It’s summer and one should guard oneself against mosquito-borne diseases like West Nile Virus (WNV). Belonging to the Japanese encephalitis antigenic complex of the family Flaviviridae, WMV can cause neurological disease and even death.
By Team Double Helical
After the confirmation of a report that claims a seven-year-old boy from Malappuram District of Kerala died of West Nile Virus (WNV), a mosquito-borne disease, Union Minister of Health and Family Welfare J P Nadda is closely monitoring the situation and has spoken to the State Health Minister of Kerala in this regard.
Nadda has directed for all support to be extended to Kerala in the prevention and management of the virus. Secretary (HFW) held a meeting with Additional Chief Secretary Rajeev Sadanandan, Kerala and reviewed the situation. The Health Ministry has dispatched a multi-disciplinary Central team from National Centre for Disease Control (NCDC). The Central team includes Dr. Ruchi Jain, RHO Trivandrum, Dr Suneet Kaur, Assistant Director, NCDC, Dr E Rajendran, Entomologist, NCDC, Calicut and Dr Binoy Basu, EIS Officer, NCDC. The team will support the state health authorities in managing the disease.
The Indian Council of Medical Research (ICMR) has also been alerted and a close watch is being maintained at the Central and the state level. There are no reports available so far for spread of this virus in other parts of the country.
What is West Nile virus (WNV?)
WNV is the leading cause of mosquito-borne disease in the continental United States. It is most commonly spread to people by the bite of an infected mosquito. Cases of WNV occur during mosquito season, which starts in the Summer and continues through Fall. There are no vaccines to prevent or medications to treat WNV in people. Fortunately, most people infected with WNV do not feel sick. About 1 in 5 people who are infected develop a fever and other symptoms. About 1 out of 150 infected people develop a serious, sometimes fatal, illness. You can reduce your risk of WNV by using insect repellent and wearing long-sleeved shirts and long pants to prevent mosquito bites.
WNV is a member of the flavivirus genus and belongs to the Japanese encephalitis antigenic complex of the family Flaviviridae. It can cause neurological disease and death in people. WNV is commonly found in Africa, Europe, the Middle East, North America and West Asia. WNV is maintained in nature in a cycle involving transmission between birds and mosquitoes. Humans, horses and other mammals can be infected.
The WHO says that about 20 per cent of the people who become infected with WNV will develop West Nile fever. Symptoms include fever, headache, tiredness, and body aches, nausea, vomiting, occasionally with a skin rash (on the trunk of the body) and swollen lymph glands.
The WHO regional office for Europe and WHO region of the Americas are intensively supporting WNV surveillance and outbreak response activities respectively in Europe and in North America, Latin America and the Caribbean, together with country offices and international partners.
Generally no symptoms have been observed in most people. Most people (8 out of 10) infected with WNV do not develop any symptoms. However, there is Febrile illness (fever) in some people. About 1 in 5 people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with this type of disease recover completely, but fatigue and weakness can last for weeks or months.
According to Dr Vinay Aggarwal, Past National, Indian Medical Association, “Of course sometimes there are serious symptoms in a few people. About 1 in 150 people who are infected develop a severe illness affecting the central nervous system such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord). Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. Severe illness can occur in people of any age; however, people over 60 years of age are at greater risk. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk.”
Recovery from severe illness might take several weeks or months. Some effects to the central nervous system might be permanent. About 1 out of 10 people who develop severe illness affecting the central nervous system die.
Treatment and vaccine
Treatment is supportive for patients with neuro-invasive WNV, often involving hospitalization, intravenous fluids, respiratory support, and prevention of secondary infections. There is no vaccine or specific antiviral treatments for it. Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms. In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.
Vector and animal hosts
WNV is maintained in nature in a mosquito-bird-mosquito transmission cycle. Mosquitoes of the genus Culex are generally considered the principal vectors of WNV, in particular Cx. Pipiens. WNV is maintained in mosquito populations through vertical transmission (adults to eggs).
Birds are the reservoir hosts of WNV. In Europe, Africa, Middle East and Asia, mortality in birds associated with WNV infection is rare. In striking contrast, the virus is highly pathogenic for birds in the Americas. Members of the crow family (Corvidae) are particularly susceptible, but virus has been detected in dead and dying birds of more than 250 species. Birds can be infected by a variety of routes other than mosquito bites, and different species may have different potential for maintaining the transmission cycle.
Horses, just like humans, are “dead-end” hosts, meaning that while they become infected, they do not spread the infection. Symptomatic infections in horses are also rare and generally mild, but can cause neurologic disease, including fatal encephalomyelitis.
Since WNV outbreaks in animals precede human cases, the establishment of an active animal health surveillance system to detect new cases in birds and horses is essential in providing early warning for veterinary and human public health authorities. In the Americas, it is important to help the community by reporting dead birds to local authorities. Vaccines have been developed for horses. Treatment is supportive and consistent with standard veterinary practices for animals infected with a viral agent.
Reducing the risk of infection in people
In the absence of a vaccine, the only way to reduce infection in people is by raising awareness of the risk factors and educating people about the measures they can take to reduce exposure to the virus.
Dr Suneela Garg, Head of Department, Department of Community Medicine, Maulana Azad Medical College, New Delhi, said, “To reduce the risk of mosquito transmission, our efforts should first focus on personal and community protection against mosquito bites through the use of mosquito nets, personal insect repellent, by wearing light coloured clothing (long-sleeved shirts and trousers) and by avoiding outdoor activity at peak biting times. In addition, community programmes should encourage communities to destroy mosquito breeding sites in residential areas. To reduce the risk of animal-to-human transmission, the gloves and other protective clothing should be worn while handling sick animals or their tissues, and during slaughtering and culling procedures. And lastly to reduce the risk of transmission through blood transfusion and organ transplant, blood and organ donation restrictions and laboratory testing should be considered at the time of the outbreak in the affected areas after assessing the local/regional epidemiological situation.”
Effective prevention of human WNV infections depends on the development of comprehensive, integrated mosquito surveillance and control programmes in areas where the virus occurs. Studies should identify local mosquito species that play a role in WNV transmission, including those that might serve as a “bridge” from birds to human beings. Emphasis should be on integrated control measures including source reduction (with community participation), water management, chemicals, and biological control methods.
Preventing infection in health-care settings
According to Dr A K Agarwal, Professor of Excellence Medical Director, Innovation, Apollo Hospital, New Delhi, “The healthcare workers caring for patients with suspected or confirmed WNV infection, or handling specimens from them, should implement standard infection control precautions. Samples taken from people and animals with suspected WNV infection should be handled by trained staff working in suitably equipped laboratories. Human infection is most often the result of bites from infected mosquitoes.”
Dr A K Agarwal, added, “Mosquitoes become infected when they feed on infected birds, which circulate the virus in their blood for a few days. The virus eventually gets into the mosquito’s salivary glands. During later blood meals (when mosquitoes bite), the virus may be injected into humans and animals, where it can multiply and possibly cause illness.”
The virus may also be transmitted through contact with other infected animals, their blood, or other tissues. A very small proportion of human infections have occurred through organ transplant, blood transfusions and breast milk. There is one reported case of transplacental (mother-to-child) WNV transmission.