Nipah Virus encephalitis (NiV) is an infectious disease caused by an RNA virus of Paramyxoviridae, genus Henipavirus family. The first incidence of Nipah was detected in 1999 in Sungai Nipah village of Malaysia, when residents in close contact with pigs experienced encephalitis resulting in respiratory illness. Immediate investigations revealed that fruit bats, popularly known as ‘flying foxes’ are natural reservoir hosts of the Nipah and Hendra viruses, generally present in their urine, feces, saliva, and birthing fluids. The 1999 NiV epidemic caused more that 33 per cent deaths of the 300 identified victims in Malaysia and Singapore.
The governments of those countries, in order to prevent the spread of the disease, killed more than one million pigs in the affected pig farms. Such rigorous measure incurred huge financial losses to the pig farmers.
The outbreak in Malaysia caused a loss of 450 million USD due only to the destruction of pig farming. However, reduced medical expenses both at the household and government levels were the indirect benefits that certainly compensated for the loss experienced by the pig farmers and the government.
NiV is one of the many ‘animal to human’ diseases caused by environmental mismanagement.
Investigations revealed that the incidences of NiV occurred in Malaysia in the late nineties of last century due to indiscriminate destruction of millions of hectares of tropical rainforest for promoting animal husbandry, especially piggeries. The ‘slash and burn’ method of forest destruction created smog cover over huge region leading to the destruction of bio-diversity, especially of flora and fauna needed for ‘flying fox’ habitat. This prompted migration of the bats, the reservoirs of the virus, in search of food and shelter to neighboring fruit orchards around the pig farms and human settlements causing the spread of NiV first among the pigs and other animals. The pig-to-pig NiV spread was rapid leading to subsequent spread among the workers in close contact with the pigs. This outbreak killed 40 percent of the affected people in Malaysia before the detection of the virus.
Starting from 2001 NiV casualties were detected in Bangladesh and India which continues in this region for consecutive years till to date. Although the mass and scale of spread of this virus remains confined within small geographical pockets, the fatality rate continues to beconsiderably high. According to WHO during 2001-2012 this ratio averaged at 77 per cent in Bangladesh. The north-western and western districts of Bangladesh are reportedly prone to NiV. As is seen from the Table below, fatality rates in Bangladesh increased continually during 2001-2005, with drastic decrease in 2007 and increase in subsequent years. In 2004 the number of affected people numbered 67 of which 50 (75 per cent) died. The fatality rate was highest in 2005, 92 per cent, followed by 90 per cent in 2011.
Morbidity and Mortality due to NiV in Bangladesh (2001-2012)
Source: WHO
The intensity of public health risks is linked to the level of exposure of the people to virus. In the case of Malaysia and Singapore transmissions occurred via direct human contact with the infected pigs that constituted intermediate hosts, while in Bangladesh the victims were affected by drinking contaminated by the bats raw palm sap, being in contact with bat excrement during collection of palm sap and via human-to-human transmission. Later suggests for special precautions to be undertaken by the health, laboratory and slaughterhouse workers.
The human infection symptoms involve encephalitic disorder manifested primarily by headaches, fever, disorientation, myalgia, vomiting, lethargy, sore throat, dizziness, drowsiness, mental instability, inflammation of brain, unconsciousness and coma leading to death within 24 to 48 hours in case of lack of immediate supportive measures.
The affected people may experience respiratory problems like pneumonia and acute respiratory distress, and seizures. Experiences demonstrate that around a fifth of the survivors of acute encephalitis inevitably suffer from residual neurological damages after recovery.
So far NiV has no medicinal treatment. However,subunit vaccine, using the Hendra G protein, has been recently used in Australia to protect horses against Hendra virus. This vaccine produces cross-protective antibodies against HENV and NiV. It also offers great potential for henipavirus protection in humans. Supportive care for the victims and preventive measures in general are the suggested measures. Since palm sap drinking is a common practice in rural Bangladesh, it is recommended that the sap is boiled at least up to 70 degree Celsius before consumption in order to eliminate the virus. Also the family members of the patients need to refrain from sharing with him/her common household goods: utensils, bed, etc. Close physical contact till complete recovery must be avoided. Policies should be aimed at protecting the natural habitat of the flying foxes with intelligent forestry management. In addition, structured and methodical mass awareness programs need to be conducted by the Ministry of Health in coordination with other ministries and the NGOs in the rural areas. n
