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Nipah Virus Disease – A Newly Recognized Viral Zoonosis

Mahendra Pal Jewaro Abdo
Vol 2(3), 65-68
DOI-

Nipah virus infection is a newly recognized emerging viral zoonosis that causes severe disease in both humans and animals.The disease was first identified in 1999 during an outbreak among the pig farmers in Malaysia resulting in many human deaths making it a public health concern. Outbreaks of Nipah virus disease has been reported in Bangladesh, India and Singapore. Pigs can act as amplifying host and the fruit bats of the genus Pteropus serve as the reservoir of Nipah virus.Transmission of virus from the infected pigs to humans usually occur in an occupational settings. Diagnosis can be confirmed by virus isolation, immunohistochemistry, serum neutralization, ELISA and RT-PCR. Humans may also be infected from bats via the contaminated fruit or juice. Domestic animals may get infected mainly by contract with diseased pigs. Protective clothing, pasteurization of date palm juice, thorough cleaning of fruits, proper hand washing,precautions during the collection and shipping of clinical samples, appropriate bio-security and health education to the public will certainly help in the control of Nipah disease. It is emphasized that an animal health surveillance system should be established to detect new cases in order to provide an early warning for the veterinary and human health authorities.


Keywords : Emerging zoonosis Fruit bat Nipah virus Pig Public health Surveillance

Introduction

Nipah virus disease, a newly emerging zoonosis, was first described in 1999 when it caused an outbreak of respiratory and neurological disease on pig farms in Malaysia, resulting in 257 human cases, including 105 human deaths and the culling of one million pigs (CDC, 1999; Field et al., 2001). In Singapore, eleven cases including one death occurred in abattoir workers who were exposed to pigs imported from the affected big farms in Malaysia. Most pigs develop a respiratory disease which is locally known as “one –mile cough “or “barking pig syndrome” (WHO, 2009). It causes severe disease in pigs resulting in significant economic losses for farmers.

The outbreaks of Nipah disease has also seen reported from Bangladesh and India which resulted in high mortality and morbidity (Chadha et al 2006; ICDDR,B,2010). The fruit bats of the family Pteropodidae are the natural host of Nipah virus. Most humans during the initial outbreaks in Malaysia and Singapore resulted from direct contact with sick pigs or their contaminated tissues (Chua, 2003.,WH0, 2009). The present paper delineates the importance of Nipah disease  as an infectious emerging viral zoonosis.

Etiology

The disease is caused by Nipah virus which belongs to the genus Henipavirus,family Paramyxoviridae and order Mononegaviridales (Chua et al; 1999). The genus Henipavirus  contains three established species namely Cedar virus, Hendra virus and Nipah virus. Nipah virus is an enveloped, negative- sense, single –stranded RNA virus and is readily inactivated by soaps, detergents and many disinfectants. Sodium hypochlorite is recommended for the disinfection of pig farms in Malaysia (CFSPH, 2007) . The  name Nipah refers to the place , Kampong Baru Sungai Nipah in Negeri Sembilan state, Malaysia, the source of the human case from which Nipah virus was first isolated (Field et al; 2001).

Host
Disease is frequently encountered in humans and pigs (WH0, 2009). Natural infection is also recorded in the cat, dog, goat, horse and sheep (CFSPH, 2007; Pal, 2007). Experimentally, the infection has seen established in golden hamster, cat and pig. The fruit bats are the natural hosts for Nipah virus. There is no apparent disease in fruit bats (CFSPH, 2007; WHO, 2009).

Transmission

In humans, transmission of Nipah virus infection occurs via respiratory droplets, contact with nasal or throat secretions from the pigs or handling the tissues of sick animal (CFSPH, 2007; Pal, 2007: WH0, 2009). Consumption of raw fruits or raw date palm juice contaminated with saliva or urine from fruit bats was considered the most likely source of infection in Bangladesh and India outbreaks (ICDDR, B, 2005). Person –to – person transmission through close contact with patient’s secretions and excretions during outbreak in Bangladesh and India has also seen recorded (ICDDR, B, 2007). In an outbreak of encephalitis in Siliguri, India, transmission of virus occurred within a health care settings where 75% of cases were observed among the hospital staff visitors (Chadha et al.,2006). The routes of transmission of Nipah virus from fruit bats to domestic animals is uncertain but pigs may be infected by eating fruits that may be contaminated with bat urine or saliva or by drinking contaminated water (CFSPH, 2007). Pigs may act as amplifying hosts and can shed virus in saliva and respiratory secretion. During Malaysian outbreak, transmission on a pig farm seemed to occur by aerosols and direct contact with respiratory secretion. The pig movement was responsible for the spread of virus between farms. As virus can occurs in the kidney, exposure to pig urine can be a risk factor for infection. Transmission in semen and iatrogenic spread by re- used needles has also seen suggested (CFSPH, 2007).The domestic animals may get infected mainly by contact with pigs (CFSPH, 2007).The cat can become infected through contact or by eating the tissues of bat (Pal, 2007).

Clinical Spectrum

Man; Incubation period is usually 4-20 days. However, incubation period may be as short as 2 days or as long as a month. Infection may remain asymptomatic or may produce fatal encephalitis. The infected persons initially develop fever, headache, sore throat, dysphagia , myalgia, nausea, abdominal pain ,cough, vomiting, weakness. This can be followed by drowsiness, dizziness, altered consciousness, blurred vision and encephalitis. About a quarter of the patients have seizures and about 60% become comatose and require mechanical ventilator. In the long term, persistent neurological dysfunctions are observed in more than 15 % of the patients (WHO,2009).The case fatality may range from 40 to 75% (Chua et al, 2002, Siva et al, 2009, WH0,2009).

Animals: In pigs, the incubation period is estimated to be 7 to 14 days. The symptoms in pigs include labored breathing, fever, serous, mucopurulent or blood tinged nasal discharge, Trembling, twitching, muscle spasms, leg weakness, lameness, spastic paresis, head pressing, seizures and abortion (CFSPH, 2007).Mortality rate of up to 40 % is reported in suckling pigs (Pal, 2007).Dogs exhibit the signs of respiratory distress, fever, and mucopurulent discharge from the eyes and nose (CFSPH, 2007). In goats, poor growth, unproductive cough, severe respiratory sings and deaths are recorded (CFSPH, 2007). Jaundice has been observed in cats (Pal, 2007).

Epidemiology

Nipah virus disease is an infectious, fatal, emerging zoonosis with public health and economic importance (Pal, 2007). The first outbreak of Nipah virus disease occurred in 1999 among the pig raisers in Malayisia. Since then, many outbreaks of disease were reported from south Asian countries including Bangladesh, India and Singapore (Chua, 2003., Chadha et al.,2006.,ICDDR,B,2008). The transmission of Nipah virus from infected pigs to humans in outbreaks of disease in Malaysia and Singapore occurred in an occupational setting. Close contact with live pigs was the means of infection nearly in all the human infections. In Bangladesh and India, consumption of fruit or juice contaminated with saliva or urine from infected bat was the chief mode of transmission of Nipah virus disease. Human- to- human transmission of the virus was observed in many cases reported from Bangladesh and India. The primary reservoir for Nipah virus was identified as fruit bats belonging to the genus Pteropus, family Petropodidae (WHO, 2009). The virus has been isolated from Pteropus iylei in Cambodia ; and antibodies to Henipaviruses have also been found in fruit bats in Ghana and Madagascar indicating a wider geographic distribution of virus. However, no infection of human or other animal species have been detected in Cambodia or Africa so far. The increased contact is driven both by human encroached into bat’s territory and also by movement of bats towards human habitation due to changes in food distribution and loss of habitat. There appears to be no clinical disease in fruit bats. It causes severe disease in domestic animals such as pigs, resulting in significant economic loses for farmers (WHO, 2009). Mortality is usually high in young piglets (Pal, 2007).

Diagnosis
Nipah virus disease should be suspected if pigs have an unusual barking cough or if human cases of encephalitis are present (WHO, 2009). In humans, the virus isolation from  the blood, CSF, throat swab, nasal secretion can be attempted in several cell lines including Vero, BHK, RK-13 and porcine spleen cells.  The identification of virus can be done by electron microscopy immunoelectron microscopy or immunohistochemistry. Antibodies to Nipah virus may be detected in serum or CSF by ELISA and serum neutralization tests (Daniels et al 2001; CFSPH, 2007; WHO, 2009). Reverse transcription polymerase chain reaction (RT-PCR) technique is employed in some laboratories for the characterization of Nipah virus (Abu- Baker et al; 2004). Since Nipah virus is classified internationally as a biosecurity level (BSL) 4 agent , it is highly imperative that the public health laboratories must have adequate facilities for diagnosing the virus.

Treatment

There is no specific treatment for Nipah virus disease. The treatment is mostly focused on managing fever and neurological signs. Supportive therapy can be done with aspirin and theophyllines (Pal, 2007). Mechanical ventilator and prevention of secondary infection are necessary for severely sick persons who are hospitalized. However, during an outbreak of Nipah virus infection in Malaysia, ribavirin, an antiviral drug, was tried and the results were encouraging (Chong et al. 2001).This drug may alleviate the symptoms of nausea, vomiting and convulsions. It is emphasized that further studies should be undertaken to develop drugs which can be safety recommended for the management of Nipah virus disease both in humans as well as animals

Prevention and Control

In endemic areas, human beings are advised to avoid contact with pigs and bats. People who come in close contact with diseased animals must wear protective clothing such as face mask, impermeable gloves, goggles and boots. Fruits should be thoroughly cleaned, washed and peeled and freshly collected data palm juice should be boiled or pasteurized before consumption (WHO, 2009). Care should be taken during the collection and shipment of clinical samples from humans and animals. During an outbreak of disease in pigs, immediate quarantine of animals, culling of infected animals, proper disposal of carcasses by burial or incineration, restriction on movement of animals are necessary to reduce the risk of transmission of infection to humans (CFSPH, 2007., Pal, 2007 and WHO, 2009).Cat should not be allowed to eat the tissues of bat and also to enter the food preparation areas (Pal, 2007). Establishment of good surveillance system is imperative to quickly detect outbreak of Nipah virus disease and initiate suitable strategies for its control. Health education to the public about the source of infection, mode of transmission, severity of disease, good personal hygiene and biosecurity measures should be imparted. Recombinant vaccine appears to give promising results in pigs (Weingarlt , 2006). It is hoped that these preventive measures will certainly help to reduce the incidence of Nipah virus disease both in humans and animals.

Acknowledgements

The authors are grateful to Prof. Dr. R.K .Narayan for his valuable comments during the preparation of this manuscript. Thanks are also due to Lemlem for typing the manuscript.

References

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