A Guam visit to battle Zika virus and discover new mosquitoes


There are few places on earth where you can search in water-filled canoes for one of the most dangerous mosquitoes on the planet less than a stone’s throw from tourists posing for selfies alongside their inflatable novelty swans in the nearby lagoon.

Guam is the place to go if you need to tick that off your “to do” list!

I was fortunate to be invited to speak at the Pacific Island Health Officers Association (PIHOA) Regional Zika Summit and Vector Control Workshop in Guam 25-29 June 2017. The theme of the summit was “Break Down the Silos for Preparedness and Management of Emergencies and Disasters in United States Affiliated Islands” and had objectives to critical analyze the regional responses to recent mosquito-borne disease outbreaks while developing policies to strengthening public health emergency response and preparedness systems and capabilities within the region.

The tranquil lagoons of the Pacific Islands may seem a very long way from the hustle and bustle of the busy South American cities that held the 2016 Olympics but just as Zika virus was grabbing the attention of sports reporters everywhere, health authorities active in the Pacific were growing concerned too.


The Pacific has been far from free of mosquito-borne disease outbreaks. Previous outbreaks of dengue, chikungunya and even Ross River virus had struck numerous times. While sometimes widespread, at other times outbreaks were more sporadic or isolated. As is the case for many non-endemic countries, outbreaks are prompted by movement of infected travelers and the prevalence of local mosquitoes.

Across the region there are four mosquitoes of primary concern, Aedes aegypti, Aedes albopictus, Aedes polynesiensis and Aedes hensilli. The greatest concerns are associated with Aedes aegypti and in those countries where the mosquito is present, the risks of mosquito-borne disease outbreak are greatest. For this reason alone, it is imperative that good entomological surveillance data is collected to confirm the distribution of these mosquitoes but also to develop strategies to eradicate, where possible, Aedes aegypti should it be introduced to new jurisdictions.

With a growing interest in developing mosquito surveillance and control programs for exotic mosquitoes here in Australia, it was a perfect opportunity for me to get a closer look at how the threats of these mosquitoes and associated outbreaks of disease are managed.

On the third day of the meeting, vector control took centre stage. A brilliant day of talks from each of the jurisdictions on the disease outbreaks they’ve faced and how they’re preparing for future threats. There were presentations from the United States Affiliated Pacific Islands (USAPI) including Guam, the Federated States of Micronesia (Yap, Kosrea, Chuuk, Pohnpei), the Commonwealth of the Northern Marianas (CNMI), the Republic of Palau, the Republic of Marshall Islands (RMI), and American Samoa.

Hearing from these teams doing their best to protect their local communities from the threat of mosquito-borne disease, with only limited resources, was quite eye opening. There was passion and dedication but each territory faced unique challenges to ensure the burden of disease is minimised.


Just outside the workshop venue were a series of water-filled canoes. Most contained larvae!

There is little doubt that climate variability will have a strong role to play in the impacts of mosquito-borne disease across the region in the future but there are so many other issues that could be contributing to increased risk too. One of the biggest problems is rubbish.

Time and time again, the issue of accumulated waste, especially car bodies and discarded tyres, was raised as a major problem. As many of the key pest mosquitoes love these objects that trap water, treatment of these increasing stockpiles becomes more of a concern. Community wide cleanups can help reduce the sources of many mosquitoes but the rubbish more often than not remains on the island and requires continued management to ensure is not becoming a home to millions of mosquitoes.

It is a reminder that successful mosquito control relies on much more than just insecticides. An integrated approach is critical.

There was a “hands on” session of surveillance and control. Coordinated by PIHOA’s Eileen Jefferies and Elodie Vajda, the workshop was a great success. It provided an opportunity for many to see how to prepare ovitraps and BGS traps (one of the most widely used mosquito traps) and discuss the various considerations for choosing and using the right insecticides to reduce mosquito-borne disease risk. Workshop attendees were also the luck recipients of a selection of cleaver public awareness material produced in Guam, from personal fans and anatomically incorrect plush mosquitoes to Frisbees and mosquito-themes Pokemon cards!


Guam “mozzie” team: Elodie Vajda, Claire Baradi, Michelle Lastimoza, Eileen Jefferies and me

Following the summit, there was a chance to visit the new Guam “Mosquito Laboratory”, newly established as part of the Guam Environmental Public Health Laboratory (GEPHL). I’ll go out of my way to visit any mosquito laboratory but I was particularly keen to see this one as one of my previous students was playing a key role in establishing the mosquito rearing and identification laboratories. Elodie has been doing an amazing job and it was brilliant to geek out with her over some hard core mosquito taxomony as we tried to ID a couple of tricky specimens. [Make sure you check out our recent paper on the potential impact of climate change on malaria outbreaks in Ethiopia]

It actually turned out that one of their “tricky specimens” was a new species record for Guam – an exotic mosquito Wyeomyia mitchellii! The paper reporting this finding has just been published “New Record of Wyeomyia mitchellii (Diptera: Culicidae) on Guam, United States“.


Mosquito-borne disease in the Pacific isn’t going anywhere and it’s important that once the focus fades from Zika virus, dengue and chikungunya viruses will again take centre stage and their potential impacts are significant. With the added risks that come with gaps in the understanding of local pest and vector species, the prevalence of insecticide resistance among local mosquitoes, climate variability and a struggle to secure adequate funding, challenges lay ahead in ensuring the burden of mosquito-borne disease doesn’t increase.

A modified version of this article appears in the latest issue (Winter 2017; 12(1)) of Mosquito Bites Magazine, (a publication of the Mosquito Control Association of Australia)


Does Zika virus pose a threat to Australia?

They’re small, spindly insects but their threat never dwindles – the bites of mosquitoes threaten death and disease in many parts of the world. The emergence of a little-known virus, Zika, from an African forest, is the latest to alarm the public, politicians and health authorities because of its potential link to birth defects.

What is Zika virus?

Zika virus is a mosquito-borne virus closely related to dengue and Yellow Fever viruses. Discovered almost 70 years ago in a Ugandan forest, the virus generally only causes a mild illness. Symptoms include rash, fever, joint pain and conjunctivitis.

Severe symptoms aren’t common and the illness was never thought to be fatal.

Despite detection throughout Africa and Asia, the virus rarely entered the spotlight of scientific research. It was overshadowed by the spread and impact of dengue and chikungunya viruses, which infect millions of people across the regions.

In the last decade, Zika virus outbreaks have occurred in the Pacific, with reports of severe illness. But again, Zika was considered a lesser threat than dengue and chikungunya viruses.

Everything changed in 2015 when Zika virus reached the Americas.

New outbreaks and severe symptoms

Since the first local Zika virus infection, cases have been reported from at least 19 countries or territories in the Americas, with more than one million suspected cases.

Rapid spread of an emerging mosquito-borne pathogen is news enough but people are also panicked by reports of more serious consequences of Zika virus infections, including post-viral Guillain-Barré Syndrome, an autoimmune condition where there person’s nerves are attacked by their own body.

Of most concern has been the rapid rise in rates of microcephaly, a birth defect which causes babies to be born with unusually small heads, in regions where Zika virus has been circulating.

While the role of Zika virus as the cause of microcephaly has not yet been confirmed, there is growing evidence of a connection between the two where pregnant women have been infected with the virus.

Babies born with microcephaly, and those who died shortly after birth, have tested positive for the virus, and there are close regional associations between clusters of birth defects and Zika virus.

There is enough concern for the Centres for Disease Control to issue health warnings to pregnant women planning to travel to these regions. [This also includes the Australian Government] Some health authorities are even advising people to postpone pregnancies.

There is no vaccine for Zika virus. Stopping mosquito bites is the only way to prevent infection.

Is Australia at risk of a Zika virus outbreak?

There is little doubt the virus can make it to Australia. There have already been a number of infections reported in travellers arriving in Australia from the Cook Islands and Indonesia.

Mosquito-borne viruses generally aren’t spread from person to person. Only through the bite of an infected mosquito can the virus be transmitted.

In the case of Zika, there have been some unusual cases of transmission, including through sex and the bite of an infected monkey. Despite these unusual circumstances, mosquitoes will still play the most important role in any local transmission.

While dozens of mosquitoes are capable of spreading local mosquito-borne pathogens, such as Ross River virus, only one of the 300 or so mosquitoes found in Australia can transmit Zika virus: Aedes aegypti, the Yellow Fever Mosquito, which is only found in north Queensland.

The Yellow Fever mosquito, Aedes aegypti, is critical to the spread of Zika virus in many regions of the world, including Australia.

For local Aedes aegypti to spread Zika virus, they must bite an infected traveller shortly after they return from a country where the virus is circulating.

While the chances of this happening are small, there is then a risk of a local outbreak occurring as the infected mosquito bites people who’ve never left the country.

This is the process that occurs in outbreaks of dengue in Far North Queensland. If we can get outbreaks of dengue, there is no reason we cannot, or won’t, get an outbreak of Zika in the future.

How to reduce the risk of transmission

Fortunately, authorities are well placed to contain an outbreak of Zika virus, as the required strategies are the same as management of dengue outbreaks.

Perhaps the real message here for Australian authorities is that they need to work diligently to keep exotic mosquitoes out of the country.

While Aedes aegypti may not become established in southern cities, even with a changing climate, there is great potential that Aedes albopictus, better known as the Asian Tiger Mosquito, could become established in southern cities. As well as a vector of Zika virus, it can spread dengue and chikungunya viruses and be a significant nuisance-biting pest. Keeping this mosquito out of our cities is critical.

Australians planning travel to South and Central America, including the Rio Olympics, should take precautions to avoid mosquito bites. Irrespective of Zika virus, mosquito-borne dengue and chikungunya viruses have infected millions of people, causing thousands of deaths, in the last few years and are reason alone to pack mosquito repellents. Be prepared to cover up with long sleeved shorts and long pants if in regions where risk is high.

The ConversationThis article was originally published on The Conversation. Read the original article.

Chikungunya virus arrives in North America: What does it mean?

aedes_albopictus_SteveDoggettIt was only a matter of time. From the moment the first cases of mosquito-borne chikungunya virus were detected spreading through the Caribbean, authorities were expressing concern about the possible introduction into North America.

Chikungunya virus is a mosquito-borne virus that causes potentially severe illness. Outbreaks have occurred in many parts of the world but, until recently, it hadn’t been reported from the Western Hemisphere.

Since the first reports of chikungunya virus detection among residents of the French side of St. Martin in the Caribbean surfaced in December 2013, there have been over 350,000 cases in Caribbean, Central America and South America. [update 4 September 2014: The total estimated cases now is over 650,000] [update 6 November 2014: Total estimated cases now 750,000] [update 12 December 2014: now over 1 million suspected cases of disease!]

Chikungunya virus isn’t just impacting the Americas, it has been sweeping across the Pacific in 2014 and justifying the work of health authorities in developing strategic response plans.

While recent concern about mosquito-borne disease has focused on the risk of dengue associated with travellers attending the FIFA World Cup in Brazil, the number of imported cases of chikungunya virus into the U.S. has steadily increased with approximately 250 cases being reported this year. There have been imported cases in the past but now a locally acquired case has been reported in Florida.

The most recent update provided by the CDC [6 Novemebr 2014] reports that the total number of returning travellers to the U.S. is now 1,600, a staggering figure when compared to the pre-outbreak average of 28 cases per year. With about 9 million people travelling between the United States and Caribbean each year, the risks of the virus being introduced to the U.S. and triggering additional local outbreaks are not insignificant.

So what does this mean if I live in the U.S. or I’m about to visit?

There have been mosquito-borne pathogens introduced into North America in the past. Most famously was West Nile virus. Introduced in 1999, the virus has spread across the country and in the past 15 years or so infected almost 40,000 people and causing approximately 1,600 deaths.

Will Chikungunya virus so the same? No.

West Nile virus spread so widely because mosquitoes found all  through the U.S. (over 40 different mosquito species) can carry the virus and birds, particularly those associated with urban areas act as reservoirs for the virus. What this means is that the virus could more easily spread amongst local mosquitoes and wildlife. This won’t be the case with chikungunya virus.

There are only two mosquito species associated with the spread of chikungunya virus in the U.S.. Aedes aegypti and Aedes albopictus. These two species are not as widespread or abundant as those that transmit West Nile virus.

Aedes aegypti, the Yellow Fever mosquito, is already a concern. This species is the most important mosquito internationally in the transmission of dengue viruses. It has been responsible for locally acquired cases of dengue in some southern regions of U.S. However, this mosquito is not found in many regions of North America.

Approximate distribution of Aedes aegypti in U.A. (Source CDC)

Approximate distribution of Aedes aegypti in U.A. (Source CDC)

Aedes albopictus, the Asian Tiger Mosquito, has a slightly greater distribution. This mosquito is more tolerant of temperate climates and so is found across many more regions within North America than Aedes aegypti. As Aedes albopictus has been responsible for some explosive outbreaks of chikungunya virus elsewhere in the world, concern was that this species may drive a similar outbreak in North America. Fortunately, some genetic studies have indicated that the current strain of chikungunya virus circulating in the Western Hemisphere is less prone to explosive outbreaks of disease driven by Aedes albopictus. However, these two mosquito species still hold the potential to spread chikungunya virus and should be considered a risk to be managed.

The approximate distribution of Aedes albopictus in the United States based on current data (Source: CDC)

The approximate distribution of Aedes albopictus in the United States based on current data (Source: CDC)

When considering the risk posed by Aedes aegypti and Aedes albopictus, other factors need to be considered. As opposed to West Nile virus, there are no local wildlife hosts of chikungunya virus that will assist the spread of the virus. Chikungunya virus, like dengue viruses, are typically spread by mosquitoes from person to person (as opposed to the spread of West Nile virus by mosquitoes between birds and people). Problem is people are the most likely culprits in spreading the pathogen anyway. They move around a lot too.

While there may be some uncertainty associated with predictions of what will happen regarding chikungunya and Aedes albopictus in the U.S., perhaps for the best indication of what may happen with chikungunya virus is to look at dengue. There have been significant increases in the activity of dengue in South America in recent decades. Notwithstanding the burden of disease on those countries, this increasing activity also increases the risk of infected travellers sparking local outbreaks in North America and has prompted warnings from local authorities. International travel has been identified as a critical issue in the global spread of dengue. However, while travellers are returning to North America infected with dengue, and there have been some locally acquired cases of dengue, there hasn’t been any major outbreaks recently (despite the history of major outbreaks in U.S. prior to the 1940s).

Countries and Territories with Autochthonous Transmission or Imported Cases of Chikungunya Virus Infection, as of August 1, 2014. (Source:  "Chikungunya Virus in the Americas — What a Vectorborne Pathogen Can Do" (NEJM)

Countries and Territories with Autochthonous Transmission or Imported Cases of Chikungunya Virus Infection, as of August 1, 2014. (Source: “Chikungunya Virus in the Americas — What a Vectorborne Pathogen Can Do” (NEJM)

There is little doubt that there will continue to be some more locally acquired cases in Florida or other states where Aedes aegypti or Aedes albopictus are present. The risk will be determined by travellers bringing with them the virus from elsewhere and any reduction in the activity of chikungunya within the Americas will reduce the risk of introduction, and subsequent risk of local cases. A recent study confirmed the importance of Aedes albopictus as a vector with field collected specimens showing a strong preference for human hosts (as opposed to other mammals or birds).

repellent_spraying_webbHow can you reduce the risk?

The two mosquitoes primarily associated with chikungunya virus transmission are associated with water holding containers. These are typically found around the home. Ensuring that opportunities for these mosquitoes are minimised is critical. These mosquitoes can be found in any container that holds water, from pot plant saucers to rainwater tanks and from pet water bowls to water collecting on tarpaulins covering boats or trailers. If you see wrigglers about, tip the water out!

There is no vaccine but the use of mosquito repellents can be an effective prevention strategy. If used correctly, these will provide protection. However, keep in mind that the mosquitoes that transmit chikungunya virus primarily bite during the day (as opposed to the evening like other species). You’ll need to get that repellent on first thing in the morning. You can also read this recent post of mine on how best to combine sunscreens and mosquito repellents.

In summary, there is no need to panic but be prepared and follow the advice provided by the CDC and your local mosquito/vector control authority.

A good summary and analysis of chikungunya activity in the Americas is provided here (thanks to Ramon Martinez). You can also follow some of the coverage at Examiner by Charles Simmins. A perspective on the current (and possibly historic) activity of chikungunya virus in the Western hemisphere is provided in this New England Journal of Medicine piece.

**UPDATE 7 August 2014** There have now been 4 locally acquired cases of chikungunya virus in U.S. (all in Florida) but more importantly, mosquitoes collected locally in Texas have now tested positive to chikungunya virus. Local authorities are responding with extra control activities.

The photograph of Aedes albopictus at the top of this piece is by Stephen Doggett, Medical Entomology, Pathology West ICPMR Westmead.

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