番茄社区

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NEW ORLEANS -- Two front-line health workers gave blow-by-blow descriptions of infectious disease outbreaks in India and Kenya that killed dozens earlier this year but could have been much worse.

In a late-breaker session at the American Society of Tropical Medicine and Hygiene (ASTMH) annual meeting, Govindakarnavar Arunkumar, PhD, of Manipal Academy of Higher Education in Karnataka, India, gave an insider's view of the Nipah virus outbreak in India's Kerala region that drew international headlines.

Following that talk, Marc-Alain Widdowson, VetMB, MSc, of the CDC's Nairobi office discussed the international effort to contain an outbreak of Rift Valley fever this spring in three Kenyan counties that left 1o dead.

Nipah is both highly contagious and highly lethal, and initial reports of the outbreak generated fears of an emerging catastrophe. Fortunately, as Arunkumar explained, authorities quickly recognized the threat and stamped it out.

Nevertheless, out of 23 people who became infected, 21 died.

At the ASTMH meeting, Arunkumar presented a fascinating timeline of the response. (He and his colleagues also published a Journal of Infectious Diseases last week on the outbreak.)

Although the first Nipah victim became ill on May 2, 2018, and died 3 days later, the fact of an outbreak took more than 2 weeks to emerge. On May 17, that individual's brother was admitted with encephalitis, and his father and an aunt were also admitted with other symptoms. At that point, hospital officials alerted local public health authorities, and the following day test results confirmed that all three had Nipah virus. State and national officials were then informed, and on May 20, an outbreak was officially declared. Resources were mobilized and included continued follow-up (In his ASTMH presentation, Arunkumar did not address how the "index patient" became infected, but his group's journal paper attributed it to contact with infected fruit bats).

Most of the eventual 23 infections were centered on two healthcare facilities a few miles apart near the city of Kozhikode. One was where the initial victims were first treated, and the second was where several were taken for CT exams.

In both cases, the victims included patients in the same wards and caregivers, but -- emphasizing how contagious Nipah can be -- also some individuals who were merely present in a hallway outside the CT imaging room. Arunkumar said that merely passing within 1 meter of a patient coughing appeared to transmit the virus.

Three cases eventually seen at a third location were determined to have been at one of the others earlier. Arunkumar's presentation included a schematic map of wards, exam rooms, and corridors, and the nearly exact times when and victims were believed to have come into proximity with infected patients.

Arunkumar said the fact that visitors were able to roam freely in these remote facilities contributed to the infection's spread. But he also credited the response from all levels of India's government with swiftly bringing it under control.

Rift Valley Fever

Widdowson noted that the outbreak in Kenya was not altogether unexpected. Rift Valley fever is a viral disease that mosquitoes typically transmit to domesticated animals including cattle, camels, sheep, and goats; humans typically develop illness from contact with infected animals, much less often from mosquito bites. Human-to-human transmission has never been documented.

Because it is fundamentally a mosquito-borne illness, Rift Valley fever outbreaks typically occur in conjunction with flooding; the last was seen in 2006-2007. Heavy rainfall this spring put health officials on alert for another outbreak, Widdowson said, and indeed one began to develop in May, picking up speed in June.

Illnesses were concentrated in two rural counties in Kenya's north, a region where the disease had been seen before, but also in a western area near Lake Victoria where previous outbreaks were unknown. A total of 106 cases were counted, 30 of which were lab-confirmed. Ten cases were fatal.

Once the outbreak was recognized, officials tried a number of ways to stop it. The most significant was to inform local populations of the risks involved with touching infected animals or eating their meat. Officials went further and sought to ban the slaughter and sale of all animals in the outbreak areas but, Widdowson said, "we're not sure how effective that was -- people need to eat."

He noted that the number of cases was lower than seen previously, but that may have been an artifact of the surveillance methodology, which included counting only symptomatic cases. Typically, "80% of cases are asymptomatic," he said, and therefore the case counts could have been an underestimate.

He said the disease's emergence in the previously low-risk Lake Victoria region was a major concern, with subsequent risk assessments showing active circulation of the Rift Valley fever virus that may be amplified by "weather changes."