History and exam

Key diagnostic factors

common

presence of risk factors

Key risk factors include history of travel to an endemic area, contact with known infected human, and consumption of contaminated date palm products in endemic area.

fever

Fever is a universal feature of Nipah virus (NiV) infection: 97% of patients in the Malaysian outbreak had fever at presentation and 100% of patients in Bangladesh outbreaks were feverish during the course of the illness.[22][23][37] Having a temperature >37.8°C was associated with a poor prognosis in Bangladesh outbreaks.[37]

Very few human Hendra virus (HeV) infections have occurred, but fever appears to be common.[29][47][48]

Other diagnostic factors

common

headache

Headache is a common feature seen in both NiV and HeV infection as part of an encephalitic syndrome.[22][23][29][37][47][48] 

Patients with HeV appear to present predominantly with an influenza-like illness with headache.[29]

dizziness

Reported in one third of patients presenting with NiV in Malaysia.[22][23]

weakness/lethargy

Reported in 19% of patients in the Malaysian NiV outbreak.[23]

vomiting

In the Malaysian outbreak of NiV, 27% to 36% of patients presented with vomiting.[22][23]

myalgia

Appears to be a common presenting symptom in HeV as part of an influenza-like illness.[29]

Less common presenting symptom in NiV, reported in only 12% of cases in the Malaysian outbreak.[22]

non-productive cough

Cough was reported in 62% with NiV illness in Bangladesh outbreaks.[23] Less patients had a cough at presentation in the Malaysian outbreak.[22]

Not clear how common cough is in HeV infection.

dyspnoea

Respiratory signs and symptoms, including dyspnoea and acute respiratory distress syndrome, may occur with or without an encephalitic syndrome.[37]

altered mental status/reduced consciousness

Very common, particularly as infection progresses.[22][29][37][47][48] Altered level of consciousness was associated with a poor outcome in Bangladesh outbreaks.[37]

meningism

Only 12% to 28% of patients with NiV presented with neck stiffness and/or meningism respectively in the Malaysian outbreak,suggesting that encephalitis rather than meningitis is the predominant pathological process.[22][23]

seizures

Occur in 23% to 27% of patients with NiV infection.[22][23][37] 

Seizures have been reported with HeV encephalitis.[29]

focal neurological signs

Areflexia and/or hyporeflexia appear to be common in NiV.[22][23][37] Segmental myoclonus was relatively common in the Malaysian outbreak and associated with a poor prognosis, but has not been observed in Bangladesh outbreaks.[22][23] Abnormal plantar response was associated with a poorer prognosis in the Bangladesh outbreaks.[37]

Neurological signs associated with encephalitis have also been reported in HeV infection.[29]

tachycardia

Signs of autonomic dysfunction, such as tachycardia, were relatively common in the Malaysian NiV outbreak and associated with poorer outcome.[23] This has not been seen in Bangladesh reports.[37]

hypertension

Signs of autonomic dysfunction, such as a hypertension, were relatively common in the Malaysian NiV outbreak and associated with poorer outcome.[23] This has not been seen in Bangladesh reports.[37]

Risk factors

strong

history of residence in or travel to endemic area

Nipah virus (NiV) outbreaks occur in Bangladesh almost every year.[5] Other areas with known previous outbreaks include Singapore and Malaysia (where the virus was first discovered in 1998-1999), India, and the Philippines (probable NiV outbreak).[7][11][8][9] The geographical spread of the Pteropus fruit bat, the natural hosts for NiV, is from Southeast Asia and northern Australia through to West Africa. Thus, there is potential for outbreaks in many other areas.[14]

All cases of Hendra virus (HeV) infection to date have been in Australia.[13] In total, only 7 human cases have occurred (as of July 2016); therefore, this remains a very rare human disease.[13] As with NiV, the natural hosts of HeV are also Pteropus bats; thus, there is potential for outbreaks elsewhere.

contact with known infected person

Human-to-human transmission of NiV has been well reported, especially in Bangladesh outbreaks.[24] However, there is no evidence of human-to-human transmission of HeV.[13]

consumption of contaminated date palm products in endemic areas

Consumption of date palm sap in an endemic area has been a major risk factor for NiV in Bangladesh and Indian outbreaks.[20] This is due to date palm sap becoming contaminated by the saliva or urine of NiV-infected bats.[17][28]

weak

contact with horses in endemic areas

Horses are intermediate hosts of both HeV and NiV. Contact with horses is the predominant risk factor for HeV infection.[13] Importantly, the contact may be with apparently 'well' horses; epidemiological data suggest that horses are infectious from 72 hours before onset of HeV signs or symptoms up to and including effective disposal of the carcass.[29]

Given that HeV and NiV are rare and contact with horses is common, the association for an individual is weak. However, the risk clearly rises during an outbreak and where the contact is with a sick horse.

contact with pigs in endemic areas

Contact with pigs was the main risk factor for the NiV outbreak in Malaysia and Singapore (with pig farmers and abattoir workers predominantly affected).[22][23] However, contact with pigs is very common in such areas and so the association for an individual is weak. Exposure to sick pigs has a stronger association with disease.

contact with bats or their secretions in endemic areas

There is evidence of NiV transmitted by direct contact with bat secretions, particularly from outbreaks in Bangladesh.[21] In one outbreak, climbing trees was associated with higher risk, thought to be explained by contact with bat secretions.[19][21] Given that the potential for contact with bats is common, the association for an individual is weak only.

There is no evidence of HeV transmission directly from bats to humans.[13]

diabetes

Has been associated with poorer outcome in NiV infection.[23]

age >40 years

Has been associated with poorer outcome in NiV infection.[23]

bioterrorism

Both HeV and NiV are classified as select agents in the US as they have the potential to pose a severe threat to both human and animal health, to plant health, or to animal and plant products.[30]

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