Anticipating infectious threats to Australia

What are the human, agricultural, wildlife and entomological infectious disease threats to Australia? To answer this questions, the University of Sydney’s Marie Bashir Institute of Infectious Diseases and Biosecurity co-ordinated a “collective brainstorm” session to map out the way forward in assessing and address these future risks.

Moderated by Professor Eddie Holmes, the session included “five top leaders in their respective fields” to provide an overview and discuss recent advances, as well as determining the key challenges with discussion amongst attendees. A fascinating collection of topics and I was fortunate enough to be invited to contribute my knowledge on mosquito-borne disease threats in the Australia region.

Professor Jon Iredell spoke about the development of antibiotic resistance in human pathogens. Most interestingly, he touched on the role humans play in exposing our environment and wildlife to these antibiotics and the resulting impacts on the broader community. Although the issue of antibiotics hasn’t touched my work directly, I’m aware of this issue in relation to the role of constructed wetlands associated with agricultural and urban wastewater facilities. Notwithstanding the direct human health issues, interaction with wildlife may have implications for emerging zoonotic pathogens.

Professor Robert Park spoke about agricultural disease. A fascinating presentation on a topic I wasn’t familiar with but was surprised as to the relevance to exotic vector-borne pathogens. Robert spoke about the Australian Cereal Rust Control Program and how it plays an important role in monitoring the incursions of this fungi.

Dr Karrie Rose spoke about wildlife disease and highlighted some of the issues surrounding the investigation of outbreaks where the environmental, agricultural or human health issues may not be clear from the outset. Additional issues surround the diagnosis of these pathogens and determining the authorities responsible for the outbreak. Karie is the manager of the Australian Registry of Wildlife Health, a program of Taronga Conservation Society Australia and provided a great overview of the diverse nature of zoonotic pathogens, from Chytrid fungus to orbivirus, local authorities must deal with.

Monitoring mosquitoes and the pathogens they're carrying will remain critical in assisting the assessment and management of public health risks in Australia

Monitoring mosquitoes and the pathogens they’re carrying will remain critical in assisting the assessment and management of public health risks in Australia

I spoke about the endemic and exotic mosquito-borne disease threats to Australia, from Ross River virus to dengue. My presentation highlighted issues surrounding globalisation, urbanisation and a changing climate with particular emphasis on the potential introduction of the Asian Tiger Mosquito to mainland Australia and the recent increase in Australian travellers returning home with dengue and chikungunya virus infections. Analysis by WA Health authorities have highlighted the increased risk associated with travel to Bali in recent years. There have also been cases of “airport” or “baggage” dengue, including the first locally acquired cases of dengue in WA for over 70 years as well as a case of infection under similar circumstances near Darwin. The Darwin case was also reported in this PLOS NTD paper. At a time when FNQ is experiencing multiple outbreaks of dengue, there seems to be ever increasing opportunities for the pathogens and vectors to be entering mainland Australia.

You can catch up on the slides from my presentation below:

and a collection of tweets from the session collated by @MarieBashirInst is here.

[The photo at the top of this post is taken from the CDC]

Don’t let the “love bugs” bite this Valentine’s Day

What are you taking on your Valentines Day date? Flowers? Chocolates? Clean undies? Don’t forget to pack the insect repellents! There may be more than just “love bugs” about.

I’ve got you under my skin

The human scabies mite (Sarcoptes scabei) is the only arthropod to truly get under our skin. The tiny mite burrows in and feeds on dissolved human tissue in the tunnels they excavate. Itchy yet? Don’t start scratching as that is one way to release mites and infect your friends.  The other way is when mites come to the skin surface to mate. Newly “knocked up” females are usually quick to burrow into the skin but for those that don’t, they’re prime candidates for transfer.

Skin to skin contact is the typical way the mites are spread from person to person. A hand shake probably won’t do it but sexual contact will. Serious problems with scabies are also not uncommon in aged care facilities and can be a serious problem in Aboriginal communities. Even wombats can be infected.

Once infected, symptoms can take up to a month to develop. At that point, the infected person develops an allergic reaction to the mite’s faeces, skin moults, saliva or moulting fluids. The “mite tunnels” may appear as pale grey threadlike marks and often follow natural creases in the skin in areas such as the hands, particularly the webbing between the fingers, but also on the wrists, elbows, genitals and breasts. Large areas of the body can also be covered by a rash that is not specifically associated with the mite’s burrows but rather is thought to be a generalised allergic reaction. Severe itching all over the body can be experience with the intensity of irritation especially noticeable at night.

Typical scabies infestations are easily treated with an insecticide cream. Problem is, to confirm infection, you need to have a “skin scraping” taking to look for the mites, their eggs or faeces. Taking a “skin scraping” can be pretty nasty and the bulk of scabies infestations are diagnosed on symptoms alone. I think scabies infection is one of the most over diagnosed illness doing the rounds. From the calls I take (at least a couple a week), anyone who presents to their doctor or pharmacist with an itch appears to end up smearing a cream like this all over themselves. The problem is, when the cream doesn’t fix the itch (because the itch is caused by something other than mites), people may repeat the course of treatment once or twice more (as well as trying “other” solutions). That then leads to self inflicted skin irritation and the cycle continues. Correct diagnosis would avoid these problems!

Scabies infection can be even more serious in immunocompromised or elderly individuals when mite populations explode. Known as “crusted” or “Norwegian” scabies, the skin can take on a thicken appearance and contain huge numbers of mites. In these situations, the condition can be highly contagious and barrier nursing is required.


Intense activity of scabies mite in a case of “crusted” scabies (Photo: Stephen Doggett, Medical Entomology, Pathology West)

The “deadliest catch” on the dating scene or just “butterflies of love”?

Pubic lice, Pthirus pubis, (commonly known as crabs) have found a home on the pubic hair of humans (after apparently making the leap from gorillas around 3.3 million years ago). Different to head lice (Pediculus capitis), the claws of pubic lice are adapted to courser hair pubic region and lice and rarely (but occasionally) travel far from those regions. Unsurprisingly, they spread primarily through sexual contact. In many countries they’re classified as a sexually transmitted infection. However, they don’t really pose a significant health risk. They can cause severe itchiness in the infested regions but there are no known pathogens spread by their bites (interestingly though, there has been some suggestion that the presence of pubic lice may indicate the presence of more serious STIs).

You’ve probably seen the headlines. Prompted by this paper, there has been a lot of attention paid to the rise of the Brazilian waxing trend and the threat it poses to the natural habitat of pubic lice. Are the parasite’s days numbered? This probably isn’t the case. No, probably not.

Although there is some data on prevalence rates in Australia from the 1980s (about 1.5% of individuals visiting STI clinics), there really isn’t much more information available about just how widespread are pubic lice infestations (not much quantitative data on pubic hair trends amongst the general population is available either but there have been some attitudinal studies carried out in Australia). Cases of pubic lice is clearly rare but specimens do occasionally pop up in pathology samples submitted to our laboratory. I once tried to look into some data from local sexual health clinics but there just hasn’t been enough data collected to make any meaningful assessment on any changes in prevalence rates.

These days, with information more readily available online, individuals are probably more likely to buy treatments from chemists than attend sexual health clinics. Avenues to collect reliable data on prevalence rates may be difficult to find. Doesn’t seem to matter anyway as the “Brazillian” trend is apparently over. I can hear the tiny applause of crab claws the world over.

Life cycle of the pubic louse (taken from CDC)

Beware the sleepover stowaways

Bed bugs may not specifically be a sexually transmitted arthropod but nevertheless a parasite that may take advantage of some Valentine’s Day sleepovers. Bed bugs have been grabbing the headlines for the past 10-15 years as that make a stunning resurgence in many parts of the world. This resurgence has been attributed to, in some ways, by greater availability of cheap, fast international travel and resistance in bed bugs to commonly used insecticides (I currently have a PhD student investigating this).

Bed bugs don’t live on the body. They don’t just live in beds either. They live in almost any crack or crevice available that is also close to humans. Bedrooms obviously. Planning a special Valentine’s Day sleepover at the local hotel? Don’t be fooled into thinking bed bugs are only found in cheap accommodation, they’re just as likely to be lurking in five star hotels.

If bed bugs decide to make a meal of you, it isn’t just the bites that cause a problem. If they decide to hide away in your overnight bag, you may find yourself dealing with an expensive and inconvenient pest control operation in your home. Best avoid them in the first place.

Best check for any stowaways in Valentine’s Day gifts too.

bedbug_stevedoggettNot the souvenir you were hoping for?

Is your partner rushing home from overseas for Valentine’s Day? Make sure they don’t bring home a less than special gift of mosquitoes or mosquito-borne disease!

As highly unusual as it sounds, transporting infected mosquitoes in luggage has been the cause of infections in non-endemic regions. There have been documented cases of “baggage malaria“. Even in Australia, we’ve had a suspected case of “baggage dengue” in Western Australia. While “airport” malaria and dengue cases have been reported in many regions, perhaps the same rapid international travel that appears to be driving the resurgence in bed bugs may increase the risk of baggage-assisted movement of infected mosquitoes?

Even if your partner manages to avoid bringing home any infected mosquitoes, perhaps a passionate reunion could lead to a highly unusual case of sexually transmitted infection. A scientist working in Senegal returned home to Colorado only to infect his wife with the (normally only) mosquito-borne Zika virus (a virus closely related to Japanese encephalitis virus and West Nile virus rarely recorded outside Africa). Interestingly, we’re currently seeing an outbreak of Zika virus in the Pacific so best be warned if your partner has just returned from French Polynesia!

So, does this mean mosquito-borne viruses like Zika, West Nile, dengue or Ross River could be sexually transmitted human-to-human? We know viruses are sexually transmitted between mosquitoes but apart from the case of Zika virus infection discussed here, I’m not aware of any other reported cases in humans. Strange given the huge numbers of cases that occur during dengue outbreaks. Perhaps nobody has thought to check? The semen of boars has been checked and they found Japanese encephalitis virus….

Wild pig (Sus scrofa) (Photo National Aeronautics and Space Administration)

Who would have thought there were so many entomological risks associated with Valentine’s Day?

To find out more about arthropods of public health concern in Australia, check out this document I put together for the Australian Federal Government Department of Health and Aging. It is available for free download as either PDF or WORD versions.

Webb CE, Doggett SL and Russell RC. (2013). Arthropod pests of public health significance in Australia. Department of Health and Aging, Canberra. ISBN: 9781742419770. [PDF]

(Photo of the Alaskan King Red Crab at the top of this post is taken from Wikipedia.)

World Wetlands Day: Rehabilitation, Agriculture and Mosquitoes

hexham_floodgatesWetlands are some of the most important, but most threatened ecosystems in the world. February 2 is World Wetlands Day and an opportunity to celebrate local wetlands and raise awareness of their importance. Can we rehabilitate wetlands without creating more opportunities for mosquitoes?

What is World Wetlands Day?

World Wetlands Day is celebrated each year on 2 February and marks the anniversary of the signing of the Convention on Wetlands of International Importance in Ramsar, Iran, on 2 February 1971.

As described by the Australian Department of the Environment:

“World Wetlands Day was first celebrated in 1997. Since then government agencies, non-government organisations and community groups have celebrated World Wetlands Day by undertaking actions to raise public awareness of wetland values and benefits and promote the conservation and wise use of wetlands.”

The 2014 theme for World Wetlands Day is “Wetlands and Agriculture” and may, at first, seem a little unusual. However, wetlands play a critical role in supporting many agricultural pursuits by improving water quality and assisting water conservation, providing a buffer against flood and storm events, assisting nutrient removal from runoff and supporting populations of predators of agricultural pests.

rushesWetlands, agriculture and Australia

Wetlands, although important in many ways to local communities and economies, have not always had a healthy relationship with agriculture in Australia. Draining, filling and polluting of wetlands have all resulted from agricultural development in both coastal and inland regions of Australia. Debate regarding the allocation of inland river flows to environmental and agricultural uses continues today. However, there is an increasing awareness of the need to balance the interests of agriculture and wetland conservation in many regions and an integrated approach is required. Fortunately, many land owners are now actively engaged in sustainable land management practices and efforts are made to limit impacts to onsite and offsite wetlands.

Looking ahead, there are new opportunities too. There is much potential in carbon farming or “blue carbon” that may see an increase in wetland areas. At the least, this may provide a valuable opportunity to assign an economic value to our wetlands, something that is often difficult to achieve but may eventually help with their conservation.

Historically, coastal floodplains have been significantly impacted by flood mitigation, agriculture and urban development. Most importantly, the restriction of tidal flows through the construction of sea walls, levees, roads, railways and floodgates have substantially altered the hydrology of these environments leading to changes in flora and fauna. In many instances, the “reclaimed” land has been used for agriculture, particularly grazing livestock. The decision to install floodgates may have been driven by concerns regarding potential flooding and to increase available area for grazing, limited consideration appears to have been given to the potential impact on the environment. Over 4000 structures have been identified in NSW alone that influence tidal flows into coastal wetlands.

cowsRehabilitating wetlands impacted by floodgates and restricted tidal flows

Coastal wetlands in Australia are under threat on many fronts so where there are opportunities to rehabilitate degraded habitats, strategies should be implemented to improve environmental health. So, don’t you just open or remove the floodgates?

With tidal flows restricted from these degraded habitats for decades, there have been substantial changes in these local environments. Understanding how re-establishing tidal flows may impact the existing flora and fauna across the local estuary is critical.

One of the largest estuarine wetland rehabilitation projects in the southern hemisphere is the Hexham Swamp Rehabilitation Project near Newcastle, NSW. The wetlands cover approximately 2,000 hectares and rehabilitation plans have been underway for over 30 years. Floodgates were installed in 1971 and have resulted in significant changes to the local vegetation. While remnant areas of saltmarsh and mangrove remained, the exclusion of tidal water, as well as the accumulation of rainfall runoff, shifted the vegetation to a freshwater dominated system. In particular, the wetlands became dominated by extensive stands of Phragmites australis. While these dense stands of vegetation provided habitat for a range of birds, frogs and snakes, with regard to locally important wading birds, the quality of the habitat wasn’t up to scratch. With the loss of coastal saltmarsh a major concern for local authorities, a strategy was developed to reestablish tidal flows to Hexham Swamp.

hexham_grasslandExtensive hydrological model was undertaken to inform the strategy of floodgate openings. However, despite some complex modeling to predict how tidal waters would move into and out of the system, it really wasn’t until the floodgates were opened that the wetland hydrology could be measured. A staged opening of floodgates over a number of years was undertaken with all gates open in August 2013.

There has already been a dramatic change in the local environment. In areas where tides are now penetrating and increasing salinity, there has been a substantial die off in freshwater vegetation. This is now steadily being replaced with estuarine plants such as saltmarsh. There has been a big shift in the birds visiting the site too with an increase in waders in many areas. There are more fish and an increase in prawn populations in the local estuary has been credited to the openings of the flood gates.

redmudflatWhat about the mosquitoes?

It will come as no surprise that concerns regarding potential increases in mosquito populations were expressed at early stages of this rehabilitation plan. There were some key site-specific issues to consider here. Firstly, the Hunter estuary contains extensive existing and productive mosquito habitats. Hexham Swamp, while significant, is surrounded by a number of other extensive saltmarsh and mangrove environments that are well documented as productive habitats for the saltmarsh mosquito, Aedes vigilax.

The impacts of these saltmarsh mosquitoes as important vectors of Ross River virus, prompted the formation of the “Living with Mosquitoes” group. This group contains five adjacent local governments, as well as a number of other stakeholders, with oversight from the local health district. The group assists local authorities develop coordinated surveillance and community education programs to raise awareness of mosquito risk. Even without changes in the mosquito populations produced from Hexham Swamp, the region would still have an ongoing mosquito issue to address.

Tracking the mosquito populations and changes in their diversity and abundance with the reintroduction of tidal flows, a couple of key observations were made. Firstly, there was a dramatic decline in the abundance of “freshwater” mosquito populations. This was expected and it was hoping that any declines in freshwater mosquitoes would offset any increases in estuarine mosquitoes. Secondly, although an initial “first flush” of mosquitoes were produced following the introduction of tides, populations appear to have stabilsed (perhaps even fallen) in line with other habitats in the local estuary.

The factors contributing to the “first flush” are not completely understood but the most likely scenario is that an accumulation of mosquito eggs over previous years were laying in wait for those first big tides to flood in. Although some of these eggs would have hatched following major rainfall events, there would rarely have been the volume of water in the wetland following rainfall compared to the major tidal flooding events now the gates are open.

mangrovesOur experiences with the Hexham Swamp rehabilitation program show that it is possible to “bring back” estuarine wetlands that may have almost disappeared through the restriction of tidal flows and damaged caused by agriculture (particularly cattle grazing). It is also possible to improve the health of these wetlands without creating additional or increased mosquito problems. Surveillance and planning (and perhaps a little mosquito control) will be required but it appears that if the health of the wetland improves, mosquitoes can be maintained at reasonable levels. It is important to remember that mosquitoes are a natural part of Australia’s wetlands and eradication should never be an objective of management.

Have fun during World Wetlands Day 2014! Don’t forget to check out the free eBook on managing urban wetlands produced by the Sydney Olympic Park Authority.