Dengue fever outbreak risk for Brisbane residents from unsealed water tanks — ABC News (Australian Broadcasting Corporation)

Dengue fever outbreak risk for Brisbane residents from unsealed water tanks

Posted May 03, 2019 05:51:13

New research has revealed the typically tropical mosquito species that spreads dengue fever could survive winters in Brisbane, with non-compliant rainwater tanks providing the perfect habitat for the species and risking an outbreak of infectious diseases.

Key points:

  • Previous studies suggested conditions in Brisbane during winter were inhospitable for the Aedes aegypti mosquito
  • But the CSIRO says 70pc of the mosquito species survived to adulthood in rainwater tanks, while 50pc survived in buckets
  • Residents just need to spend five minutes assessing the state of their rainwater tanks to prevent a disease outbreak

The Aedes aegypti mosquito infects hundreds of millions of people across the world each year with dengue, Zika, chikungunya and yellow fever.

Previous studies suggested conditions in Brisbane during winter were inhospitable for the species, but CSIRO findings show that rainwater tanks could provide year-long protection for the mosquito type.

In controlled experiments, researchers simulated Brisbane winter conditions, raising Aedes aegypti larvae in tanks and buckets of water.

Rainwater tanks ‘an ideal container’

CSIRO scientist Brendan Trewin said 70 per cent survived to adulthood in the tanks, while 50 per cent survived in the buckets.

«What we’ve found in rainwater tanks is the large volume of water buffers or sort of minimises the fluctuation in temperature, so they actually are an ideal container for the insect’s juvenile stages,» Dr Trewin said.

«The mosquitoes have to lay their eggs and these juveniles hatch out in water and so we have a higher survival rate compared to other containers.»

He said rainwater tanks, which had been modified to capture more water, were damaged, or from which the outflow had become disconnected, allowed the mosquitoes to move around freely, potentially leading to outbreaks of infectious diseases.

«We’ve seen holes punched in overflows or sieves to increase water flow, but this actually is a large risk, because it means mosquitoes can move in and out of rainwater tanks,» Dr Trewin said.

«Other modifications, such as just leaving the sieve off, can potentially cause a much bigger issue.»

Tanks need to be maintained properly

The CSIRO said in the early 1900s, up to 90 per cent of Brisbane’s population had dengue fever, but in the past few decades there had not been an outbreak.

«The last time Brisbane had significant Aedes aegypti and dengue epidemics they also had a lot of unsealed rainwater tanks,» he said.

«Our research suggests it was the decision to remove these tanks in the 1950s that was one of the keys to driving the disease-carrying mosquito out of the city.

«We are not suggesting that rainwater tanks should be removed, but we think it is important for people to be aware that if their rainwater tanks are not maintained properly, large areas of southern Australia may see the return of the Aedes aegypti and other exotic disease vectors, bringing with them potentially serious implications for Australian public health.»

How to mosquito-proof your tank:

  • Check sieves are at the entrance and overflow with no gaps
  • Check for cracks in plastic tanks
  • Ensure the sieves are not rusted or contain holes
  • Keep gutters leaf-free — mosquitos feed on decaying leaves
  • Check first-flush devices are draining

QIMR Berghofer Medical Research Institute Associate Professor Greg Devine said each year hundreds of people arrived in Australia infected with dengue fever and other infectious diseases, which could be transmitted by the Aedes aegypti.

«These non-compliant tanks pose a real risk of becoming Aedes aegypti habitats and breeding sites, which could lead to outbreaks of dengue, chikungunya and Zika, to a population that has no immunity to these diseases,» he said.

Dr Trewin said if residents spent just five minutes assessing the state of their rainwater tanks, it could help to prevent a catastrophic outbreak.

«Biosecurity is just as important in the backyard as it is at the border — people need to make sure their water tanks are compliant, fully sealed and not capable of allowing mosquitoes in or out of their tanks,» Dr Trewin said.

People living in homes with rainwater tanks are encouraged to check there are sieves at the entrance and overflow and are were no gaps, check for cracks in plastic tanks, make sure the sieves are not rusting and there are no holes, and check that first-flush devices are draining correctly.

Mosquito Piskun — peddler of diseases and troublemaker

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All about Aedes Mosquito (Aedes aegypti)

FACTS: There are thousands of mosquito species living just about anywhere there’s water and temperate climates. Common genera of mosquitoes include Anopheles (a carrier of malaria), Culex (common in the USA and a carrier of West Nile Virus) and Aedes. Aedes aegypti is a species known as the yellow fever mosquito. It lives in the tropics and subtropics including the southern USA. Its worldwide resurgence over the past 30 years now makes it one of the most widely distributed mosquito species. You can distinguish Aedes aegypti from other mosquito species by the white markings on its legs.

While this species of mosquito first became infamous for transmitting yellow fever, Aedes aegypti carries many other infectious viruses such as Dengue fever, Chikungunya, West Nile virus and Zika. The 2015-16 Zika epidemic has primarily been caused by the spread of the Aedes aegypti mosquito.

Spanish for «little fly,» mosquitoes beat their wings up to 600 times per second. The unnerving sound they create differs from species to species, and listening for the right note helps male and female mosquitoes coordinate their social lives to find suitable mates. Only female mosquitoes bite. Their eggs need the proteins in blood to help them develop. The actual sting of a mosquito is rarely painful, and it is seldom even detected. However, the saliva injected to stop blood from clotting provokes the aggravating skin inflammation and itching associated with a bite. Like all mosquitoes, Aedes aegypti are attracted to your body heat and the carbon dioxide you exhale, and they can detect it up to 75 feet away – so you might try holding your breath. Of course, clothing and repellents are a better defense to help avoid this unwelcome little troublemaker.

Chapter 10 Popular Itineraries Asia


Phyllis E. Kozarsky, Pauline Harvey


India is approximately one-third the size of the United States and has 4 times the population (almost 1.3 billion people). This makes it the second most populous country in the world, behind China. Rich in history, vibrant culture, and diversity, India is the birthplace of 4 world religions: Hinduism, Buddhism, Jainism, and Sikhism. Despite the growth of megacities such as Mumbai and Delhi (both more than 20 million people), India’s rural population is still twice that of its urban population. Although India is one of the fastest-growing economies in the world, the literacy rate varies by state (64%–94%), the level of poverty is high, and the life expectancy is about 68 years.

The topography is varied, ranging from tropical beaches to foothills, deserts, and the Himalayan mountains. The north has a more temperate climate, while the south is more tropical year-round. Many travelers prefer India during the winter—November through March, when the temperatures are more agreeable—although some, particularly families with children, must travel during the summer vacation.

See also:  The Most Dangerous Wild Animals You Can Encounter In The US

India is becoming more popular for US travelers, and rates of travel from the United States are increasing. Tourists are flocking to the temples, beaches, and the Taj Mahal, and international business is flourishing. For some new US residents, India remains their homeland, and they make frequent visits to see family and friends. In addition, India has a large and growing medical tourism sector.

Because tourists could not possibly visit all the sites in India during a 2-week holiday, they usually select a part of India for any given trip. A typical itinerary in the north of India includes Delhi, Agra, Varanasi, and cities in Rajasthan, such as Jaipur (the Pink City) and Udaipur. Agra is the home of the Taj Mahal, a breathtaking monument to lost love. Along the northern travel circle, one can stop to enjoy the magnificent bird sanctuary at Keoladeo Ghana and the tiger reserve at Ranthambore (see Map 10-13). Varanasi, sacred to Hindus, Buddhists, and Jains, welcomes Hindu pilgrimages and boasts extraordinary experiences along the Ganges.

A more southern route might swing through Goa and its beautiful beaches along the western coast. What used to be the backdrop for great parties and old-time hippies, Goa has now become a haven for writers and artists, boasting a chic new culture. Mumbai, a common entry point to India, hosts Bollywood, the largest film industry in the world. Kolkata (Calcutta) is considered the cultural capital of the country. Bengaluru (Bangalore) in the south-central region is both the garden city and India’s Silicon Valley. The old seaside town of Kochi (Cochin) shows evidence of its Portuguese heritage, and Hyderabad shows off its old granite fort, many mosques, and bazaars.

Despite the many and varied itineraries, most health recommendations for travelers to India are similar. The incidences of some illnesses, such as those transmitted by mosquitoes, increase during the monsoon season (May–October) with the high temperatures, heavy rains, and the risk of flooding. Some of the most important health considerations of travel to India are for travelers visiting friends and relatives (VFRs). They often do not seek pretravel health advice, since they are returning to their land of origin. But because they may stay in rural areas not often visited by tourists or business people, live in homes, and eat and drink with their families, they are at higher risk of many travel-related illnesses (see Chapter 9, Visiting Friends & Relatives: VFR Travel).

Map 10-13. India destination map


Vaccine-Preventable Diseases

All travelers to India should be up-to-date with routine immunizations and are advised to consider hepatitis B vaccine. Particularly important is making sure that the traveler is immune to measles. India has not had a case of wild poliovirus since early 2011, obtained its polio-free certification from the World Health Organization in March 2014, and celebrated 7 years of being polio-free in January 2018. Polio vaccine is no longer recommended for US travelers to India. However, all travelers (residents and nationals) coming from countries reporting cases of polio should check to see if there is a requirement for a dose of polio vaccine prior to entry into India.


All travelers to India should be protected against hepatitis A (see Chapter 4, Hepatitis A). Although some assume that those born in India would have been exposed to hepatitis A in childhood and thus be immune, this may no longer be true, particularly for younger people. Consider serologic testing for hepatitis A IgG in VFR travelers, or immunize.


More than 80% of typhoid fever cases in the United States are in people who traveled to India or other countries in south Asia (see Chapter 4, Typhoid & Paratyphoid Fever). Thus, even for short-term travel, a typhoid vaccine is recommended. Patients hesitant to be vaccinated may be persuaded by learning that typhoid fever acquired in south Asia is becoming increasingly resistant to quinolone antibiotics, sometimes requiring parenteral therapy.

Paratyphoid fever, a similar disease caused by Salmonella enterica serovar Paratyphi A, B, and C, has become increasingly prevalent in south Asia, but typhoid vaccines are not protective against this infection.


Although there has never been a published case of a traveler acquiring Japanese encephalitis (JE) in India, the disease is present in many parts of the country (see Chapter 4, Japanese Encephalitis). Risk is highest during the monsoon season (from May through October) although the season may be extended or even year-round in some areas, especially in the south. Vaccination is not recommended for the typical 2-week trip most travelers take to see the major tourist sites in urban areas; publicized outbreaks in recent years have not been in typical tourist destinations. JE vaccine is recommended for those planning to spend ≥1 month in endemic areas during the JE virus transmission season. Consider giving JE vaccine to those planning repeated, short-term travel and to those planning short-term travel to periurban areas with an increased risk for JE virus exposure.


India has the highest burden of rabies in the world, with estimates of 18,000–20,000 human cases per year (see Chapter 4, Rabies). Dogs roam in packs in many areas of the country. Unfortunately, human rabies immune globulin is not readily available except in some clinics in major cities. Information about such clinics can be obtained from the website of the International Society of Travel Medicine (

A preexposure rabies vaccine series is not recommended for all travelers to India, and cost may be a consideration. Long-term travelers, expatriates, missionaries, and volunteers may, however, want to obtain preexposure immunization for themselves and their children. Without preexposure rabies vaccination, bitten travelers may have to leave the country to receive postexposure prophylaxis. Encouraging travelers to think about purchasing a medical evacuation insurance policy that will cover travel for recommended rabies postexposure prophylaxis and education about bite avoidance and management should be a part of every pretravel consultation.


Active cholera transmission has been reported from India in recent years. Check the destination page at for current recommendations.


Unlike other countries in Asia, malaria is holoendemic in India (except at elevations >6,562 ft; 2,000 m) and occurs in both rural and urban areas. Rates of Plasmodium falciparum have increased in the last few decades, and chemoprophylaxis is recommended for all destinations. Remind travelers that malaria-transmitting mosquitoes primarily bite between dusk and dawn (see Chapter 2, Yellow Fever Vaccine & Malaria Prophylaxis Information, by Country; Chapter 3, Mosquitoes, Ticks & Other Arthropods; and Chapter 4, Malaria).

Other Infections


Strains of bacteria resistant to most antibiotics have been carried by travelers from India to many other countries, including the United States. High rates of resistance to multiple antibiotics have been shown among gram-negative (Escherichia coli, Klebsiella spp., and Salmonella spp.) and gram-positive (Staphylococcus aureus) bacteria in India. In particular, bacterial resistance to carbapenems, third-generation cephalosporins, fluoroquinolones, and even colistin are becoming more common.


Dengue is endemic to all of India except at high elevation in mountainous regions (see Chapter 4, Dengue). Poorly reported at the local and national levels, large outbreaks continue to occur, including in many urban areas. Incidence is highest during the wet summer season, which includes the monsoon season (May–October). Travelers to India should take measures to protect themselves from daytime mosquito bites to prevent dengue (see Chapter 3, Mosquitoes, Ticks & Other Arthropods).

During the last several years there have been outbreaks of chikungunya, transmitted by day- and night-biting mosquitoes. Symptoms are similar to those of dengue and malaria, although often with severe and persistent arthralgia (see Chapter 4, Chikungunya).

Zika is a risk in India. Because of the risk of birth defects in infants born to women infected with Zika during pregnancy, women who are pregnant or trying to become pregnant should research the most recent recommendations at


Hepatitis E is being recognized more frequently in travelers to India. A traveler who develops symptomatic hepatitis despite being immunized against hepatitis A will likely have hepatitis E.


Diseases other than rabies can be transmitted by animal bites and wounds. Cellulitis, fasciitis, and wound infections can result from the scratch or bite of any animal. Potentially fatal to humans, B virus is carried by macaques (see Chapter 4, B Virus). These Old World monkeys inhabit many of the temples in India, scatter themselves in many tourist gathering places, and are kept as pets. Macaques can be aggressive and often seek food from travelers. When visiting temples, travelers should not carry any food in their hands, pockets, or bags. It is important to stress to travelers that monkeys and other animals should not be approached or handled. If bitten, travelers should seek immediate medical care.

See also:  Tick Repellent Guide, Natural Tick Repellent for Cats

The risk for travelers’ diarrhea is moderate to high in India, with an estimated 30%–50% likelihood of developing diarrhea during a 2-week journey. Discuss self-treatment for diarrheal illness (see Chapter 2, Travelers’ Diarrhea), and remind travelers to practice safe food and water precautions (see Chapter 2, Food & Water Precautions).


India has among the highest prevalence of TB worldwide; approximately one-fourth of all TB cases worldwide occur there. An estimated 2%–3% of newly diagnosed cases are multidrug resistant; a smaller percentage are extensively drug resistant.

Travelers who plan to work in high-risk settings or in crowded institutions (e.g., medical clinics, hospital, prison, or homeless shelter populations) are at risk for TB exposure. Discuss with them the importance of testing before and after travel, and measures for disease prevention. Travelers should have a tuberculin skin test or TB blood test before leaving the United States. If the test is negative, repeat the test 8–10 weeks after the returning from India.

Use of bacillus Calmette-Guérin (BCG) vaccine in health care workers who will have increased risk of tuberculosis during travel has recently been proposed, although this recommendation remains controversial (see Chapter 4, Tuberculosis). Limited access to BCG and lack of expertise in administering the vaccine in the United States are also barriers.


Travelers who have never before ventured into the developing world may be shocked when arriving in India for the first time. The crowds and the intense colors, heat, and smells are striking and invade all the senses at once. It is difficult to enjoy the beauty of the country without being touched by the enormity of its poverty. The close juxtaposition of the old and new is noteworthy. At times this culture shock can be overwhelming (see Chapter 3, Mental Health).

Transportation in India remains problematic. Recommend carrying food and beverages in the event of delays, which are almost inevitable no matter the mode of transport. Traveling by train can be particularly harrowing, having to force one’s way through the crowd and onto the train. Travelers should make sure to keep passports and valuables safe while in crowds.

India’s roadways are some of the most hazardous in the world, with large numbers of traffic-related—including pedestrian—deaths (see Chapter 8, Road & Traffic Safety). Animals, rickshaws, motor scooters, people, bicycles, trucks, and overcrowded buses compete for space in an unregulated free-for-all. Fasten seat belts when riding in cars and wear a helmet when riding bicycles or motorbikes. Advise travelers to avoid overcrowded buses and not to travel by bus into the interior of the country or on curving, mountainous roads. Discourage nighttime driving (in particular, long-distance travel), even when a paid driver has been hired. Air pollution is a problem in the major cities, so those with chronic lung disease or asthma may consider spending time outdoors when there is less traffic or staying in facilities outside major cities (see Chapter 3, Air Quality & Ionizing Radiation).

Medical tourism is a growing industry in India. Many newer medical facilities have opened recently for travelers desiring cardiac, orthopedic, dental, or plastic surgery or transplantations at a substantially lower cost than in the United States. The benefits and hazards require careful examination (see Chapter 9, Medical Tourism). The quality of health care is quite variable in India and depends on the location.

In general, travelers feel safe while in India, although peddlers and promoters are aggressive with tourists. Travelers may want to avoid making eye contact with a peddler or his goods, or they may risk having someone follow them down the street trying to sell them something. In such instances, a firm “no” should suffice. The stress of negotiating one’s way through India makes it a place where having a close traveling companion is important. It is always wise to pay attention to US Department of State advisories in case of issues that arise at some borders, or occasional increases in religious tensions or terrorist activities.

Sweet Itch: Itching for a Cure

There’s nothing appealing about this seasonal skin condition. Here’s what experts know about managing, treating, and preventing sweet itch in horses.

There’s nothing appealing about sweet itch; here’s the latest on managing this chronic skin condition

Sweet itch, seasonal equine dermatitis, Culicoides hypersensitivity, summer dermatitis—they’re all one and the same. So what is this seasonal skin condition, exactly? Biting midges or gnats, namely Culicoides (colloquially known as ‘no-see-ums’), can trigger an allergic reaction when they bite a horse.

It’s not the simple puncture of the skin that causes the reaction but, rather, the insects’ saliva. In the same way some people develop a rash after exposure to certain allergens, but others don’t, some horses become abnormally sensitive—or sensitized—to midge saliva.

“Insect-bite hypersensitivity is the most common allergy in horses,” says Rosanna Marsella, DVM, Dipl. ACVD, professor at the University of Florida’s College of Veterinary Medicine, in Gainesville. Here, she and Julia Miller, DVM, dermatology resident at Cornell University College of Veterinary Medicine, in Ithaca, New York, will share current information about sweet itch prevention and ­treatment.

Little Insect, Big Troublemaker

Culicoides are small, weak-flying insects that can’t cover long distances or fly against a breeze, so they tend to feed at night and live near water.

In many areas sweet itch is seasonal, says Marsella, although where she lives Culicoides are active year-round. In addition, there are many Culicoides species that feed on different parts of the horse. “The species of Culicoides that are present on the farm determine the distribution of lesions on affected horses,” she says. “In a place like Florida we have over 20 different species of Culicoides; the more species present, the more generalized the distribution of lesions on the horse.”

Affected areas of the body might include:

  • Mane and tail;
  • Ventral midline (the center of the belly);
  • Legs;
  • Face and ears; or
  • A combination of these.

Two Conditions and Lots of Allergies

Horses sensitized to Culicoides saliva can develop two types of hypersensitivity. “One (Type 1) is an immediate reaction, which is why some horses may present with hives,” says Marsella. “The other (Type 4) is a delayed reaction, with signs of itch in particular body locations 24 to 48 hours after the bite. These two types of allergies are mediated by different chemicals in the body. Many horses have both.”

Marsella says effective treatment options for Type 1 hypersensitivity include antihistamines, as well as a customized vaccine to desensitize the horse to the allergen. For Type 4 sensitivity a vaccine does not work. “When it comes down to horses with insect allergy, the majority of management is avoidance,” she says.

Further, Culicoides hypersensitivity is rarely a stand-alone condition. “To complicate things, the majority of horses that are sensitized to gnats are also atopic, a genetically inherited condition that occurs in various species, including people, where there is a propensity toward building allergies to whatever comes your way,” Marsella says. “In people, an example is eczema (an itchy skin inflammation): If you have eczema as a child, you may become sensitized to foods, ragweed, trees, pollen, dust. In the management of these horses, it’s important to identify the different components that add to that itch.”

Thankfully, owners of Type 1 horses with multiple allergies have options. “We can design a custom-made vaccine that desensitizes with allergen-specific immunotherapy,” says Marsella.

She explains that the body can make the allergic type of antibodies called immunoglobulin E (IgE) or the more protective immunoglobulin G (IgG) antibodies. The goal of vaccination is to encourage the immune system to switch to the more protective immune response.

“It takes months to reach full efficacy, but it does re-educate the immune system to become tolerant rather than to overreact,” she says.

Buzz Off

To deter the insects that instigate hypersensitivity in your horse, look for a quality repellent. “There are many fly sprays that are not true repellents—they are just insecticides,” says Marsella, which are designed solely to kill. “An insecticide is good for the average horse. It reduces the insect burden, but a horse that is very allergic needs something strong enough that insects won’t land.”

She explains that while product names might suggest effective solutions, you should read the label to understand the repellent’s composition, bearing in mind pyrethrin, a naturally produced insecticide, is not a true repellent. Active ingredients to look for include:

  • 1% permethrin;
  • 0.15% cypermethrin, a synthetic ­pyrethroid;
  • 10% concentrated permethrin marketed for equids and livestock, diluted one part concentrate to 10 parts water to make a 1% solution; and
  • 45% permethrin spot treatment (applied to the poll to repel insects from face and ears).
See also:  What Do Wasps Eat, Western Exterminator

The product should also contain a substance that binds to the hair, particularly when humidity and sweat come into play.

While many product manufacturers advertise long-term coverage, you typically must apply the 1% spray products up to twice daily, says Marsella.

For horses that have developed a sensitivity to chemicals, Marsella recommends neem oil repellents.

Miller says she’s had limited success with topical sprays and recommends focusing on avoidance measures such as full-body fly sheets. While these sheets can help prevent bites, Marsella discourages using them in hot and humid climates. The horse might overheat, creating a warm, moist environment that’s an ideal breeding ground for bacteria. In cooler and drier climates, look for a breathable stretch fabric with neck and belly coverage. Many fly sheets come impregnated with insect repellent, and you can also spray them. But use the fly sheet before sweet itch takes hold; once itchy, the horse will scratch despite the sheet, even rubbing its fibers into his skin, says Marsella.

For face and ear masks, she cautions owners to keep them clean and dry, as wet, dirty fabric might promote secondary bacterial and fungal infections.

Good Horsekeeping

Stable management strategies can help mitigate midges, as well. Because we know Culicoides are poor flyers and most active between dusk and dawn, stabling your horse indoors at night with stall fans and insect screens over doors and windows will reduce the likelihood of encounters. Barn sprayers emitting a permethrin spray at a 0.2%-0.5% concentration might also help, says Marsella. And because water attracts midges and provides them a breeding ground, turn your horse out as far as possible from water sources such as creeks or ponds. Midges do not breeds in manure, however, so, unlike with flies, stall or paddock cleanliness is not an avoidance measure.

She also suggests installing a Mosquito Magnet, a propane-powered device that uses carbon dioxide to lure mosquitoes—and midges—into a trap. “You should locate this in a spot to attract insects that would otherwise go to the horse,” she says. “I live on a river in Florida, and the use of this machine has significantly cut down on the insect burden.”

Both veterinarians agree that preventing Culicoides contact with the horse is at this point the most effective strategy for avoiding sweet itch.

The Trouble With Testing

Currently, testing options to definitively diagnose sweet itch are lacking. “Unfortunately for Culicoides hypersensitivity, the best way to diagnose is the clinical picture,” says Miller, listing signs such as:

  • Lesion seasonality, which is dependent on where you live;
  • Lesion distribution; and
  • Response to removing Culicoides from the horse’s environment.

While some veterinarians have attempted to skin-test for Culicoides hypersensitivity, Marsella says it can be problematic. During this process, the practitioner injects the horse with a Culicoides allergen. Positive horses with the IgE response will react within about 20 minutes. Horses without the IgE response but with Type 4 hypersensitivity won’t respond until 24 hours later. Therefore, an immediate negative skin test does not rule out the disease. Also, Marsella says some horses might show a false positive if they have IgE antibodies against Culicoides, but aren’t showing clinical signs, raising the question of whether it has not yet reached the threshold for a reaction or that not all IgE antibodies cause disease.

“At this point in time, it is not recommended to place too much importance on Culicoides allergy skin testing,” she says.

Blood serum testing (serology), Marsella says, is not a good option for Culicoides hypersensitivity testing, either. “A blood test measures circulating IgE, not what is found in the skin,” she says. “Nobody has demonstrated at this point in time that there is a correlation between what is circulating in the blood and what is in the skin. Studies have shown a skin test and serology many times don’t match.”

Research has also shown serum allergy testing to be inaccurate. “Intradermal allergy testing (in which a dermatologist injects a small amount of allergen into the skin), has variable results in the literature regarding accuracy,” says Miller, explaining that tested horses often react positive to Culicoides because they are fly-bite hypersensitive, not Culicoides hypersensitive.

Therapy Options

Sweet itch treatment options include topical or systemic medications or both, says Marsella. Topical therapies might include the corticosteroids dexamethasone or hydrocortisone, while systemic ­treatment might entail antihistamines for Type 1 hypersensitivity and glucocorticoids for Type 4 hypersensitivity. Oral therapies are not without risk, however.

“Systemic glucocorticoids may cause laminitis,” she says. “We try to use them as little as possible—only when needed, for a short period of time.”

Regular systemic glucocorticoid use can also lead to decreased efficacy over time and increased infection risk due to these drugs’ immunosuppressive nature.

With Type 4 cases that don’t respond to antihistamines and do require steroids, careful management is key to avoid steroid overuse. “Insect allergies can’t be ‘fixed,’ ” says Marsella. “You can manage them, but you can’t cure them at this point in time. Many of these horses have a chronic history, so you need to find a long-term sustainable plan. You may use steroids a few times here and there when acute, but you cannot and should not rely on giving dexamethasone every summer.”

Nevertheless, “you have to nip pruritus (itchiness) in the bud,” says Miller. “A lot of people are afraid of steroids, but you have to treat itchy horses or they will scratch into a secondary infection (e.g., Staphylococcus), which can also be difficult to treat. You have to break the cycle.”

She recommends getting a head start on insect control each year, which in her area of New York is as early as April.

And if you compete with your itchy horse, learn about association-legal dosage and withdrawal times for ­medications.

Supplement for Health Skin

While supplements alone don’t offer Culicoides hypersensitivity solutions, omega fatty acids can help manage skin conditions and atopic disease, says Marsella. “In atopic disease in other species—we know very little about horses—there is a defect of the skin-barrier function, so the skin is drier. In this regard supplementation of fatty acids is beneficial. Fatty acids are not strong enough by themselves to take care of the problem but, if people want to supplement, that’s fine.”

Miller adds that research in dogs has shown omega-3 and -6 fatty acids to be anti-inflammatory, but in horses this effect is only anecdotal.

On the Horizon

While an effective off-the-shelf vaccine against Culicoides hypersensitivity is not yet available, Marsella says research is ongoing. Some scientists are looking at a preventive vaccine, she says, which would be particularly helpful for horses shipping from cooler to warmer climates to prevent hypersensitivity from developing. She says work is also underway to develop a vaccine to address Type 4 hypersensitivity.

Miller describes current Culicoides hypersensitivity work worldwide, including:

  • Scientists working to replicate a purified Culicoides salivary antigen (a substance that induces an immune response in the body, especially the production of antibodies), which could potentially become available as a vaccine for commercial use;
  • Researchers studying which antigen creates an allergic response in horses, as different Culicoides species potentially introduce different antigens;
  • Investigators looking into the effects of injecting a small amount of purified allergen-specific vaccine along the lymphatic nodes; and
  • Scientists examining sublingual (under the tongue) antigen administration via a special bit that allows the substance to linger in the mouth, ultimately being absorbed under the tongue.

Be Proactive

Don’t play the waiting game with Culicoides hypersensitivity. “I encourage people if they have a horse with allergies not to wait until things are out of control,” says Marsella. “At that point it is so difficult to turn the horse around. Many of these strategies work better in a younger individual, also early in the course of the disease, when the animal has not developed 60 different allergies, because it is impossible to desensitize for so many.”

Being proactive and getting help for your horse early allows him to have a better quality of life. “To live itchy is a miserable life,” says Marsella. “Animals can’t talk, but I see some whose quality of life is so bad their whole personality changes. I encourage people to be proactive.”

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