The Microbiologist nearly fell off his chair.
“What?! Nipah Virus? Who the heck do you think has Nipah Virus?” exclaimed the Microbiologist.
“I have a patient with a headache and confusion and I’ve been reading about the causes of encephalitis and want to treat them in case it is Nipah Virus” the Doctor replied.
The Microbiologist muttered to himself… the only one confused here was surely this Doctor… why did this always happen on a Friday… I’m the only one with a headache…
“Has the patient travelled? Have they had any contact with animals? Have they been in contact with anyone else unwell?” asked the Microbiologist.
“Well no, but Nipah Virus can cause encephalitis so we should rule it out at least” said the Doctor defensively.
The Microbiologist sighed, “let me tell you a bit about Nipah virus….”
It is likely that NiV has been around for a while, but had not been recognised before. In fact it has since been very commonly identified as a mild illness in pigs and even found in clinical samples in Malaysia going back to 1996. Transportation of pigs, as a food source, to other countries has been responsible for a number of outbreaks since 1999. Concerningly outbreaks have also occurred in India and Bangladesh but in these outbreaks there has been no contact with pigs. Even more worryingly in these outbreaks there was evidence of person-to-person transmission by droplets, as well as ingestion of palm juice contaminated with virus from bats; hundreds of cases occurred and the mortality was over 70%.
The most recent outbreak of NiV was in Kerala, India, in May 2018 where 22 people died, mainly contacts of cases or healthcare workers caring for them. Sound familiar?! Many of the “virus hunters” at the time thought NiV could be the next pandemic… some still do.
Another virus, Hendra Virus (HeV), is closely related to NiV and is part of the same family of viruses called the Henipaviviruses [oh look how cute, they have family!!! It’s not cute ECIC]. HeV was first identified in 1994 in Queensland Australia where it caused an outbreak of severe respiratory disease in horses [I think you make this up, Oz and horses!... really?]. Associated with the horse outbreak were 3 human cases, 2 during the initial outbreak and one 13 months later when the virus reactivated to cause fatal encephalitis. There have been four further cases of HeV in humans, all in Australia and all associated with contact with sick horses.
The main reservoir of NiV and HeV is the fruit bat which is an asymptomatic carrier, with pigs and horses being an intermediate host. Studies on bat populations have found evidence of infection in fruit bats all the way from Oceania to the Middle East and Africa. Many animals are susceptible to these viruses including cats, dogs, ferrets, guinea pigs and hamsters… so not even pets are safe.
How does infection with NiV and HeV present?
The incubation period of NiV and HeV is very variable, from 4-32 days. NiV presents as encephalitis; HeV presents as either a respiratory illness or encephalitis.
Infection usually starts as a mild influenza-like illness with fever, headache and sore throat which can progress rapidly to either mild or severe encephalitis, coma, respiratory failure and death in some cases. The mortality is high (around 70%) and 20% of survivors have long-term neurological sequelae. A small number of patients who initially recover go on to relapse months after the initial infection; of those who relapse approximately 20% die.
How are NiV and HeV diagnosed?
The mainstay of diagnosis in acutely ill patients is with PCR on blood or CSF. Tests for NiV and HeV are not common to perform in the UK and should be discussed with a Microbiologist or Infectious Diseases Physician before sending them to the laboratory. In the UK these samples are processed by the Rare and Imported Pathogens Laboratory at Porton Down.
CSF from these patients shows a typical viral encephalitis pattern with raised lymphocytes, slightly raised protein and a normal glucose.
Serology for NiV and HeV is not available in the UK but may be available in other countries where the diagnosis is more common.
How are NiV and HeV treated?
There is no specific treatment for NiV and HeV but there is some evidence to suggest that Ribavirin may reduce mortality from NiV infection but it has no effect against HeV. In a study of 194 cases the mortality in the treated group was 32% compared to 54% in the untreated group, that’s not a “great” treatment result and animal studies have failed to confirm any benefit. There is also some experimental data to suggest an NiV/HeV cross-reactive monoclonal antibody may be of benefit in treatment. However this is still in the early stages of development in a Phase 1 safety study in Australia; it may be available on a named patient basis but I suspect this would need considerable logistical organisation and would involve specialist advice from the experts at Porton Down.
Prevention on NiV and HeV infection
Given the high mortality of NiV and HeV infection and the lack of an effective treatment, prevention becomes critical. In order to prevent exposure people need to be aware of the risks. Abattoir workers, bat conservationists and veterinary surgeons dealing with horses and bats need to take precautions to prevent exposure to potentially infected animal secretions and blood. There should also be no movement of infected animals. A vaccine to protect horses (and therefore also their owners and vets) has been developed and is available in Australia.
Healthcare workers caring for positive or suspected patients are also at HIGH RISK and should use universal and droplet infection control precautions.
- Endotracheal intubation
- Airway suctioning
- Positive pressure ventilation via a face mask
- High frequency oscillatory ventilation
- Central line insertion
- Diagnostic sputum induction
”So, do you think your patient who has no travel history, no contact with animals and no contact with sick people has Nipah Virus?”
“Well no…” replied the Doctor, “but maybe it could be Hendra Virus instead?” they added.
The Microbiologist reached for the Paracetamol, his headache had suddenly got a lot worse, he groaned and replied “why don’t you Nipah-long to the library and try to learn a bit more about the COMMON causes of encephalitis before you ring me again”.
The Microbiology Registrar quietly nipped out to the hospital shop and picked up 2 ice-creams, for her and her Consultant, knowing that this might just save the next poor junior who called on this very, very hot Friday afternoon.
Note: bats play a vital role in keeping our ecosystems in good health. They pollinate flowers and disperse seeds as they forage on nectar and pollen. Bat rehabilitation is a very worthy cause and we do not wish to add to bats negative public opinion. You can find out more about bat conservation here and even volunteer!