Le Infezioni in Medicina, n. 2, 117-127, 2019 REVIEW 117

Nipah virus The rising epidemic: a review

Rohan Kumar Ochani, Simran Batra, Asim Shaikh, Ameema Asad MBBS, Department of Internal Medicine, Dow University of Health Sciences, Karachi, Pakistan

SUMMARY The was discovered twenty years ago, and sub-continent, Indonesia, Southeast Asia, Pakistan, there is considerable information available regarding southern China, northern Australia and the Philippines, the specificities surrounding this virus such as trans- as demonstrated by the multiple outbreaks in 2001, mission, pathogenesis and genome. Belonging to the 2004, 2007, 2012 in Bangladesh, India and Pakistan as genus, this virus can cause , enceph- well as the initial outbreaks in and Singapore. alitis and respiratory disorders. The first cases were re- Multiple routes of the viremic spread in the human ported in Malaysia and Singapore in 1998, when affect- body have been identified such as the central nervous ed individuals presented with severe febrile encepha- system (CNS) and respiratory system, while virus lev- litis. Since then, much has been identified about this els in the body remain low, detection in the cerebro- virus. These single-stranded RNA viruses gain entry spinal fluid is comparatively high. The virus follows into target cells via a process known as macropinocyto- an incubation period of 4 days to 2 weeks which is fol- sis. The viral genome is released into the cell cytoplasm lowed by the development of symptoms. The primary via a cascade of processes that involves conformational clinical signs include fever, headache, vomiting and changes in G and F proteins which allow for attach- dizziness, while the characteristic symptoms consist ment of the viral membrane to the cell membrane. In of segmental myoclonus, tachycardia, areflexia, hypo- addition to this, the natural reservoirs of this virus tonia, abnormal pupillary reflexes and hypertension. have been identified to be fruit bats from the genus The serum neutralization test (SNT) is the gold stand- Pteropus. Five of the 14 species of bats in Malaysia have ard of diagnosis followed by ELISA if SNT cannot be been identified as carriers, and this virus affects horses, carried out. On the other hand, treatment is supportive cats, dogs, pigs and humans. Various mechanisms of since there a lack of effective pharmacological thera- transmission have been proposed such as contamina- py and only one equine vaccine is currently licensed tion of date palm saps by bat feces and saliva, noso- for use. Prevention of outbreaks seems to be a more comial and human-to-human transmissions. Physical viable approach until specific therapeutic strategies are contact was identified as the strongest risk factor for devised. developing an infection in the 2004 Faridpur outbreak. Geographically, the virus seems to favor the Indian Keywords: Nipah virus, outbreaks, vaccine.

n INTRODUCTION nucleotides long, which accounts for them to be 15% longer than others in their family. Moreo- iscovered two decades ago as aetiolog- ver, the genetic characteristics found in the genus Dic agent of a zoonotic disease, Nipah virus Henipavirus, include the unique, 3’ leader and 5’ (NiV), is a member of genus Henipavirus in the trailer sequences, which promote transcription Paramyxoviridae family. Unlike the Hendra Vi- and replication of genomic RNA, respectively [1]. rus, which is 18234 nucleotides long, NiV is 18246 Categorized as Category C priority pathogen by the Centers for Disease Control and Prevention (CDC) and the National Institute of Allergy and Corresponding author Infectious Diseases (NIAID), its clinical manifes- Rohan Kumar Ochani tations include fever, , and in severe E-mail: [email protected] conditions, respiratory and pulmonary disorders 118 R.K. Ochani, S. Batra, A. Shaikh, A. Asad

affecting numerous systems of the body [2]. Af- The virus particles are pleomorphic in shape, al- ter its discovery from Sungai Nipah (Nipah River tering from spherical to filamentous, and have a Village), where its name originally came from, the diameter of approximately between 40 and 600 first cases characterized by severe febrile enceph- nm [6]. NiV is covered with a lipid capsule encom- alitis in humans were reported in Singapore and passing a nucleocapsid. A single layer of surface Malaysia, between 1998 and 1999 [3]. projections surrounds NiV envelope, showing the Transmission of NiV has been reported by vari- attachment and fusion proteins. The nucleocapsid ous ways which include human-to-human trans- core comprises of the genomic RNA, nucleocapsid mission and food-borne transmission [2]. The protein, polymerase, and phosphoprotein, while natural reservoir of the virus are bats of genus the envelope comprises of the matrix protein Pteropus; therefore, proximity with bats is one of which preserves the virion structure. Although the reasons for the occurrence of NiV and swal- members of the paramyxovirus family typically lowing of raw date palm sap is another [1]. Fur- have a genomic length of 15,500 nt, the HeV has a thermore, the virus spread in Singapore due to length of 18,234 nt. [7]. handling and holocaust of pigs [4, 5]. The mortal- Entry of the NiV in the target cells is typically ity rate was approximately 40% in Malaysia and through a process of macropinocytosis via the Singapore, compared to 70% in India and Bang- glycoprotein and fusion protein. The two cellular ladesh, where the outbreaks of NiV are frequent. receptors bound in the process are ephrin-b2 and Considering its degree of endemic in South Asia, ephrin-b3, which leads to a conformational change systemic surveillance is required to overcome its of the G and F proteins. Following the receptor recurrence and rising mortality rates [2, 3]. binding F fusion activity is assisted by the glyco- protein via an unknown mechanism, resulting in a conformational change leading to the entry of fu- n METHODS sion peptide into the host cell. Afterwards, the viral Systematic literature review membrane attaches to the cellular plasma mem- For this review, a literature search was conduct- brane leading to the delivery of the core and the ed using PubMed and Google Scholar from their release of the viral genome to the cytoplasm, but inception to November 2018. The search string in- before the entry, the M protein shell and N protein cluded the following keywords: (“Nipah virus”) need to be disrupted due to an unknown mecha- AND (“outbreak” OR “transmission” OR “clinical nism. Moreover, the pathway to transcription and manifestation” OR “neurologic manifestation” OR replication of the Nipah virus is presumed to be “geographic distribution” OR “global distribution” similar to those of other paramyxoviruses. The ba- OR “genomic distribution” OR “etiology” OR “cau- sic functional component needed for the replica- sality” OR “genomic structure” OR “pathogenesis” tion and transcription is the combination of tightly OR “treatment” OR “prevention” OR “control” OR bound negative sense RNA with N proteins and “biosafety” OR “economic burden”). Articles in oth- RNA polymerase complex. The primary transcrip- er than the English language were excluded. tion consists of the RNA polymerase complex to be packaged inside the virion, which copies the viri- NiV genome, structure and replication on RNA (vRNA) and then generates, capped, short Like all other paramyxoviruses, NiV and HeV are uncapped RNAs and polyadenylated mRNAs, en- also single-stranded RNA viruses which replicate coding viral proteins [8, 9]. in the cytoplasm; however, NiV is 12 nucleotides longer than HeV and therefore have the largest Vectors, transmission and reservoirs genome in their family. Right after its emergence The first cases of Nipah virus were recognized in in 1999, Harcourt et al. described the genomic re- pigs showing symptoms of respiratory disease lationship between other paramyxoviruses and and in a few cases, neurological deficits, in 1998 in NiV. The authors also studied to identify the vari- Malaysia. Most pigs had asymptomatic infections ous genes involved in the genomic making of the and a majority of them fully recovered. Exposure virus, which included the nucleocapsid (N), phos- to ill pigs resulted in transmission to humans phoprotein (P), matrix (M), fusion (F), and glyco- where 276 individuals developed encephalitis. protein (G) genes [6]. Unlike other Paramyxoviruses, the Nipah virus Nipah virus - the rising epidemic: a review 119

demonstrates a wide host range, infecting mul- pigs being euthanized, leading to a steep decline tiple species of animals such as horses, cats, and in international trade of the region. However, the dogs, as well as humans. The natural reservoirs for infection did not remain cornered in Malaysia, and the virus are fruit bats from the genus Pteropus. 5 the diseased transmission accelerated when the of 14 bat species in Malaysia have been identified virus afflicted pigs moved 160 miles in the state of as carriers of the virus with Pteropus hypomelanus Negri Sembilan. These pigs from Negri Sembilan and Pteropus vampyrus having the highest rates were kept and slaughtered in an abattoir in Singa- of seroprevalence with the infectious virus being pore, and the virus subsequently spread to the ab- identified in their urine and saliva.Pteropus hypo- attoir workers. An alarming mortality rate of 40% melanus and Pteropus lylei were isolated as being was noted and the majority of patients presented carriers in South and South East Asia. All four with a severe acute encephalitis syndrome and a species of this genus located in Austria were also proportion of patients presented with pulmonary identified as being carriers. When bats from this findings. However, to one’s surprise, no new cas- genus are inoculated with Nipah virus, it results es have been reported from either Malaysia or in active infection without clinical disease symp- Singapore since 1999 [5, 11]. toms solidifying their role as reservoirs. There is Nevertheless, from 2001 continuing cases of NiV some evidence to suggest that female bats, in the have been reported from Bangladesh and the vi- states of pregnancy and lactation, are more sus- rus has regrettably disseminated to affect regions ceptible to infection. of India. The first outbreak in Bangladesh was re- Transmission of the virus takes place horizontal- ported in 2001, from followed ly via urine, feces, and saliva. The highest risk of by uninterrupted outbreaks in selected regions infection in bats, however, occurs when there is every year. Moreover, sporadic cases of NiV en- nutritional stress due to climate change and habi- cephalitis have been reported, up to March 31, tat loss which alters food sources. There is no ev- 2012, a total of 209 NiV human cases were report- idence to suggest that direct bat to human trans- ed and constituted a mortality rate of 77%. Addi- mission takes place; instead, the virus spreads tionally, two outbreaks of NiV encephalitis in the via body fluids [8]. In the Bangladesh outbreaks eastern state of West Bengal in India, bordering ranging from 2001 to 2008, the transmission meth- Bangladesh have been reported in 2001 and 2007. ods were identified as contamination of date palm The mortality rate observed in India was estimat- saps by bat feces and saliva, nosocomial transmis- ed to be 70%. In 2001, the outbreak was observed sion, and human to human transmission. The case in Siliguri, West Bengal and the clinical material for the human to human transmission was made obtained confirmed Nipah virus-specific immu- by the 2004 Faridpur outbreak where physical noglobulin M (IgM) and IgG antibodies in 9 out contact was identified as the strongest risk factor of 18 patients. The second outbreak in 2007 was for developing an infection. Physical contact with in Nadia district of West Bengal. According to the a single ill individual resulted in transmission surveillance and outbreak reports by the World through 5 generations, 34 individuals in total [10]. Health Organization (WHO) assessing NiV out- breaks in South-East Asia from 2001-2012, the av- Geographic distribution erage case fatality rate is 74.5% [8]. However, in During an outbreak of encephalitis in September the relation of NiV transmission, contrary to the 1998 in pig farms of Ipoh in Peninsular Malaysia, Malaysia-Singapore 1998 outbreak being consist- which was initially presumed to be due to Japa- ent by a porcine epidemic transforming over time nese encephalitis, the suspected cases isolated to a human epidemic, the outbreak in Bangladesh were 265, and the virus occupied the region till has portrayed an on-going NiV transmission from April 1999 [5, 8]. It initially afflicted pig handlers, bats to human [10]. and a team of multidisciplinary investigators em- Deka M.A. and Morshed N. have outlined the dis- ployed clinical and autopsied findings from 32 ease transmission in South and South East Asia fatal human cases of NiV infection; electron and and coherently linked it to factors predisposing light microscopy confirmed the viral inclusions of this region for repeated outbreaks of NiV. The NiV. This first outbreak led to a significant eco- analysis demonstrated a favorable environment nomic loss to Malaysia owing to over a million in vast areas of the Indian sub-continent, Indo- 120 R.K. Ochani, S. Batra, A. Shaikh, A. Asad

Figure 1 - Number of reported cases and deaths by year due to previous NiV outbreaks.

nesia, Southeast Asia, Pakistan, southern China, and northwestern districts or the “Nipah Belt”, northern Australia, and the Philippines. In Bang- a district in Bangladesh which is significant con- ladesh, NiV causes high mortality rates with the cerning repeated outbreaks of NiV since 2001 [12]. majority of human cases occurring in the central Until recently, first NiV outbreak cropped up in

Figure 2 - Global distribution of NiV. Nipah virus - the rising epidemic: a review 121

Kerala State of India, and the third outbreak in In- the dendritic cells confine the virus, get infected dia after the surge of NiV in 2001 and 2007. Recent- and then pass on the virus to circulating leuko- ly in May 2018, state had a total of 23 NiV cytes. These leukocytes then, without themselves cases (18 confirmed and 5 probable), out of which, being infected, could trans-infect the virus to 16 out of 18 confirmed cases ultimately died. The endothelial vascular cells. As per the literature, outbreak was localized to two districts in Kerala CD169 on human dendritic cells was suggested to State: Kozhikode and Malappuram. However, execute the trans-infection pathway used by the no new cases or deaths have been reported after virus. The second mode of transmission shows this [13]. Finally, sequencing of different NiV iso- the direct entry of the virus into the CNS via ol- lates revealed that the NiV strains isolated from factory nerves. Even though, this pathway does different hosts in Malaysia were very similar at correlate with a direct entry into the CNS through the genome sequence level, on the contrary, the oropharyngeal innervations, spread within the NiV strains from Bangladesh and India exhibited brain remains questioned [14]. a greater genetic diversity. The NiV outbreaks and Further possible ways include by the endocytic the number of cases in different years have been mechanism of macropinocytosis, but this meth- shown in Figure 1 and Figure 2. od needs further investigations. Other than that, low-level replication in human dendritic cells Pathogenesis shows that it can spread through adjunct with NiV upon entering the human body spreads monocytes and lymphocytes and via cell-free through various routes, which include the central viremia. Epithelial cells can also be a route for nervous system (CNS) and respiratory system. the transmission of infection either from the basal The viremic spread of the infection involves en- membrane or by fusion with neighboring epithe- dothelial cells, epithelial cells, and dendritic cells, lial cells. This route indicates the possible spread while the significant NiV receptors in the human of the virus to the lungs other than through the body have been found out to be Ephrin B2 and airway route. Ephrin B3 [14]. In conclusion, no vascular involvement is found Despite the low levels of virus detected in humans, in late-onset encephalitis with neuronal cells be- the viremic spread is the critical path of diffusion ing the target cells. Neurological relapse can oc- in CNS, and segregation of the virus from the cer- cur in some infected individuals if Henipavirus ebrospinal flood can be achieved. The emblem of perseverates in the CNS. The means of spread Henipavirus infection is damage of the endothelial from the previously infected mucosal tissue to the cells of the small blood vessels, which leads to the endothelium of various targeted organs and the advancement of the virus into various organs and CNS remains to be determined. Even though the through the blood-brain barrier and blood-air bar- virus is found in all organs, brain microvascular rier, which lead to the spread of the infection in the vessels are the most commonly targeted. Further brain and lungs [15]. As indicated by clinical and advancement in the understanding of the virus autopsy studies, endothelial cell damage is the pri- is needed for the determination of antiviral treat- mary reason of Henipavirus infections which leads ment [14, 15]. to systemic vasculitis of small blood vessels, necro- sis and extensive thrombosis [16]. Association with Clinical manifestations shedding and human-to-human transmission with Although there is a slight difference in the genom- the Ni-B genotype may be responsible for more ic structure of NiV and HeV, the clinical manifes- critical respiratory forms of the infection. Interest- tation of these diseases is very much similar. The ingly, unlike pig monocytes, which were shown clinical symptoms of NiV can lead to grave con- to be successfully infected by the virus, human sequences due to its rapid phase of encephalitis, monocytes did bind to the virus but showed no which leads to a high mortality rate. signs of a thriving infection [14, 15]. Initially, there is an incubation period of 4 days Two models have been proposed to show the dis- to 2 weeks, after which the symptoms start to de- semination of the virus within the host. The first velop. The primary clinical signs, characteristic model indicates the association between NiV and symptoms and severe symptoms are shown in circulating cells of the body which suggest that Table 1 [3, 17]. 122 R.K. Ochani, S. Batra, A. Shaikh, A. Asad

In a randomized controlled trial conducted by mortalities (73%) in outbreaks seen in Bangla- Goh et al. among pig farmers in Malaysia showed desh, compared to Malaysia (32%), partly due to that almost all patients (n=91/94, 97%) had com- better healthcare facilities in Malaysia and partly plaints of fever while 65% experienced headaches. due to emerging strains of NiV in further out- It also showed that more than half of the patients breaks in Bangladesh, after its original occurrence experienced an altered level of consciousness and in Malaysia in 1999. involvement of the brain system, suggesting that its involvement can lead to death due to post-ef- Diagnosis fects of encephalitis [18]. Patients with a reduced The virus was isolated from cultured mammali- level of consciousness had and visible an tissues after its first outbreak in 1998, which cerebellar signs along with tachycardia. There subsequently highlighted the idea of a new infec- was also a dramatic, continuous, segmental myo- tious etiology. Since then, NiV is internationally clonus seen in 56% of the patients with a reduced recognized as a dangerous zoonotic pathogen for level of consciousness, which was much higher which there is currently no available vaccine or than the further outbreaks occurring in parts of effective treatment. Hence, it imposes the highest Bangladesh [19]. level of bio-risk management, which is adequate- Furthermore, due to the involvement of the brain- ly combatted by using containment approaches stem, these patients showed essential signs of commonly designated as bio-security level (BSL) pinpoint pupils with variable reactivity, abnormal 4 or physical containment (PC) 4 [20]. doll’s-eye reflex, noticeable vasomotor changes The laboratory diagnosis of NiV infections in- comprising of hypertension and tachycardia sug- cludes a wide array of methods. Conventional gesting a presence of involvement of the medul- polymerase chain reaction (PCR) has been widely lary vasomotor part of the brain-stem. Dizziness used in the past for the detection of viral isolates and vomiting were seen in about one-third of the in human and animal reservoirs. However, with patients, while a nonproductive cough and myal- advancements in rapid detection methods, tests gia was seen in 14% and 12% patients, respective- based on conventional PCR are now considered ly. Although, patients who experienced late-on- substandard and no longer in use for diagnostic set or relapse encephalitis had a lower mortality purposes. In 2004, a specific TaqMan Real-Time (18%) than the ones with acute NiV encephalitis PCR (RT-PCR) of the Nipah nucleoprotein was (40%), but the ones with late-onset or relapse developed to characterize field specimens or lab- experienced higher/worse neurological deficits oratory material rapidly. This technique proved (61%) than the ones who had acute encephalitis to be sensitive and reliable for rapid detection of (22%) [18]. Therefore, further investigations and NiV RNA for diagnosis [21]. studies need to be conducted to assess the factors Furthermore, Sanger sequencing also played a related to relapsing of encephalitis to help reduce pivotal role to provide insight into NiV clinical mortalities due to severe neurological deficits. and structural correlates. Sequencing of different Generally, high mortality (40-70%) is seen in pa- NiV isolates revealed NiV strains and, current- tients with NiV. There was a higher number of ly, viral isolation is the primary means of virus

Table 1 - Clinical due to Nipah virus infection. Primary clinical signs Fever Headache Vomiting Dizziness Characteristic Segmental Hypertension and Hypotonia and Abnormal pupillary symptoms myoclonus tachycardia areflexia reflexes Severe symptoms Pulmonary syndrome Neurological signs Cough Confusion Diffuse alveolar shadowing and acute Motor deficits and reduced level respiratory distress syndrome (ARDS) of consciousness Hypoxemia Seizures Abnormal X-ray chest findings Abnormal MRI findings Nipah virus - the rising epidemic: a review 123

detection for the confirmation of any new NiV During the 2018 outbreak of NiV in Kerala, the outbreak. Once the virus has been isolated, the first line of testing for the diagnostic purpose subsequent identification of virus isolates can was employed as RT-PCR or NiV RNA detection. be sought by immunostaining of fixed, infected While the second line testing for research purpose cells, neutralization with specific antisera, PCR involved detection of anti-NiV IgG and IgM and of culture supernatants, and electron microsco- was carried out by the CDC. Later in the year, py. Nevertheless, it demonstrates limited sensi- the University of Manipal in India along with a tivity which possibly can be encountered by an company Molbio introduced Truenat Test Chips adequate quantity of samples. Serological test- by Point of Care Real-Time micro-PCR for NiV di- ing has been used in the past by surveillance and agnosis [26]. According to the (CDC) guidelines, control programs after outbreaks for infected an- a patient with a clinical history of NiV can be di- imals and premises, particularly for NiV infec- agnosed during the acute phase by virus isolation tions in pigs in Malaysia. As a part of serological techniques and real-time polymerase chain reac- testing, serum neutralization test (SNT) is still tion (RT-PCR) from the throat and nasal swabs, regarded as a gold standard; however, it requires cerebrospinal fluid, urine, and blood while anti- PC4 facilities in the laboratory owing to the BSL4 body detection by ELISA (IgG and IgM) can be risk of NiV. used later on [27]. On the contrary, in schematic situations where the PC4 facility is unavailable, ELISA is designated Treatment and prevention as the most affordable and straightforward meth- Treatment of individuals infected with the NiV is od. It is favorable in epidemiological studies and currently limited to supportive care. Due to phys- on-going surveillance programs. However, unfor- ical human to human contact being the highest tunately, it is reiterated that the ELISA does not risk factor for transmission of infection, extra cau- have 100 percent specificity. False positives can tion is demonstrated during the management of lead to a potential economic loss for pig farmers these patients. There are no licensed therapeutic while false negatives can aggravate the public interventions for treating the NiV. While antiviral health, thus remain as a mainstay of concern [20, treatment seems to be the obvious choice, current 22]. Until recently in 2012, a serum neutralizing intervention strategies are remarkably few. test was developed which measured NiV neutral- Two drugs have been identified, namely: riba- izing antibodies under BSL2 risk management. virin and chloroquine however, any therapeutic This method produced higher neutralizing an- effect they have has not been definitively estab- tibody titer in comparison to conventional SNT lished. However, in the case of , in vit- and required almost 10-fold less serum [23]. ro studies have demonstrated it to be effective Furthermore, since NiV grows in cultured cells against NiV replication. The use of ribavirin was to high titers, it is visualized in the medium of also seen in a male survivor, from the latest Ker- infected cells by negative contrast electron mi- ala Nipah outbreak, with the absence of any res- croscopy, and it remains as the first method for piratory disorder. Eventually, on day 16 and 26 identification of a new causative agent in disease post onset of illness, the presence of NiV RNA outbreaks [20, 24]. was seen to be in the male survivor’s semen, In 2012, samples were taken in Bangladesh from however, the conclusion whether the virus was suspected cases and were confirmed as positive viable in semen or it can be transmitted through if IgM against NiV was found in samples, if NiV sexual routes could not be drawn [12, 28]. Multi- RNA was amplified or if NiV was isolated from ple trials employing Ribavirin have been carried samples. Then the genomic sequences from two out, but their results have been contradictory. patients in 2008 and partial genomic sequences While it reduced mortality by 36% in an older from three patients in 2010 were characterized study, recent animal studies suggest that it does and compared with distinct genomic sequences not have any clinical benefit [29]. Conversely, the from patients in Faridpur and Gopalganj district. anti-malarial drug chloroquine, was shown to This led to a standardized genotyping protocol inhibit NiV in cell cultures; however, it was also for NiV with an accurate way to classify current shown not to have any clinical benefits in recent and future NiV sequences [25]. animal models. 124 R.K. Ochani, S. Batra, A. Shaikh, A. Asad

On the other hand, passive immunotherapy with a The first area for targeted intervention is food- monoclonal antibody which is specific for viral en- borne transmission; preventive measures against velope glycoproteins (NiV G-protein) has offered this include washing and peeling of fruits before some success. The human monoclonal antibody consumption and discarding ones with visible (mAb) called m102.4, isolated from a recombinant signs of bites or tampering [33]. Furthermore, nae human phage-displayed Fab library has dis- Bangladeshi villagers need to be discouraged played some promise and might be approved for from consuming fresh raw date palm sap due to future use. It has been proven to possess potent probable contamination with NiV. The general neutralization activity against the NiV and has population should be encouraged to cook fluids demonstrated effective post-exposure therapy in at temperatures above optimum levels to ensure ferrets and primates (nonhuman). When adminis- virus destruction. Methods also need to be de- tered 10, 24 or 72 hours after exposure to the virus; vised to prevent bats from accessing date palm it resulted in protection against a 10-fold lethal trees in regions where sap is consumed raw. Even virus challenge, intratracheally and oral-nasally though these methods are still being assessed for [30]. In ten instances, individuals exposed to the potency and reliability, they may help to prevent virus were given m102.4 and did not develop the the spread of NiV in Bangladesh [10]. virus. Therefore, it is essential to recognize that Finally, the most widely used preventative meas- m102.4 has proven to be useful for pre and post ures to reduce the spread of the virus via ani- exposure prophylaxis before the development of mal-to-human transmission include restraining clinical symptoms in animal models. However, the movement of animals from infected farms to once disease onset takes place, it loses its reliability. other areas and covering hands with gloves dur- Additionally, very recently, the nucleoside analog ing the process of annihilation. Proper cleaning

4’-azidocytidine (4’N3-C, R1479) and it 2’-mono- of infected farms with correct detergents is also fluoro (2’F-4’N3-C), and 2’-difluoro (2’diF-4’N3-C) necessary to prevent the infection from spreading analogs have demonstrated enhanced antiviral [33]. In low socioeconomic countries like Bangla- activity against paramyxoviruses including the desh, where the total amount spent on health ser- NiV. To make sure their action was due to non-cy- vices per person per year is as low as $ 12, family totoxic effects, they were tested on NCI-H358 cells members provide the most direct health care, even for three and seven days. Minimal toxicity was ob- in hospital settings. In such conditions, it should served. The 2’ monofluoro analog proved to be the be the responsibility of healthcare staff to ensure most potent against the NiV, even in human pri- that family members of infected individuals real- mary small airway cells [31]. Furthermore, anoth- ize the importance of handling infected saliva to er drug of Japanese origin, , another nu- prevent human-to-human transmission of the in- cleoside analog, has shown great promise. In vitro, fection. Moreover, caregivers and healthcare work- it managed to reduce viral loads at 250 μM when ers are advised to wash their hands frequently and administered immediately after infection or even thoroughly which might be hindered by several up to 24 hours’ post-infection. It also managed to reasons, such as scarcity of running water has oc- fully prevent infection in the hamster model when curred in one of the hospitals in Bangladesh, which administered orally. This was achieved by admin- led to the spread of the infection, by the healthcare istering the drug twice daily, immediately after the workers themselves [34]. Therefore, healthcare infection via the oral route. It managed to prevent professionals are advised to treat any Nipah like the development of any clinical signs even after 42 symptoms as an absolute emergency to prevent the days’ post-infection [32]. spread of the virus [11, 35]. Since vaccines against NiV are not available yet, the most efficient ways to tackle it include creat- Vaccines ing awareness amongst individuals and follow- Initially, recombinant vaccines were used which ing strict preventive measures. These measures provided evidence that could offer include various ways to combat different means complete protection from the virus as NiV enve- of virus transmission which include: food-borne, lope glycoproteins elicited an immune response. animal-to-human and human-to-human routes of Since then, multiple vaccination strategies have transmission. been proposed. Some of these strategies include Nipah virus - the rising epidemic: a review 125

vaccination of swine herds and horses to prevent ing and the consumption of livestock products. spread to human populations; however, these A decade earlier, the consumption of livestock would prove ineffective in countries like Bangla- products had a continuous increase, but after the desh where fruit bats contaminate food sources outbreak, this trend declined quickly addition- too, and hence human vaccines need to be de- ally, since pig export was a significant industry veloped. Nonetheless, ALVAC vectored recombi- in Malaysia, with a total number of 235 million nant canarypox vaccine has shown the potential pigs spread around the country. However, due to to protect pigs and prevent viral shedding. They the epidemic, the number of pigs and farms rap- also resulted in the induction of high antibody idly decreased, bringing the ex-farm price from levels [36]. Another strategy would follow the RM4.29/kg (US$1.03/kg) in September 1998, to current Ebola vaccination approach where stock- RM1.29/kg (US$0.31/kg) in the following April, piled vaccines are deployed for ring vaccination therefore majorly affecting the earnings of farm- around a settlement. ers. Additionally, in order to prevent the virus As of 2018, no large-scale NiV clinical trials have from affecting the mass, 1.1 million pigs were been conducted due to the sporadic nature of out- culled costing about a total of RM280 million breaks of the virus which prevents the conductance (US$66.8 million) of any such trials. Furthermore, the Food and Drug Moreover, multiple other industries were affect- Administration could allow vaccines that predict ed by the outbreak; one sector which suffered the efficacy on animal models to translate to human most was the feed industry, which provides the infections, but no vaccine has been approved for hog raising sector with feeds. The feed industry use as of yet. All candidate NiV vaccines being had a stagnant decline in its production of about developed right now are in the pre-clinical stage RM67 million (US$16 million) [40]. as their effectiveness is still being tested on animal Due to the increasing burden of Nipah around models. Several different vaccines which utilize the globe, several countries have developed in- sG protein and differing adjuvants like oligode- terventions from any future outbreaks happen- oxynucleotide have demonstrated a protective ef- ing in the future, which is an additional econom- fect in animal models. The most effective vaccine ic burden over the countries prevalent to such in this group is the Equivac HeV developed with epidemics. In Bangladesh, many activities such an immune-stimulatory adjuvant. Other vaccines as the cost of creating campaigns, staff cost, ma- using the outer-membrane G/F proteins have also terials pre-testing, field visits, and transportation shown complete protection in hamsters, ferrets, have caused a total damage of 21 million BDT and African Green Monkeys after single injections (US$255,000) [41]. [37]. Furthermore, vectored VSV vaccines are also Therefore, considering the statistics and the no- being developed, and one has shown cross-pro- table economic burden NiV has imposed, if the tection against NiVb and NiVm [38]. The first and outbreaks are not controlled, more farms and only licensed prophylactic treatment for the NiV industries will be affected, creating many future which is available is the previously mentioned troubles. Equivac HeV. It was released in Australia in 2012 and is an equine vaccine [5]. n CONCLUSION It should also be noted that the Coalition for Epidemic Preparedness Innovations (CEPI) has Despite the several warnings in the past two dec- awarded twenty-five million US dollars in fund- ades, regular outbreaks of NiV have led to numer- ing to Profectus BioSciences and Emergent Bi- ous mortalities and morbidities in both humans oSolutions on May 24th, 2018, to collaborate and and animals. Additionally, due to its pandemic develop a vaccine for the NiV. This historic action potential, the prevention of this disease is of crit- has been taken to combat this lethal disease which ical importance due to its capability of causing currently has a mortality rate of 75% [39]. significant physical and economic burden. There- fore, this calls for an urgent need for the health Economic burden authorities to conduct clinical trials in order to In the first outbreak of 1999 in Malaysia, NiV establish possible treatment regimens to prevent had a substantial economic impact on hog rais- any further outbreaks. 126 R.K. Ochani, S. Batra, A. Shaikh, A. Asad

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