Japanese encephalitis virus (JEV) is a mosquito-borne disease that has become an increasing state-wide concern in Australia, especially with recent detections in areas like New South Wales. But did you know that certain animals play a crucial role in the transmission of this virus? Waterbirds and pigs, in particular, are central characters in the spread of this virus, serving as key hosts in the virus's life cycle, allowing it to persist and spread in certain environments.

The recent development of its spread around Australia have highlighted the importance of understanding how the virus spreads, especially as changing weather conditions create perfect breeding grounds for mosquitoes. While JEV is not new to Australia, there is still the need for increased awareness, preventative measures, and vaccination efforts to minimise its impact on public health. 

In this blog, we’ll explore the role of waterbirds and pigs in the JEV transmission cycle,  practical ways to protect yourself (especially if you live near wetlands, work on a piggery), and look at how vaccinations can help communities stay safe from this potentially life-threatening disease.

What is Japanese encephalitis?

Japanese encephalitis (JEV) is a mosquito-borne virus that poses a significant health risk, particularly in regions where mosquitoes and their animal hosts thrive. Japanese encephalitis was first identified in Japan in the 1870s when a disease outbreak caused by an unknown virus led to severe cases of brain inflammation. The virus was isolated and officially identified in the 1930s, marking a significant breakthrough in understanding its transmission and effects.

JEV is primarily found in Southeast Asia, the Pacific Islands, and parts of Australia, but its range has expanded over time due to changing climate conditions and increasing mosquito populations. Large-scale outbreaks have occurred in countries like Japan, India, China, and Vietnam, particularly in rural areas with significant wetland habitats and agricultural activities. In Australia, JEV has a growing presence in regions with favourable conditions for its transmission, such as wetlands and piggeries.

The virus is transmitted through the bite of infected mosquitoes, and while most people who contract JEV remain asymptomatic, a small percentage may develop severe complications, including encephalitis (inflammation of the brain). These severe cases are rare but can have a significant impact, particularly in high-risk areas.

What makes JEV particularly unique is its transmission cycle. It doesn’t spread directly between humans but relies on a complex network of mosquitoes, waterbirds, and pigs to maintain its presence in the environment. 

The role of waterbirds and pigs in JEV transmission

Japanese encephalitis virus (JEV) relies on a complex transmission cycle involving animals, mosquitoes, and humans. At the heart of this cycle are waterbirds and pigs, which play crucial roles in maintaining and amplifying the virus within the environment.

Waterbirds: Nature’s reservoirs

Waterbirds, such as herons, egrets, and other wading birds, are considered the primary reservoirs of JEV. These birds carry the virus in their blood without showing signs of illness, allowing the virus to circulate within their populations undetected. Mosquitoes that feed on these infected waterbirds pick up the virus, becoming carriers capable of transmitting it to other animals and humans.

Wetlands, floodplains, and areas with abundant waterbird populations are hotspots for JEV activity. The close interaction between waterbirds and mosquitoes in these environments creates a perfect breeding ground for the virus to thrive. This is why regions near wetlands often face higher risks of JEV outbreaks.

Pigs: Amplifying hosts

Pigs, on the other hand, serve as amplifying hosts for JEV. When a mosquito bites an infected pig, it ingests blood containing a high concentration of the virus. These elevated levels of the virus in pigs make it more likely for the mosquito to become infected and spread the disease to other hosts.

Unlike waterbirds, pigs play a more active role in increasing the virus’s reach, particularly in agricultural settings where pig farms or piggeries are common. This is why piggery workers and their families, especially those living near these facilities, are considered high-risk groups for JEV exposure.

 

How the cycle works

1. Infected waterbirds and pigs act as reservoirs where the virus multiplies.

2. Mosquitoes feed on the blood of these animals, picking up the virus.

3. The infected mosquito then bites another animal or human, transmitting JEV.

4. Humans and certain animals, such as horses, are considered "dead-end hosts" because they cannot pass the virus back to mosquitoes.

Implications for public health

The role of waterbirds and pigs highlights the interconnected nature of ecosystems and public health. Proximity to wetlands, waterbird habitats, or pig farms increases the risk of JEV transmission, making mosquito control and vaccination critical in these areas.

Preventing the spread of Japanese encephalitis

Preventing the spread of Japanese encephalitis (JEV) requires a combination of personal protection, environmental management, and public health measures. Since JEV is primarily transmitted through mosquitoes, targeting these vectors and their breeding environments is crucial to reducing the risk of outbreaks. Here are the key strategies to prevent the spread of JEV:

Personal protection against mosquito bites

1. Use mosquito repellents: 

Apply repellents containing ingredients like DEET or picaridin on exposed skin and clothing. These create a protective barrier against mosquito bites.

If you’re concerned about the potential effects of DEET or picaridin, natural insect repellents can be a great alternative. When choosing natural options, make sure they are APVMA-approved to ensure they are both safe and effective. Despite being made from natural ingredients, these repellents can still offer strong protection against mosquitoes.

For example, Good Riddance Insect Repellents is an excellent choice for those looking for a natural yet effective solution. Their range includes two variations: Tropical, made with essential oils like citronella and Australian lemon-scented tea tree, and Sensitive, formulated with gentle essential oils like lavender and geranium. The Sensitive variant is particularly suitable for those with sensitive skin and babies over 3 months old.

2. Wear protective clothing: 

Long-sleeved shirts, long pants, socks, and closed shoes help reduce skin exposure to mosquitoes, especially during peak biting times like dusk and dawn.

3. Sleep under mosquito nets: 

In high-risk areas, use insecticide-treated bed nets to prevent mosquito bites while sleeping. In high-risk areas, using insecticide-treated bed nets is an effective way to prevent mosquito bites while sleeping. For babies, especially those under 2 months old who cannot use most insect repellents, mosquito nets are an essential layer of protection. Ensure the net fully covers the baby’s sleeping area, is tucked securely, and has no gaps where mosquitoes can enter. You can also consider using nets specifically designed for bassinets or cribs to provide added safety. 

Controlling mosquito populations

1. Eliminate standing water: Mosquitoes breed in stagnant water. Remove or regularly empty containers like buckets, plant saucers, and old tires around homes and workplaces.

2. Improve drainage: Ensure proper drainage in flood-prone areas to reduce mosquito breeding grounds, especially near wetlands and agricultural areas.

3. Use insecticides and larvicides: Target mosquito breeding sites with safe and approved insecticides or larvicides to kill mosquito larvae before they mature into adults.

Protecting livestock

1. Mosquito-proof pig enclosures: Since pigs are amplifying hosts, protecting them from mosquito bites is critical. Install mosquito nets or screens in pig enclosures to reduce their exposure.

2. Relocate piggeries: Where possible, establish pig farms away from human residential areas to minimise the risk of human exposure.

Vaccination

1. Get vaccinated if eligible: Vaccination is one of the most effective ways to prevent JEV. High-risk individuals, such as those living near wetlands or working with pigs, should prioritise vaccination. You can even get free vaccination for Japanese encephalitis if you’re in one of the Local Government Areas. 

2. Plan in advance: Since vaccine supplies are limited for Japanese encephalitis virus due to global ordering constraints, let your healthcare provider know early if you intend to receive the JEV vaccine.

Conclusion

Japanese encephalitis virus (JEV) may be a growing concern, but with the right knowledge and preventative measures, its risks can be effectively managed. Whether it’s wearing protective clothing, cleaning your surrounding areas, using repellents or mosquito nets, small actions can make a big difference. For those in high-risk areas or specific occupations, vaccination is a vital step in staying protected.

Disclaimer

The information provided in this blog is based on thorough research conducted by our team using trusted and reputable sources, including health authorities. While every effort has been made to ensure the accuracy and relevance of the content, it is intended for informational purposes only and should not be considered as medical advice.

For personalised advice or concerns about Japanese encephalitis, mosquito-borne diseases, or vaccinations, please consult your healthcare provider or local health authority. Always follow official guidelines and recommendations for your safety and wellbeing.

For further resources or information, consult trusted health authorities like the Australian Government Department of Health & Aged Care website.

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Health & Wellbeing Mosquito