Living With Zika Infection

Mosquito Bite

Allergic Reaction To Mosquito Bite Photo:

Virus infection and reproduction in humans involves complex interactions between the virus, cells of the host and the immune system. Virologists refer to cells that virus can enter as “permissive”. Both skin fibroblasts (form connective tissue) and epidermal keratinocytes (95% of skin cells) are highly permissive to the Zika Virus. When a mosquito injects saliva containing Zika Virus under the skin, the Zika can enter these cells and reproduce.

Entry into cells requires an interaction between the viral protein coat and factors present on the host cells. Known interactions occur between Zika Virus and cell proteins DC-SIGN, AXL & Tyro3.  A larger set of cell proteins is potentially involved.  Once inside the cell, a race between Zika Virus replication and host immune response ensues. Viruses can only cause disease if they replicate faster than the host immune response can destroy them. Zika triggers a host immune response indicating that it is detected by human cells.  Variation in immune system response can lead to variation in symptoms experienced.

Skin cells are not the only cells permissive to Zika Virus. Zika is able to cross the placenta of pregnant mothers, infect and kill neural stem cells.*  The neural stem cells replicate to produce brain tissue. If enough stem cells are killed, less brain tissue is produced and the brain will be smaller and result in microcephaly.

Initially, there was a correlation between Zika infection and microcephaly, but the underlying mechanism was obscure. We now have a mechanism by which Zika can cause microcephaly. There may be other effects of Zika virus that can contribute. Scientist are continuing investigations. However, available evidence strongly supports Zika as a cause of microcephaly. Zika is a disease that requires a serious response.

*Jonathan J. Miner, Michael S. Diamond. Understanding How Zika Virus Enters and Infects Neural Target Cells. Cell Stem Cell Volume 18, Issue 5, p559–560, 5 May 2016
DOI: http://dx.doi.org/10.1016/j.stem.2016.04.009

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Living With Mosquito Transmitted Virus

Mosquito

Mosquito

Viruses must pass a number of barriers to be transmitted by a mosquito. First the virus particles must be present in the blood of the reservoir (human or other animal) in sufficient quantity to be acquired by a female mosquito. The blood is first pumped through the mouthparts and esophagus and enters the crop of the mosquito, an internal storage sack that is lined with cuticle. The cuticular lining is relatively impermeable to both nutrients and virus particles. Blood slowly is passed out of the crop into the midgut where most absorption occurs.

If virus survives the digestive enzymes and environment of the gut it faces further barriers to transmission. The first barrier is a peritrophic matrix made of protein plus chitin that surrounds the blood meal. Many viruses and microorganisms will adhere to the membrane and be excreted. An infective virus must pass through the peritrophic matrix and access the cell layer of the midgut that separates the lumen from the hemolymph of the insect. The virus must then find a path through or around the midgut cells. Often that path entails a complex series of interactions with proteins in the cell membranes of the mosquito cells.  If successful, the virus move into the hemolymph.

In the hemolymph, the virus must travel to the salivary glands and cross more cell membranes to enter salivary gland cells. Many successful mosquito transmitted viruses are capable of infecting and reproducing in cells of the mosquito salivary gland. The virus particle must be able to leave the salivary gland cells and enter the mosquito saliva. The successful virus particle must survive a mix of digestive enzymes and be able to interact with cell receptors in way that allow the virus to move from midgut to salivary gland.

Additionally, the virus must be able to replicate in cells of the mosquito. A sufficient number of virus particles must enter the host with the mosquito saliva to have a high enough probability that some will escape the host’s defenses.

Despite the many barriers, sufficient viruses evolve the necessary structure to cause disease and human misery. The complex process of virus navigation through the mosquito is being explored by scientists hoping to find ways to improve the barriers to transmission.

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World Bee Day

Bee Hive Art

Slovenian Bee Hive Art Depicting Anton Janša
Photo: Sl-Ziga

Slovenia has declared May 20, “World Bee Day” to draw attention to the importance of bees in our ecosystems and agro-ecosystems. Why May 20? May 20 is the date of baptism (his birthday was not recorded) of Anton Janša, a pioneer in beekeeping and author of books about bee biology. He lectured in Austria during the 1700s, and was recognized as the leading authority on bees.  Anton Janša specialized in the Carniolan bees and is credited with changing the shape of beehives to rectangular boxes that could be stacked. Anton Janša also recommended placing hive in fields where bees could forage more efficiently rather than located for the convenience of the beekeeper.

Anton Janša started work as an artist, but switched to beekeeping and the study of bees as a career. He used his artistic talents to paint his beehives. Slovenia is known for its “bee hive art”. Traditionally, the boards of the hives were painted as a form of folk art. The practice has mostly discontinued, but some of the boards are preserved in Slovenia museums.

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Living With Allium Leaf Miner

Allium Leaf Miner, Phytomyza gymnostoma is a pest of onions and their relatives such as chives, garlics and leeks. This fly has spread across Europe and invaded Great Britain in 2002. It has spread to Asia. This year, it has been reported in Pennsylvania.

Adult flies lay their eggs at the base of the onion stem. The larvae feed on the leaves making tunnels or “mines” beneath the out layer of the leaf.  As larvae grow, they move down the leaf and can burrow into the onion. The burrowing exposes the interior of the onion to disease that promote rot.

The flies emerge in spring and again in September. Commercial growers will probably be able to control the damage with insecticides, but home graders may find control more difficult. Only gardeners in Pennsylvania are likely to see them this year, but in the next decade gardeners in all of North America are likely to get these invasive pests.

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Zika Update: False Negatives, False Positives

Mosquito Bite

Mosquito Bite

Scientists understand (but the general public does not always understand) that all measurements have uncertainty. A false negative would conclude that you did not have a disease when in fact you did. A false positive would conclude that you had a disease when in truth you did not. Molecular tests to identify viruses have uncertainty. The test for Zika virus is relatively new and is good at detecting Zika virus. However, it is new and we cannot yet know if people who have the virus are always correctly identified. In other words, the rate of false negatives is uncertain; more data is needed. The Zika virus test can also detect related viruses that are not Zika. This gives  false positives.

Agencies responsible for informing the public and the media try to give a simple answer rather than a complicated one. The uncertainty surrounding the number of infections in any disease is typically left out of the communication, because it would confuse the core message: the number of Zika cases. In deciding how to present numbers of cases, does the agency err on the side of false positives or false negatives?

The May 20,2016 Zika numbers from the CDC reflect this quandary. The CDC has decided that best practice would be to report the numbers of all pregnant women who have positive laboratory tests and considers the probability of false positives to be relatively small. Previously, Zika infection was only confirmed for pregnant women who had both reported symptoms consistent with Zika infection and had a positive test. However, Zika can have mild symptoms or some people may be asymptomatic. Relying on laboratory test data only is considered closer to the true number (few false positives), thus the new standard. By the new standard, the number of pregnant women considered to have Zika virus exposure is triple the previous number. The new numbers for the US states plus D.C. are 157 cases. The new numbers for US Territories (mostly Puerto Rico) are 122 cases. These are surely underestimates because not all pregnant women are tested for Zika.

Meanwhile, Congress is marching toward gridlock with competing, mutually unacceptable Zika funding bills in the House and Senate. Unfortunately, the Zika epidemic progresses with no regard to political gridlock.

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Blemishes On the Taj Mahal

Taj Mahal

Taj Mahal
Photo: NDTV

The Taj Mahal in Agra, India is an architectural icon and tourist destination. People are alarmed when its white marble turns green. What causes the green slime? A chain of events that involve insects. The green slime is waste, fly specks left by hordes of mating Chironomid midges of the genus, Goeldichironomous. The midge immatures live in nearby Yamuna River where they feed on algae. The midges excrete chlorophyll in their waste that colors the fly specks green. In the past, midge numbers were small and the small amount of droppings went unnoticed.  The midge hordes with enough droppings to form a noticeable coating is a recent occurrence. The fly populations are much larger than in the past because the river has experienced large algal blooms. The algal blooms create plentiful food and habitat for the midges. The algal blooms are fed by dumping organic waste in the river and providing the algae with abundant fertilizer.

Work is underway to clean the green slime from the white marble. However, the longer term solution is to improve the water quality by reducing the level of pollutants entering the river and its tributaries. Pollution abatement could limit the algal blooms and reduce the swarms of midges to more historical and less damaging levels.

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Living With Zika Quarantines

Mosquito

Mosquito

While the US Congress dithers, the rest of the world is stepping up the fight against Zika virus. Countries vary in their concerns and measures. Some measures are more effective than others. In a world of international travel, the US is not immune from compliance with the laws of other countries.

Italy is concerned about the possibility of importing Zika infected mosquitoes that might spread the virus to their population. Not only are they concerned about infected travelers, they are also concerned that mosquitos carrying Zika might board a plane, fly to Italy and spread the virus. The government of Italy instituted a quarantine requiring all aircraft originating from countries reporting Zika virus to undergo disinsection (aerosol insecticide sprays inside the planes that kill mosquitoes). Almost immediately, Italy modified its quarantine to include aircraft originating from all foreign countries. This applies to military as well as business flights and US Air Force personnel are now spraying all Italy bound aircraft.

Costa Rica is treating aircraft with insecticide upon arrival from Zika infested countries with passengers, luggage, etc. still on board. Russia and China are inspecting aircraft arriving from Zika countries but have np quarantine or disinsection.  Australia and New Zealand had preexisting quarantines and disinsection in place for other insects.  Those are adequate for mosquitoes.

The insecticides used have little affect on people at the concentrations needed to kill mosquitoes and other insects. They can be an inconvenience for travelers.  It is unknown if such measures will be effective, or if they will be discontinued if Zika manages to break quarantine in another way.

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