(Bloomberg) -- A father and daughter who were recently infected with bird flu in Cambodia got it from direct exposure to sick animals, health officials said, ruling out the possibility of human-to-human transmission. 

The 11-year-old girl died from the H5N1 virus last month. Her father was subsequently diagnosed, then recovered after being hospitalized to get medical care. Tests on another 51 people, including 20 of their close contacts and 31 who were showing flu-like symptoms, all tested negative, according to a statement from Cambodia’s Ministry of Health. 

“Both cases have been concluded as H5N1 virus transmission from poultry, and this event is NOT a human-to-human transmission,” it read. 

While human infections with the virus known formally as avian influenza remain rare, skyrocketing rates in birds and increasing incursions in mammals have led to concern among scientists and governments that the virus may be mutating in ways that could make it easier to spread.  

Samples of the virus taken from the girl and her father both showed genetic changes that occur when it passes from a bird to a human, according to an analysis conducted at the Institut Pasteur du Cambodge’s virology unit. There was no indication of mutations or adaption that would make it more transmissible among mammals, the agency said. 

Cambodia sent the full genome virus sequence to GISAID, a global repository that tracks pathogens like Covid-19 and avian influenza. The strain found in Cambodia, known as 2.3.2.1c, is the one that’s been dominant in Southeast Asia for years, the group said, and differs from the 2.3.4.4b clade that’s currently circulating in most other part of the world. 

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