What is Nipah virus?

What is Nipah Virus?

Nipah virus (NiV) is a highly lethal zoonotic paramyxovirus transmitted primarily from fruit bats to humans, causing severe encephalitis and respiratory disease with case fatality rates of 40-75%, and is capable of human-to-human transmission. 1, 2, 3

Viral Classification and Structure

• NiV is a biosafety level-4 pathogen belonging to the genus Henipavirus within the Paramyxoviridae family 1, 4
• The virus has a pleomorphic structure with a single-stranded negative-sense RNA genome encoding six structural proteins and three nonstructural proteins 3
• Two major genetic clades exist: NiV-MY (Malaysia/Cambodia strains) and NiV-BD (Bangladesh/India strains), with differing clinical and epidemiological features 4, 5

Natural Reservoir and Transmission

• Pteropid fruit bats (flying foxes), particularly Pteropus species, serve as the natural reservoir hosts without developing disease 1, 2, 4
• Transmission occurs through multiple routes: bat-to-human via contaminated fruit or bat saliva/excrement, pig-to-human during outbreaks involving livestock, and critically, human-to-human transmission in approximately 50% of cases 1, 6, 2
• The secondary attack rate among household contacts is extraordinarily high at approximately 50%, far exceeding diseases like meningococcal infection (4 per 1,000 contacts) 6
• Intermediate hosts include pigs, horses, and domestic animals, with pigs serving as amplifying hosts particularly in Malaysian outbreaks 1, 2, 7

Clinical Manifestations

• Initial presentation includes fever, headache, altered mental status, dizziness, and vomiting 1
• Neurological features are prominent: myoclonus with characteristic 1:1 relationship to EEG periodic complexes, dystonia, areflexia, and hypotonia indicate severe CNS involvement and poor prognosis 1, 8
• Respiratory manifestations include pneumonitis and severe respiratory illness, particularly in Bangladesh/India strains 1, 2
• MRI demonstrates discrete focal lesions throughout the brain, predominantly in subcortical and deep white matter of cerebral hemispheres 1
• Case fatality rates range from 40-75% depending on healthcare availability, patient condition, and viral strain virulence 2, 3

Geographic Distribution and Epidemiology

• First identified in Kampung Sungai Nipah village, Malaysia in 1998 during an outbreak among pig farmers 1, 4
• Subsequent outbreaks reported in Singapore (1999), Bangladesh, India, and the Philippines 1, 2
• The disease is endemic to South and Southeast Asia, with recurrent outbreaks particularly in Bangladesh and India 2, 5, 7
• Transmission patterns vary geographically based on breeding methods, eating habits, and viral strain characteristics 2

Diagnosis

• Serological testing detects antibodies but may show cross-reactivity with other paramyxoviruses 1
• CSF culture and PCR are diagnostic, though CSF culture sensitivity varies 1
• Molecular methods using RT-PCR from respiratory specimens, throat swabs, and CSF provide specific diagnosis 4, 7
• Multiple enzyme-linked immunosorbent assays have been developed for diagnostic and surveillance purposes 4
• Contact with the CDC Special Pathogens Branch is recommended for suspected cases 1

Treatment and Management

• Supportive care remains the cornerstone of treatment, as no proven effective antiviral therapy exists 1, 8, 5
• Ribavirin has been used investigationally with C-III level evidence, though efficacy remains limited 1, 8
• Early intubation and invasive mechanical ventilation are recommended over prolonged non-invasive ventilation trials in severe hypoxemia, as delays worsen outcomes and increase healthcare worker exposure risk 8
• ICU-level monitoring with continuous assessment of vital signs, oxygen saturation, neurological status, and organ function is mandatory 8
• Aggressive anticonvulsant therapy with continuous EEG monitoring is required for myoclonic seizures and status epilepticus 8
• Nutritional support with high-protein, high-vitamin diets for stable patients, and early enteral or parenteral nutrition for critically ill patients 8

Infection Control

• Healthcare workers must use airborne precautions with N-95 respirators, gowns, aprons, and face shields due to the high risk of nosocomial transmission 8
• Strict biosecurity measures are essential given the 50% secondary attack rate among close contacts 6
• Rapid outbreak detection and implementation of infection control measures are critical for containment 5, 7

Public Health Significance

• The WHO has categorized NiV as a priority pathogen due to its epidemic potential, recurrent outbreaks, and alarming mortality rates 3
• The worldwide distribution of fruit bat reservoirs means potential spillover events cannot be dismissed in new geographic areas 2
• Climate change and anthropogenic habitat modifications may influence bat ecology and increase spillover risk 2, 3
• No licensed vaccines or therapeutics are currently available, though several candidates are under development 4, 5