The Zika Virus

The Zika virus, transmitted by mosquitoes, has captured headlines recently and set off something of a panic. This is technically not a "new" virus, as it was first discovered in the course of researching yellow fever in Africa in 1947. A rhesus monkey, caged near the Zika Forest in Uganda, contracted a fever of unknown origin, later (1952) determined to be caused by what we now call the Zika virus.

Aedes aegypti, one vector of Zika virus

The first human case occurred in Nigeria in 1954. It has remained rare and largely innocuous throughout its distribution in Africa and southeast Asia, until 2007 when an epidemic erupted on Yap Island in Micronesia. Subsequent epidemics in the Polynesia, Easter Island, the Cook Islands, and New Caledonia increased concern, but nothing like events in the last two months.

Two concerns have cropped up that have infectious disease specialists alarmed: Zika has jumped the Pacific Ocean and is now found in many countries in South America, Central America, and a few Caribbean nations. It has therefore been classified as a pandemic; there is also evidence the virus may be linked to birth defects, specifically microcephaly. There is also the possibility that the virus can, rarely, trigger Guillain-Barré Syndrome, a type of autoimmune disease.

What we know for certain is that the virus is not contagious. It cannot be spread from one person to another through casual contact. It is transmitted by mosquitoes in the genus Aedes, and possibly by sexual intercourse. Most people who contract the virus exhibit symptoms typical of the flu, and recover quickly.

Cases of the Zika virus in the U.S. are known from Florida, Illinois, Texas, and Hawaii. All victims had returned from travel overseas to countries known to harbor Zika.

This chain of events prompted the Centers for Disease Control to issue a Level 2 Travel Alert for pregnant women on January 15, 2016. Recommendations are that pregnant women avoid traveling to countries where the Zika virus is known to exist. This includes Puerto Rico.

An explosion of 3,500 microcephaly cases in Brazil between October, 2015 and January, 2016 is certainly cause for alarm; and it is at least suspicious that this coincides with the recent infiltration of Zika from the Old World.

Whether mosquito populations in the Gulf Coast states of the U.S. will become carriers of Zika is open to speculation, but considering the other illnesses vectored by mosquitoes, it is always an excellent idea to practice preventive measures such as wearing pants, long sleeves, and hats when outdoors. Repellents with DEET as the active ingredient can be applied per instructions (follow them to the letter). Emptying reservoirs and containers that trap rainwater is also crucial, as these are breeding grounds for mosquitoes.

Sources: Etymologia: Zika virus. Emerg Infect Dis [Internet]. 2014 Jun [date cited]. http://dx.doi.org/10.3201/eid2006.ET2006
"Zika Virus," Wikipedia

Mosquitoes

It’s “Fly Day Friday,” and while not everyone thinks of mosquitoes as flies, that is exactly what they are. Mosquitoes make up the family Culicidae. The majority are aquatic in the egg, larva, and pupa stage of their life cycle. They do not require a great deal of water, or time, to complete their development, and this makes them very difficult to control.

Female Culiseta incidens, the "Cool Weather Mosquito"

The adult female insect, in most species, needs a meal of blood in order to nourish her eggs. Human beings are not usually the host of choice, but we will do in a pinch. Mosquitoes are often cited as the most dangerous of all animals because of their efficiency in delivering disease pathogens to human populations. West Nile Virus may make headlines, but other dangerous mosquito-borne illnesses fly under the radar. Our pets and livestock are also at risk.

The Mosquito Life Cycle

Many mosquitoes breed in treeholes
Female mosquitoes deposit eggs in “rafts,” or singly, on the surface of still water. Larvae, called “wrigglers,” emerge from the eggs and begin their aquatic lives. They breathe through a spiracle at the end of an elongated tube called a “siphon,” at the tip of the abdomen. Most species are filter-feeders that use their mouthparts to strain food particles and/or microorganisms from the water. A few species are predators of other mosquito larvae.

Larvae grow by molting, shedding their flexible yet constraining exoskeleton periodically. Eventually, they molt into the pupa stage, known as a “tumbler.” The pupa is not inert, but quite active, able to dive when danger threatens by thrashing its abdomen. Tumblers breathe through paired siphons (“trumpets”) on its “shoulders.”

Mosquito Life Cycle, © Eric R. Eaton

The adult mosquito pops out of the top of the pupa, and sits on the water surface while its new, winged body hardens and pigments become evident. Adult mosquitoes are covered in scales that may serve to attract mates, but also allow the insects to skip off spider webs, shedding scales instead of becoming entangled.

Mosquito Diversity
There are 176 species of mosquitoes currently recognized in North America. This includes species introduced from other parts of the world through commerce. A new species, Anopheles grabhamii, was described from the Florida Keys in 2002, so there is certainly potential for future additions to our mosquito fauna through several avenues. Only female mosquitoes bite, and not all species bite mammals. Many feed only on birds, a few on amphibians. Some species don’t bite at all.

Male Culex mosquito

Male Mosquitoes
Male mosquitoes are often easily identified by their plumose (feathery) antennae, which they use in part to find females of the same species. They also frequently have enlarged, brush-like palps, paired appendages that are part of their mouthparts. The palps might be mistaken for antennae themselves. Both male and female mosquitoes fuel their flight muscles with flower nectar which they sip through that needle-like proboscis.

Asian Tiger Mosquito

Asian Tiger Mosquito
One prominent example of an exotic species is the Asian Tiger Mosquito, Aedes albopictus. It was first documented in Texas in 1985. One year later it turned up in Florida, among tires imported from overseas for re-treading. This is probably how it spread, as this is one of the “container-breeding” mosquitoes that needs little water to complete its life cycle. Rainwater collects in discarded tires exposed to the elements, and mosquitoes in general are adept at finding such resources. The Asian Tiger Mosquito is now found over much of the eastern U.S. An outbreak in Los Angeles, California in 2001 was traced to a shipment of “lucky bamboo” from China. The insects were eradicated, but subsequent introductions may not have been so successfully suppressed.

Mosquito vs. Mosquito
Aedes albopictus has largely replaced the Yellow Fever Mosquito, Aedes aegypti here in the U.S. Larvae of the Asian Tiger Mosquito compete better for food, and parasites brought with the Asian Tiger Mosquito have had an adverse impact on A. aegypti. Sterility of offspring from interspecific matings has also affected the Yellow Fever mosquito disproportionally. Today, Aedes aegypti is limited to the southeast U.S., a few isolated areas in New York state, and Arizona.

Yellow Fever Mosquito

Disease Transmission
The success of the Asian Tiger Mosquito is ironically somewhat helpful to us. While A. albopictus is known to be able to transmit over thirty viruses, it is not a very efficient vector. Western and Eastern Equine Encephalitis, St. Louis Encephalitis, LaCrosse Encephalitis, and dengue fever are all serious diseases potentially vectored by the Asian Tiger Mosquito.

Malaria is, thankfully, not currently a problem in North America. This was not always the case. Anopheles quadrimaculatus was the vector of this disease in the U.S. and Canada. Malaria affected most of the United States by 1850. One century later, thanks to improvements in sanitation that reduced breeding spots for mosquitoes, and the widespread use of DDT and other potent pesticides, the disease was largely eradicated.

Female Anopheles mosquito

West Nile Virus is transmitted almost exclusively by mosquitoes in the genus Culex. Birds and horses suffer much more frequently from this disease than people; and there is a vaccination available for equines. The elderly, and those people with compromised immune systems, are most at risk.

Dog Heartworm is also a mosquito-borne disease that occasionally afflicts cats as well. The illness itself is caused by a roundworm that is transmitted by at least sixteen species of mosquito. Risk for Dog Heartworm is greatest along the southern Atlantic and Gulf coasts, and the Mississippi River Valley (Nayar & Rutledge-Connelly, 2012).

The "Gallinipper," Psorophora ciliata, a real giant whose larvae eat other mosquito larvae

Mosquito Control and Prevention
You can do a great deal to reduce your risk of exposure to mosquitoes and the diseases they may carry. Consider taking the following measures and precautions:

• Eliminate standing water on your property by cleaning gutters regularly, storing toys, flowerpots, and other potential rainwater collectors indoors, and draining water wherever else it accumulates.
• Apply insect repellents with DEET as the active ingredient, paying careful attention to the directions on the product.
• Comply with local city and county vector control regulations.
• Maintain swimming pools properly
• Change the water in the birdbath frequently, remembering mosquitoes can complete their life cycle in about a week.
• Sleep under mosquito netting when traveling overseas to locations where malaria, dengue, and yellow fever are still problematic.
• Get your pet checked for, and immunized against, Dog Heartworm.

Mosquitoes have their own pests: this one has mites (red spots)

What good are mosquitoes?
When asked this question, I am sometimes tempted to answer “Ask a Plasmodium (the malaria parasite).” We are naturally anthropocentric in our view of other organisms, especially when we see no direct benefit to us. We do know that mosquito-borne diseases have driven our own evolution. Sickle-cell Disease was an evolutionary response to malaria, the misshapen blood cells being inhospitable to the malaria parasite. What else do we owe to mosquitoes, positive or negative? We have much yet to learn, no doubt. Meanwhile, mosquitoes are a fundamental building block in the food chain, responsible for supporting the enormous diversity of fish, birds, bats, and predatory insects found around the globe. We also don’t know what we might lose with the microbes dependent on mosquitoes for transportation from host to host. The next medical breakthrough might come from studying one of those organisms. Lastly, mosquitoes can be important pollinators of flowers. Both male and female mosquitoes visit blossoms for nectar. Still want to wipe them off the face of the Earth?

Yellow Fever Mosquito sipping nectar

Sources: “Asian Tiger Mosquitoes,” Greater Los Angeles County Vector Control District, 2012.
Rios, Leslie, and James E. Maruniak. 2004. “Asian Tiger Mosquito (EENY-319),” Featured Creatures. University of Florida.
Nayar, Jai K., and C. Roxanne Rutledge-Connelly. 2012. “Mosquito-borne Dog Heartworm Disease,” EDIS. University of Florida.
”Mosquito-borne Diseases,” American Mosquito Control Association, 2011.

Ticks

It is often assumed that entomologists and arachnologists find no kind of arthropod to be revolting; that we never swat a mosquito, and that we vigorously advocate that the public refrain from bringing purposeful harm to any of the six- or eight-legged. Well, we have our limits. While I have a mild fascination with ticks, I don’t tolerate their presence on my body, my pets, or anyone else’s for that matter. There are good reasons to be vigilant when it comes to these parasitic mites, and Lyme Disease is only one. Bites from ticks can result in a variety of illnesses, including “heartland virus,” discovered earlier this year.

Male American Dog Tick

Tick types
North American ticks fall into two basic categories: Hard-bodied ticks, family Ixodidae, and soft-bodied ticks (Argasidae). Soft ticks are encountered infrequently, most species being associated with the burrows and nests of rodents, or with bats. A few are hosted by deer and livestock. Hard ticks are abundant, widespread, and nearly impossible to avoid.

Soft-bodied tick, Arizona

Tick biology
Ticks have a life cycle consisting of four stages: egg, larva, nymph, and adult. Larvae have only six legs, and are often referred to as “seed ticks.” The larva takes one blood meal from a host, then drops off the animal. It molts into an eight-legged nymph in about one week. The nymph locates a host and feeds, drops off, and molts into either another nymphal stage or an adult. Adult ticks are sexually mature specimens, whereas the preceding life stages are not.

"Questing" wood tick, California

Ticks find hosts by a behavior known as “questing.” The tick climbs to the tip of a grassblade, leaf, or other object and perches with front legs outstretched. Special sense organs in the legs detect carbon dioxide breathed out by vertebrate animals. Additional sensory organs hone in on odors and body heat. Ticks usually grab a passing host, but they can quickly crawl 10-15 feet to reach a source of carbon dioxide, such as a grazing deer.

Embedded tick nymph

How ticks attach
Ticks bite with mouthparts that, under high magnification, resemble a Swiss army knife of sawblades. The paired chelicerae (“jaws”) saw into the skin of the host, and later tear into tiny capillaries to get the blood flowing. The central, harpoon-like mouthpart is called the hypostome, and that is the tube the tick uses to inject saliva and anti-coagulants, as well as siphoning the blood of the host. The chelicerae anchor the tick in place, but the tick also secretes a glue-like substance that hardens around the entire apparatus. No wonder ticks are so hard to remove once they lodge themselves into a person or pet.

Engorged female American Dog Tick

Tick feeding and reproduction
The exoskeleton covering the abdomen of a female tick is deceptively thick, leathery, and wrinkled, but capable of unbelievable expansion to accommodate a gut that swells with blood. She may balloon to twenty or fifty times her normal size, and up to 200 times her original weight before feeding. She needs the nourishment to produce her eggs….

And ticks are nothing if not prolific. Mating may take place before or after feeding, and on or off of a host. Females are typically larger than males, and often marked more ornately. The two genders find each other through pheromones, chemical scents emitted into the air. Each mated female lays large masses of eggs, some containing up to 20,000 ova. The eggs may be laid on or off of a host.

Blacklegged Tick, © Karl Hillig via Bugguide.net

Deer Ticks
The tick that most often makes the news is the Blacklegged Tick, Ixodes scapularis (formerly known as I. dammini). This is the “deer tick” that vectors Lyme disease, named for the town of Old Lyme, Connecticut where it was first discovered in 1975. The disease was actually known from Europe as early as 1910, where it went by the name erythema migrans, roughly translated to “migrating red rash.” The organism that causes the disease is a spirochaete bacterium, Borrelia burgdorferi.

I won’t go into the particulars about Lyme disease, as there are plenty of other resources available. Contrary to popular belief, only the adult ticks feed on larger mammals like deer. The larvae and nymphs are hosted by birds and rodents. Increasingly, all host reservoirs are becoming more and more adapted to urban and suburban habitats, increasing human exposure to their pathogens and parasites. The Blacklegged Tick is also a vector of babesiosis; and its bite can cause tick paralysis.

The Western Blacklegged Tick, Ixodes pacificus, is the only other known carrier of Lyme disease. Incidences of the disease in west coast states, Utah, southern Nevada, and northwest Arizona are likely attributable to this tick species.

Heartland virus was discovered earlier this year in northwest Missouri. Initially, two patients were thought to be victims of ehrlichiosis, another tick-borne disease, but the patients failed to respond to treatment. Ticks have not been identified conclusively as the vectors of Heartland virus, merely implicated thus far. Deer ticks are substantially smaller than the next two species discussed here.

Female Lone Star Tick

Male Lone Star Tick

Lone Star Tick
Lyme and Heartland may make headlines, but ticks are responsible for a surprising array of medical problems. I recently visited Missouri with my wife, and we were both plucking ticks off ourselves and each other. The first ones I found were Lone Star Ticks, Amblyomma americanum. Females are easily recognized by the bright yellow or ivory spot on their backs. Males are smaller, with a few pale spots along the margin of the abdomen. This tick is well known as a vector of ehrlichiosis, tularemia, and Southern Tick-associated Rash Illness (STARI). It has also been implicated in the transmission of tick paralysis, and suspected as a vector of Q-fever. White-tailed deer are the principal host of all life stages of the tick, though larvae and nymphs are also found on birds.

Male American Dog Tick

Wood Ticks
The other tick we found was the ubiquitous American Dog Tick, Dermacentor variabilis. We even pulled one off of our dog, who we had left with relatives in Kansas for a short time. Rocky Mountain Spotted Fever and tularemia are carried by this species. Tick paralysis is another malady caused by this species, and it is also a suspected carrier of ehrlichiosis. Larvae and nymphs of the American Dog Tick feed on small rodents, while the adults are hosted mostly by medium-sized mammals.

Ticks and pets
It is important to note that Fido can suffer from Lyme disease, too, and also anaplasmosis, another tick-borne ailment attributed to Blacklegged Ticks. Ask your veterinarian for the best ways to keep your pet from getting ticks.

Inspecting for ticks; and preventing them
Ticks have an uncanny ability to remain undetected until they find a spot to feed. Most people cannot feel a tick crawling on their body. Furthermore, ticks have a nasty habit of attaching in places you can’t readily see yourself: the small of your back, behind your knees, or behind your ears. It is recommended that you ask someone to help inspect you for ticks as soon as possible after an outdoor trek where ticks are likely to be found.

You can try to prevent ticks by wearing a longsleeve shirt, tucked into your pants, and with cuffs that fit tightly around your wrists. Long pants, the cuffs tucked into your boots, will help keep ticks at bay, too. Light-colored clothing is best because ticks are dark and more easily visible on beige or other pale colors. Insect repellants with DEET as the active ingredient have at least some efficacy in protecting you from ticks, but apply them correctly according to label instructions.

Female Lone Star Tick

Sources: Drummond, Roger. 1998. Ticks and what you can do about them (2nd edition). Berkeley: Wilderness Press. 74 pp.
Centers for Disease Control. “Ticks”