Нипах вирусы: Таралуы, симптомдары және географиясы

Species of virus

Nipah virus is a bat borne, zoonotic virus that causes Nipah virus infection in humans and other animals, a disease with a very high mortality rate (40 75%). Numerous disease outbreaks caused by Nipah virus have occurred in South East Africa and Southeast Asia. Nipah virus belongs to the genus Henipavirus along with the Hendra virus, which has also caused disease outbreaks. The enveloped virus particles are variable in shape, and can be filamentous or spherical; they contain a helical nucleocapsid. Each head consists of a beta propeller structure with six blades. There are three unique folding patterns of the heads, resulting in a 2 up/2 down configuration where two heads are positioned distal to the virus and two heads are proximal. Due to the folding patterns and subsequent arrangement of the heads, only one of the four heads is positioned with its binding site accessible to associate with the host B2/B3 receptor. The F glycoprotein forms a trimer, which mediates membrane fusion. Ephrin sub types have a complex distribution of expression throughout the body, where the B3 is noted to have particularly high expression in some forebrain sub regions.

Nipah virus has been isolated from Lyle's flying fox (Pteropus lylei) in Cambodia and viral RNA found in urine and saliva from P. lylei and Horsfield's roundleaf bat (Hipposideros larvatus) in Thailand. Ineffective forms of the virus has also been isolated from environmental samples of bat urine and partially eaten fruit in Malaysia. Antibodies to henipaviruses have also been found in fruit bats in Madagascar (Pteropus rufus, Eidolon dupreanum) and Ghana (Eidolon helvum) indicating a wide geographic distribution of the viruses. No infection of humans or other species have been observed in Cambodia, Thailand or Africa as of May 2018. In September 2023, India reported at least five infections and two deaths.

The first cases of Nipah virus infection were identified in 1998, when an outbreak of neurological and respiratory disease on pig farms in peninsular Malaysia caused 265 human cases, with 108 deaths. The virus was isolated the following year in 1999. This outbreak resulted in the culling of one million pigs. In Singapore, 11 cases, including one death, occurred in abattoir workers exposed to pigs imported from the affected Malaysian farms. The name "Nipah" refers to the place, Sungai Nipah (literally nipah river') in Port Dickson, Negeri Sembilan, the source of the human case from which Nipah virus was first isolated. The outbreak was originally mistaken for Japanese encephalitis, but physicians in the area noted that persons who had been vaccinated against Japanese encephalitis were not protected in the epidemic, and the number of cases among adults was unusual. Although these observations were recorded in the first month of the outbreak, the Ministry of Health failed to take them into account, and launched a nationwide campaign to educate people on the dangers of Japanese encephalitis and its vector, Culex mosquitoes. Symptoms of infection from the Malaysian outbreak were primarily encephalitic in humans and respiratory in pigs. Later outbreaks have caused respiratory illness in humans, increasing the likelihood of human to human transmission and indicating the existence of more dangerous strains of the virus. During the 1999 outbreak of Nipah virus, which occurred among pig farmers, the majority of human infections stemmed from direct contact with sick pigs and the unprotected handling of secretions from the pigs. Based on seroprevalence data and virus isolations, the primary reservoir for Nipah virus was identified as Pteropid fruit bats, including Pteropus vampyrus (large flying fox), and Pteropus hypomelanus (small flying fox), both found in Malaysia. The transmission of Nipah virus from flying foxes to pigs is thought to be due to an increasing overlap between bat habitats and piggeries in peninsular Malaysia. In one outbreak, fruit orchards were in close proximity to the piggery, allowing the spillage of urine, faeces and partially eaten fruit onto the pigs. Retrospective studies demonstrate that viral spillover into pigs may have been occurring, undetected, in Malaysia since 1996. Nipah virus is one of several viruses identified by WHO as a potential cause of future epidemics in a new plan developed after the Ebola epidemic for urgent research and development toward new diagnostic tests, vaccines and medicines.

Presently, there are no dedicated drugs or vaccines available for the treatment or prevention of Nipah virus infection. The World Health Organization (WHO) has designated Nipah virus as a priority disease within the WHO Research and Development Blueprint. In cases of severe respiratory and neurological complications resulting from Nipah virus infection, healthcare professionals advise intensive supportive care as the primary treatment approach.

Nipah virus infection outbreaks have been reported in Malaysia, Singapore, Bangladesh and India. The highest mortality due to Nipah virus infection has occurred in Bangladesh, where outbreaks are typically seen in winter. Nipah virus first appeared in 1998, in peninsular Malaysia in pigs and pig farmers. By mid 1999, more than 265 human cases of encephalitis, including 105 deaths, had been reported in Malaysia, and 11 cases of either encephalitis or respiratory illness with one fatality were reported in Singapore. In 2001, Nipah virus was reported from Meherpur District, Bangladesh and Siliguri, India. In September 2021, Nipah virus resurfaced in Kerala, India claiming the life of a 12 year old boy. The most recent outbreak of Nipah virus occurred during January and February 2023 in Bangladesh with a total of 11 cases (ten confirmed, one probable) resulting in 8 deaths, a case fatality rate of 73%. This outbreak resulted in the highest number of cases reported since 2015 in Bangladesh, and ten of the 11 cases during the 2023 outbreak had a confirmed history of consuming date palm sap.