affect the animals around us.
