Vector-Borne Diseases: JEV and LSD 

Among the problems that flying insects can bring to your stock are some extremely unwanted passengers: Emergency Animal Disease (EADs). 

Two EADs of concern to Australia are Lumpy Skin Disease (LSD) and Japanese encephalitis virus (JEV). Both are notifiable diseases, and both are spread by flying insects acting as ‘vectors’ that carry infection between animals. This article will focus on the relevance of flying insects to disease introduction and spread. 

Lumpy skin disease (LSD) 

The LSD virus is mostly spread by a variety of insects and is largely a concern for cattle producers. Australian flies thought to be ‘vectors’ able to spread it include stable flies, midges and mosquitoes. The insects carry & spread it between animals when they bite. The virus can also be carried on other objects (fomites) e.g., contaminated vehicles, equipment, and clothing it can spread directly from an infected animal or animal products (virus is present in nasal secretions, semen, milk, and blood). 

LSD is exotic and currently not present in Australia. LSD may be introduced here by insects flying or being ‘blown over’ directly from countries in the region where it is present (e.g., Indonesia). Arrival in infected products or via international ports are also possible.  

Grazing cattle and water buffalo in the north would be the likeliest at-risk animals from insects ‘blown over’, but if infection of cattle via fomites or contaminated products occurs anywhere within Australia, then flying insects could further spread the virus. Some LSD strains might infect sheep and goats. It does not infect humans. 

Section 4.2.15 of the AUSVETPLAN Response Strategy – ‘Lumpy Skin Disease’ outlines Australia’s planned response to LSD, which would involve vector (i.e., flying insect) monitoring & control along with vaccination, movement controls, and stamping-out activities. 

Japanese encephalitis virus (JEV)  

The virus that causes JE is transmitted by infected mosquitoes who spread it by biting. It can’t spread without mosquito vectors – i.e., it is not contagious. It’s of most concern if you keep pigs or horses, although evidence of infection with JEV has been found in many other species (cattle, sheep, goats, water buffalo, dogs, flying foxes, and waterbirds). 

JEV has been in the far north of Australia since the ‘90s but in 2021-22 cases were identified in pigs (and humans) across Australia, except for Tasmania and WA. JEV can be spread long distances by the flight and wind dispersal of infected mosquitoes, and by the movement of infected animals who may form a ‘reservoir’ for mosquito transmission (e.g., feral pigs and waterbirds).  

The virus alone does not survive easily in the environment, therefore controlling mosquitoes plays a part in preventing JEV. It is unclear how JEV arrived (perhaps carried by wild birds) but it’s likely that the recent years of wet weather allowed infected mosquitoes to flourish and spread in the south. 

JEV infects and can be dangerous to humans too, so more reason to protect yourself from mozzies – long sleeves, insect repellent etc. See your medical practitioner for advice on vaccination against JEV. For more information including risk to people, see Australia’s official plan AUSVETPLAN Response Strategy – Japanese encephalitis. 

Summary 

Both diseases are spread by flying insects, and both are EADs of national importance. For both, the state or national-level response strategy will involve control of insect vectors in the area where infection has been found.  

However, on a daily basis, vigilance on the farm for suspicious clinical signs in stock animals to allow rapid detection and containment will be important – the sooner the better! The prevalence of insect vectors will affect rate of transmission and spread. Eradication of LSD/ JEV if they become established will be difficult as flying insects form a large and mobile reservoir.  

Planning strategies now to reduce possible new risks from flying insects could be a long-term biosecurity investment for your stock, your staff and yourself.  

Chemical and non-chemical methods should be used together – similar to all anti-parasiticides (including blowfly, lice, and tick treatments), relying on chemicals alone will result in resistance developing.  

Check out these links for other ways to reduce fly numbers on your property: 

How the humble dung beetle keeps down fly numbers: Dung beetle webinar 

For tips on how to reduce areas where flies like to breed: Keep flies out – FlyBoss 

Listen to Paraboss’ Dr Playford, talk about wet weather and insect numbers: ‘Are bugs bogging you down?’ 

For general environmental tips to reduce mosquito breeding & advice on chemical usage (targeted to pigs, due to the recent JEV cases), see: Controlling mosquitoes around piggeries