Understanding the Human-to-Human Transmissibility of Nipah
Amesh A. Adalja, MD, FACP, FACEP, FIDSA | May 14, 2019
Among the several emerging infectious diseases that the world faces, Nipah virus is of particular concern. This RNA virus that originates in bats has caused sporadic outbreaks in several Asian countries, resulting in severe disease and death with mortality rates reaching 70%. Bangladesh is one of the countries that regularly reports Nipah cases. While largely considered a zoonotic disease with poor human-to-human transmissibility – the prerequisite for a pandemic – it is not exclusively so. A new study, published in the New England Journal of Medicine, aims to identify risk factors for human-to-human transmission in Bangladesh.
40% of Worldwide Nipah Cases Included
To date, 628 cases of Nipah have been reported globally. This study includes 248 cases that occurred in Bangladesh over a 14-year period. Nikolay and colleagues analyzed data on all confirmed or probable Nipah cases reported between April 2001 and April 2014. Contacts of cases were defined as those who had in-person physical (touching) contact or had verbal contact (ie, in the same room talking with the patient) with a patient within 15 days of disease onset.
The majority of case patients’ source of infection was zoonotic or unknown, with 33% having acquired the infection through person-to-person contact. Most patients were hospitalized and had respiratory symptoms (including cough) or vomiting.
The contacts of 140 of the cases were traced and totaled 2,494 persons. Person-to-person transmission was identified in 1.4% of contacts, none of whom were asymptomatic (as shown by serology). The largest transmission event identified included 5 generations, amounting to 32 cases. Overall, 5% of case patients were responsible for nearly 90% of transmission events, with 9% of patients in total transmitting infection.
Multivariate analysis demonstrated that age greater than 45 years with dyspnea gave rise to the highest reproductive number (R0 = 1.1). Female spouses were most frequently infected, and, not surprisingly, those with longer durations of contact with patients were more likely to be infected, as were those exposed to body fluids.
Optimizing Infection Control Interventions
Nipah is a pathogen that has been given priority status for the development of a vaccine due to its high mortality rate and its ability to spread between humans. This study provides important evidence of Nipah’s ability to spread efficiently between humans. While it appears that human-to-human transmission is not the norm (overall R0 of 0.33), when it does occur it is via body fluids to those who have prolonged contact with older patients with respiratory symptoms – all factors easily identifiable and amenable to infection control procedures such as gloves and handwashing (and contact precautions in healthcare facilities when feasible). There is also some suggestion – as is the case with all communicable infectious diseases – that potential super-spreaders exist. Until a Nipah vaccine is available, it will be essential in future outbreaks to incorporate these findings into outbreak response to prevent spread.
Nikolay B, Salje H, Hossain MJ, et al. Transmission of Nipah virus—14 years of investigations in Bangladesh. N Engl J Med 2019;380(19):1804-1814.