Fall Insider 2020: Parasites

CONTENTS Parasites & Pregnancy pg 3

Saltman Quarterly

Cricket Suicide pg 4

Eavesdropping Parasite pg 5

Volume 14 | Fall 2020

COVER ILLUSTRATION BY

CORLY HUANG

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SQ INSIDER

arasite regnancy

G

rab a glass of drinking water. It’s probably perfectly clear, and if you place it under a microscope, it’s highly unlikely you’ll discover any sort of parasitic worm. Unfortunately, for millions of communities across the globe where access to clean water is scarce, the devastating impacts of parasitic infection trickle into each and every stage of life, including pregnancy.

Despite their additional and essential burden of producing and sharing nutrients and antibodies for their baby’s survival, pregnant women are often overlooked in studies regarding the impacts of parasitism on various demographics. However, the few studies which do exist have brought fascinating results: recent evidence has suggested that prenatal parasitic infection can boost fertility, but this attack on the mother’s immune system may result in a compromised fetal immune system.

A study published in Science in 2015 examined the effects of various parasites on lifetime birth average in 986 Bolivian women, where the average was ten children per healthy woman. The researchers found that successive hookworm infections during pregnancy brought the birth average down to seven births per woman, decreasing fertility. A town in Alabama was infected with hookworm as recently as 2017, so Americans may not be as far removed from this issue as we think. In contrast, it was also discovered that roundworm infections during pregnancy were projected to increase fertility, since women infected with roundworms had an average of two more children than healthy women. It turns out that the internal immunological environment caused by roundworm infection is actually similar to one created during pregnancy, leading to an internal state that is more conducive to embryonic implantation in the uterus. In 2018, only 24% of women in the United States who used assisted reproductive technology (such as in vitro fertilization) were able to deliver an infant, so the use of roundworm DNA in fertility treatments may bring promising results for women who have difficulty conceiving.

A POTENTIAL FERTILITY SOLUTION

To determine if parasitic fertility treatments are feasible and ethical, scientists must consider whether prenatal parasitic infection has adverse effects on infant vaccine response. A study published in 2015 did exactly that: researchers examined 450 Kenyan women, of which 79% were afflicted with at least one of the following parasitic diseases: malaria, schistosomiasis, lymphatic filariasis, and intestinal helminths.

It’s important to note that the infections were not left untreated over the course of the study; proper treatment was administered during and after pregnancy. After each birth, the newborns were given standard vaccinations for diphtheria (DT), Hepatitis B (Hep B), Haemophilus influenzae (Hib), and tetanus toxoid (TT). For three years after vaccination, the newborns were tested twice a year on their IgG (Immunoglobulin G) antibody levels, which indicated their ability of the children’s immune systems to respond to vaccines. IgG is the most common type of antibody in the body, and it’s also the only antibody a pregnant mother can transfer to her fetus via the placenta, making it an ideal marker for studying the effects of prenatal conditions on fetal immune response.

The researchers discovered that newborns whose mothers had at least one parasitic infection during pregnancy exhibited no

Editors-in-Chief: Andra Thomas, Salma Sheriff Editor-at-Large: Arya Natarajan Head Production Editor: Julia Cheng UTS Production Editor: Nicole Adamson Production Team: Amber Hauw, Tania Gallardo, Ashley Chu, Zarina Gallardo Online Editor: Anjali Iyangar

written by Sharanya Sriram illustrated by Lu Yue Wang statistical difference in lgG levels against two out of four antigens tested (Hep B and TT) compared to healthy mothers. However, when tested for IgG levels against the remaining two antigens (Hib and DT), antibody levels in children of infected mothers were lower than those in children of healthy mothers. Lower IgG levels against Hib and DT indicate inability to produce normal levels of antibodies, leading to higher susceptibility to infection. Unfortunately, this demonstrates that parasitism during pregnancy does impair the child’s ability to respond to vaccinations, emphasizing the need to prevent parasitic infection during pregnancy.

Before determining whether roundworms can realistically be used in fertility treatments, we’ll need a lot more research into the specific effects of roundworm infection on fetal immune response. If such a drug ever enters a clinical trial phase, would it be ethical to purposely inject parasitic DNA into a woman when the infant may suffer detrimental side effects? As immunologists ask these complex questions, we might witness the development of novel fertility solutions within the next few decades. In any case, the complex effects of parasitic infection on pregnancy is a worthwhile topic of study, suggesting that the tools for improving human life often lie within nature itself.

Research Editors: Nikhil Jampana, Noorhan Amani SQ Features Editor: Ingrid Heumann UTS Features Editor: Shreya Shriram Staff Writers: Sharanya Sriram, Jenny Namkoong, Ananya Prasad

Head Illustrator: Sara Kian Staff Illustrators: Corly Huang, Lu Yue Wang, Hannah Abraham, Svetlana McElwain, Yichen Wang Tech Editors: Juliana Fox, Kaz Nuckowski, Max Gruber, Ishrak Ramzan, Anushka Bajaj, Smriti Variyar, Megha Srivatsa

ILLUSTRATION BY

HANNAH ABRAHAM

HOW

written by illustrated by JENNY NAMKOONG SVETLANA MCELWAIN he night falls and crickets slowly emerge on the outskirts of a lake. They feed on other insects containing parasites that eventually grow to be cricket manipulators. Clouding the crickets’ rationality and inducing them to plunge into water, the parasites behave like mysterious lab inventions from sci-fi movies. Even with technological advancements every day, the thought of a living creature’s actions being controlled seems bizarre.

Nonetheless, within our vicinity, these parasites commonly invade terrestrial arthropods like crickets and cause them to “blindly” scurry to water, dive, and meet death’s gate without hesitation.

Nematomorpha, more commonly known as Gordian or horsehair worms, are deadly parasites. Ranging from white, tan, brown to black colors, the peculiar creatures are found in both saltwater (Nectonematida) and freshwater (Gordiida).

It is fascinating to see these long, thin, worm-like creatures squirm around their hosts’ body cavity until they are fully grown. Starting as small, white larvae, they can grow up to one meter in length by relying heavily on hosts for nutrients.

Nematomorpha initially enter aquatic insects like mayflies who serve as temporary hosts.

Here, the parasites patiently wait for their temporary hosts to be consumed by their main hosts: terrestrial arthropods. There are diverse terrestrial arthropod species, but Nematomorpha most frequently enter crickets, grasshoppers, beetles and other common insects. As temporary hosts bridge Nematomorpha with main hosts, the parasites work their way up the food chain from aquatic insects to terrestrial arthropods. Finally, Nematomorpha burrow out the arthropods, wriggle into water, and fulfill their ultimate goal of reproduction. Nematomorpha must induce crickets to jump into water so their life cycle may be satisfied in an aquatic setting.

While there are rare cases where these terrestrial arthropods survive, most main hosts drown in water and face death.

Nematomorpha begin and conclude their life cycle in aquatic environments. When a female Nematomorpha parasite produces strings of eggs, the eggs soon hatch into larvae and enter temporary hosts. As mentioned before, the temporary hosts are consumed by terrestrial arthropods, which then automatically

also transition Nematomorpha to terrestrial arthropods, their key sites of growth. Nematomorpha develop into long, adult worms until they fill every square centimeter of their host’s body cavity.

Of course, this is only possible because the parasites are flexible and able to bend or curve whenever necessary to fit in the hosts’ compact interior space. At their fully grown state, the parasites have an evolutionary drive to return to water, their only feasible site of reproduction. Controlled by Nematomorpha, crickets leap into water, drown, and remain helpless as these parasites pierce through the crickets’ exoskeleton. Once returned to their aquatic habitat, Nematomorpha mate and lay strings of eggs for the cycle to repeat.

There is no definite explanation regarding how the parasites alter crickets’ cognitive processes. Nonetheless, lab studies suggest that parasitic infections are related to changes in protein quantities.

One such study compares protein and histology alterations that occur within crickets’ brains after Nematomorpha invasions. They discovered minimal protein alterations, and the study suggests these small differences occurred purely from the infection process, not Nematomorpha manipulation. However, the parasites also caused vast alterations in the crickets’ neuron productions, and the study suggests these changes in turn impacted the formation of cricket brain cell networks.

The parasites likely hindered normal central nervous system activity of crickets and caused unsettling, abnormal brain functions for them to dive into water (Thomas et al., 2003).

Overall, the lab reveals cricket behavior is altered by both the parasitic infection process and neural changes caused by Nematomorpha manipulation.

Despite the frightening effects Nematomorpha have on terrestrial arthropods, they have beneficial effects on the energy flows of ecosystems. According to a study from Japan, trout populations increased most rapidly during seasons when Nematomorpha brought arthropods to the aquatic environment. These arthropods became a major food source for the fish, thus boosting the trout populations (Sato et al., 2011). As a result, while Nematomorpha climb up the food chain for host invasions, Nematomorpha themselves also serve as an integral food source in the larger ecological food chain.

Although people may misjudge Nematomorpha as negligible worms due to their hair-like appearance, they carry the most threatening authority over crickets. They twist and turn to fill the hosts’ entire body and pierce through their exoskeleton after drowning them in water. Surprisingly, they are not sci-fi lab inventions but instead living organisms with an evolutionary drive to complete their life cycle. Their hazardous invasions and manipulations fortunately only impact invertebrates—so relax and rest assured!

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illustrated by Yichen W ang

U

THE EAVESDROPPING S A PARASITE wr i tt en b y

Ananya P sad ra

pon hearing the word “parasite,” I am reminded of the extraordinary Korean social satire film of 2019, Parasite.

Although the movie was received with warm reception and praised greatly, parasitic organisms are quite the opposite.

You may imagine parasites as invasive and exploitative microscopic organisms that live beyond the realm of human detection; however, parasites come in all shapes and sizes. One such particularly interesting parasite is the dodder (scientific name: Cuscuta)—the most widespread parasitic plant species in the world!

Dodders are a vine-like genus of parasitic plants with over 200 species.

They are widely distributed throughout the tropical and temperate zones; however, many species have piggybacked on their hosts, entering other regions. The dodders have crossed country and climate lines with the help of humans. These parasites prolifically produce seeds in the soil surrounding their host. When humans relocate the host, the dodders get a free ride to previously unexplored regions.

Dodders begin their life cycle looking akin to a piece of string. In contrast to many autotrophic plant species (plants capable of self-nourishment), dodders are rootless, leafless, and cannot efficiently photosynthesize. Hence, these plants need a host to survive. Dodders are parasitic on a wide range of domestic, wild, and agricultural plant species, so finding a host is rarely difficult. The dodders elongate in a spiral fashion, searching for a host to infiltrate. When it identifies a suitable host, dodders produce haustoria (root-

like tubes) that penetrate the stems of the hosts to draw water and nutrition.

With time, the dodder covers the host plant in a woven cocoon of yellow stems, thriving at the expense of their victim.

The dodders have siphoned nutrients and water, but how do they ensure that their own parasitic plant species lives on to breed future generations? Autotrophic plants can rely on their leaves to sense optimal environmental conditions to initiate flowering, pollination, and reproduction.

Unfortunately, dodders can neither grow leaves, nor do they possess the adequate gene sequences to control their flowering mechanism. This raises the question of how the dodder knows when to flower.

Dodders solve this problem by listening in on their hosts. Dodder cell tissues absorb Flowering Locus T (FT), an air-borne protein produced by their hosts, and use this chemical signal to flower synchronously with their host plant. The FT gene, which codes for the FT protein, plays a highly important role in reproduction; it triggers flowering. In dodders, this gene is a pseudogene (non-functional), so they need a host to know when to flower. A recent study on Australian dodders (Cuscutta australis), published in the Proceedings of the National Academy of Sciences, involved an enclosed experiment in which researchers infested three photoperiod-insensitive species with dodders. Naturally, each dodder cluster synchronized its flowering period with that of its host. Furthermore, when the FT gene in the host plants were disabled, the dodders were unable to flower. The researchers also attached a fluorescent protein to the hosts’

FT protein which was found glowing in dodder tissue prior to their flowering. The overwhelming evidence in this study led scientists to the conclusion that dodders do in fact eavesdrop on their hosts!

Synchronous flowering is a unique behavioral characteristic of dodders. If the dodders flowered too soon, their growth would end prematurely and result in dramatically fewer seeds. Conversely, flowering after their hosts would leave the dodders with less nutrients as the host may have already died.

Dodders are also a great example for the evolution of plant parasitism. Scientists have found significant similarities between the genes that code for haustorium in parasitic plants and roots of autotrophic plants.

Other studies have shown that host plants use dodders as a channel of communication to warn other plants about impeding insect attacks and other threats. Digging deeper into the physiology and ecology of dodders can be an instrumental tool for developing new strategies in agricultural crop optimization and forest conservation. Due to evolution, dodders are now the prime thieving masterminds of the plant world.

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