Bed bugs

 Parasitology | Marian Kinsel | Fort Lewis College

Fig. 1 Bed bug actual size representation. Image courtesy of CDC; Blaine Mathison

What are Bed bugs?

Bed bugs are an infestation caused generally by two parasites, Cimex lectularius and Cimex hemipterus who live their entire life with humans. Bed bugs are a red-brown color, oval-shaped insect that can range in size from 1 millimeter to 7 millimeters in size. Have short antennae, black eyes and structures on their back that resemble wings but are not. Adolescent bed bugs have the same features as an adult beg bug but are smaller and resemble more of a yellow body color. These small insects feed on the blood of their human or animal host, which result in irritation. Bed bugs are considered a public health pest by the Environmental Protection Agency, Centers for Disease Control and Prevention, and United States Department of Agriculture. Currently bed bug infestations and bites are not known to cause or spread disease. Although, infestations should not be taken lightly and should be controlled.

Bed bugs bite their human or animal host and usually feed on them in during their sleep. Individual bed bugs feed on their host for about ten minutes. Larger infestations tend to have a line pattern of bites along an edge of clothing or blanket. Bites are often not felt immediately but can later react to the protein excreted through their saliva. Following the bite, swelling and irritation arise and the bite will be visible. It is difficult to differentiate bed big bites from other bites that could be from mosquitos and other insects. Depending on the person, increased amounts of bed bug bites may be show low or sever reactions. Bed bug infestations need to be found to fully classify the bite as a bed bug bite.

Fig. 2 Life cycle of C. lectularius, a casual agent of bed bugs. Image courtesy of Centers for Disease Control and Prevention

Where are they found?

Bed bugs are present in North and South America, Africa, Asia and Europe. Bed bugs are usually thought to be found in poor areas but are present in all economic classes. Smaller infestations are easier to dispose of than larger infestations, but smaller infestations are harder to locate than larger ones. They are found in the folds of mattresses and sheets and excrete and musty odor. Bed bugs can be thought of to be something else, such as carpet beetles or cockroaches. Carpet beetles are darker than bed bugs, have a smaller set of antennae, and their body shape is rounder. Cockroaches are also a red-brown color and oval-shaped but have long antennae and longer legs than a bed bug. Bed bug infestations are commonly resulted from travel as these insects can be found in motels and hotels, regardless of cleanliness and the price paid for the room/suite. They can be unknowingly be carried on travel items such as luggage, furniture and clothes. Bed bugs are most common in apartment buildings, hotels, dormitories, and areas with increased amounts of different human interaction.

Bed bug control

Since bed bug bites do not lead serious diseases, the best way to treat the infected area is to avoid contact with the area, apply antiseptic lotions and in serious cases; consume an antihistamine. To rid infestations, it is safest to contact a professional. There are currently 300 pesticides that are used for bed bug control, including pyrethrins, pyrethroids, desiccants, biochemicals, pyrroles, neonicotinoids, and insect growth regulators. These pesticides are highly recommended, and some are only recommended to be used by professionals. The easiest way to prevent bed bug infestation is to regularly check new purchases, sleeping areas and to practice general hygiene tactics.

Sources:

1.Centers for Disease Control and Prevention

2.Global Health, Division of Parasitic Diseases

3.United States Environmental Protection Agency

4.Colorado State University Extension

5.New York City Health Department

The CATastrophe that is Toxoplasma gondii

By Claire Nagel

What is it?

            Toxoplasma gondii is a protozoan parasite that causes Toxoplasmosis, a very common parasitic infection distributed all over the world.  Cats and other felines are its definitive host, meaning the parasite reaches sexual maturity and reproduces in the feline.  Rodents and other animals are intermediate hosts, while humans are a secondary host.  It can be transmitted through vertical transmission, fecal-oral transmission, iatrogenic transmission (medical procedures), and trophic transmission.  Toxoplasmosis mostly occurs in immunocompromised individuals, such as those infected with AIDS, or children who got it from their mothers.  Symptoms include fever, fatigue, muscle pain, headache, and sore throat, and can result in encephalitis and/or ocular disease.  It can even cause sudden abortions in sheep.   T. gondii is found globally in most continents, including North America, Europe, and South America.  It is estimated that in the United States and United Kingdom, 16-40% of the population are infected, while in Central and South America and Continental Europe, estimations range from 50-80%.

Clinical History

            T. gondii was first discovered accidently in 1908 by Charles Nicolle, a scientist who was working on the disease Leishmania in the North African rodent, Ctenodactylus gundi.  T. gondii was also identified by Alfonso Splendore at around the same time, but in the rabbit population in Sao Paulo.  It was not until 1948 though that Albert Sabin and Harry Feldman published their discovery on the ‘dye test’, a way to diagnose the infection in humans through the use of serum samples.

How is it Transmitted?

            T. gondii can be transmitted by various routes.  It can be transmitted vertically from mother to baby.  If a woman gets infected while pregnant, the infection can be passed on to the developing fetus.  Diseases of this range from mild to severe.  T. gondii can also be transmitted through fecal-oral transmission by consuming tissue cysts from uncooked or undercooked meat, or from food or water contaminated with oocysts from cat feces.  Trophic transmission occurs when a rodent or bird is eaten by another animal, typically a feline, and iatrogenic transmission can happen during blood transfusions and organ transplants.

Why is it so Special?

            T. gondii is an interesting parasite because it changes the behavior of rodents who are infected.  When a rodent is infected with the parasite, they have a reduced distaste to cat odor.  Uninfected rodents flee when they smell cat urine, but infected rodents are not afraid of the smell and do not run away, increasing the likelihood that they will be eaten by a cat.  Reports show that this attraction to cats can be in part due to the parasite activating the sexual arousal pathways in rats.  It is similar to a male rat smelling a female rat in heat, but he has no idea that what he is actually attracted to is cat urine.

Treatments Available

            There are currently no treatments that completely cure an individual of T. gondii, but there are drugs that are effective at treating it, such as sulfadiazine, pyrimethamine, and spiramycine.  These drugs target the parasite during its tachyzoite stage (rapid multiplication), but have limited effectiveness against the tissue cyst stage of T. gondii.  In most cases, animals and humans who have been infected with Toxoplasmosis develop immunity against the disease in the future.  There are no vaccines currently against the parasite in humans, but there is one vaccine used to prevent the Toxoplasma-induced abortion in sheep.

Conclusion

            Overall, T. gondii is a very weird parasite that has many different effects on their hosts.  It causes flu-like symptoms in humans, abortions in sheep, and an attraction to cat pee in rodents.  Discovered in 1908 in North Africa, T. gondii is now prevalent all over the world.  There currently is no cure to the disease, but with further research, it can be done.

Figure 1. The lifecycle of T. gondii (Hill et al., 2002).

References

Hill D, Dubey JP. Toxoplasma gondii: transmission, diagnosis and prevention. Clinical microbiology and infection: the official publication of the European Society of Clinical Microbiology and Infectious Diseases. 2002;8(10):634-640.

Innes EA. A Brief History and Overview of Toxoplasma gondii. Zoonoses & Public Health. 2010;57(1):1-7. doi:10.1111/j.1863-2378.2009.01276.x.

McConkey GA, Martin HL, Bristow GC, Webster JP. Toxoplasma gondii infection and behaviour - location, location, location?. J Exp Biol. 2013;216(Pt 1):113–119. doi:10.1242/jeb.074153

By Wesley Killinen
What is the Zombie-ant Fungus?

Ophiocordyceps Unilateralis, the zombie-ant fungus, is an entomopathogen, a pathogen that infects arthropods such as insects, mites, and ticks (1).  The fungus is characterized by a stalk, stroma, that grows out of the back of an ant’s head.  The stroma is where spores can be released from the perithecial plate.  The species is highly complex and is able to form not only sexual stages (teleomorphs), but also asexual stages (anamorphs) (2).  The diversity of forms acts as a built-in survival mechanism to ensure the success of the species if the primary form (teleomorphs) fail (2).  Ophiocordyceps are a diverse species that can infect different species of ants.  Of the 29 orders of ants it is believed that Ophiocordyceps  are able to colonize 19 of these orders (3).  This wide diversity of potential hosts increases the fungus’s infectious strategies to ensure successful transmission and fill a specific ecological niche.  The fungus modifies the host behavior so that it increases the likelihood of transmission to other ants.  Transmission is aided when an ant ascends a small plant and bites onto the vegetation and dies (3).  The spores from the fungus can then descend to potential ants below to infect a new host.  The reason that the fungus must attack ants outside of their nest is because of the natural behavioral immunity inside ant colonies that can limit the growth and transmission of fungi (3, 4).  Ants are very social insects and they have hygienic behavior, where they clean each other, that reduces transmission of fungi (4).  The phenomenon of altering host behavior is known as an extended phenotype; a term coined by Dawkins (1982) to describe the relationship between a host and parasite, where the parasite will express the trait in any aspect of host shape or behavior (3).  This allows the fungi to be very diverse and fill different ecological niches wherever they are found.  As far as we know, parasitism is one of the most common modes of feeding traits: herbivore, carnivore, and parasitism; to have evolved with as many as half of Earth’s species being parasites (4).

Where can this parasite be found?

The Zombie-ant fungus is typically found in tropical forest ecosystems where its food source is most plentiful (2).  Ants make up less than 2% of all insect species, but they account for 50% of animal biomass in tropical forests (3).  Although ants can occupy very diverse habitats the fungus prefers a warmer and moister environment, such as a tropical forest.  Because ants are dominant members of their terrestrial biomes, they are the most encountered host species for Ophiocordyceps world-wide (3). 

How is the fungus transmitted between ants?

Transmission between ants is caused when a fungal spore from the air or soil encounters an ant (1).  The hypha drill, on the spore, bores through the ant exoskeleton using the enzymes lipase, chitinase, and protease (1).  Over the next few days, the fungus grows in the body cavity as a free-living yeast cell (2).  The fungus then secretes neural toxins to alter the ant’s behavior.  Not much is known about the process of host manipulation; however, there are speculations, but are not concrete enough to be included in this analysis.  The ant will move away from its colony and climb some vegetation where it will begin its “death grip”.  This is where the ant will die, and the fungus stroma begins to bud from the back of the ant’s head (1).  This process allows the fungus to consume the ant and use its body as protection while it waits for the ideal time to release its spores when ant activity has peaked and potential hosts are in the area (2).  The spores are then released to rain down onto more potential victims to continue the cycle. 

What is special about the Zombie-ant Fungus?

Ophiocordyceps Unilateralis produces secondary metabolites called naphthoquinones which have antibacterial, anticancer/antitumor, antiviral, and antimalarial activities (5, 6).  Research is currently underway into how these fungi repel other secondary infections as it protects its host’s body from scavengers.  Antiviral testing has showed some promise with some of the sub-compounds showing significant antiviral activity for Influenza A and Herpes Simplex Virus (HSV-1) (6).  The hope is to use these compounds to develop an antiviral drug to help fight infections.  Also, one of the compounds showed significant anticancer activity against Lymphoid Leukemia (6).  More research into fungal resistance mechanisms may reveal more possibilities for potential drugs.  The race is on to discover more antibiotics that will affect the developing “super bugs” that are becoming more antibiotic resistant.   

References

1.        Mckenna A. Ophiocordyceps unilateralis: The Zombie Ant Fungus – BIOL421 @UNBC – Insects, Fungi and Society.

2.        Evans HC, Elliot SL, Hughes DP. 2011. Ophiocordyceps unilateralis:  A keystone species for unraveling ecosystem functioning and biodiversity of fungi in tropical forests? . Commun Integr Biol 4:598–602.

3.        Araújo JPM, Evans HC, Kepler R, Hughes DP. 2018. Zombie-ant fungi across continents: 15 new species and new combinations within Ophiocordyceps. I. Myrmecophilous hirsutelloid species. Stud Mycol 90:119–160.

4.        Hughes DP, Libersat F. 2019. Parasite manipulation of host behavior. Curr Biol 29:R45–R47.

5.        Amnuaykanjanasin A, Panchanawaporn S, Chutrakul C, Tanicharoen M. 2011. Genes differentially expressed under naphthoquinone- 2 producing conditions in the entomopathogenic fungus 3 Ophiocordyceps unilateralis. Mol Ecol.

6.        Tandon VK, Singh R V., Yadav DB. 2004. Synthesis and evaluation of novel 1,4-naphthoquinone derivatives as antiviral, antifungal and anticancer agents. Bioorganic Med Chem Lett 14:2901–2904.

TRICHOMONIASIS

Quite the trich!

By Bailey Osmer

Figure 1: Trichomonas Vaginalis under a microscope (1).

What is trichomoniasis?

Trichomonas vaginalis is a silent roommate in the world of parasites. This protozoan parasite causes trichomoniasis or “trich” for short, it’s usually asymptomatic when acquired, although symptoms can occur. Trichomoniasis is the most common sexually transmitted infection in the United States and it does not take much to manage it. T. vaginalis is not a scary thing as it is the most common STI, what is scary is what trich can lead to if left untreated.

Who discovered trich and how?

Alexandre Dooné was the first person to describe the presence of T. vaginalis in vaginal discharge in 1836. The lack of scientific tools made it hard for him to study trich. He was able to get an illustration of the protozoan and observe its movement (5). He tagged the name Trichomonas because of two previously found protozoans that had similar physical structures and movements. Something that he did note was that the protozoan had a flagella to help with moving and could only be found in vaginal mucus.

In a book that he released 10 years later he included a picture of T. vaginalis from a vaginal smear which included pus cells, trichomonas, and epithelial cells in it. Donné was not able to specify what diseases Trichomonas could cause but he was able to let other scientists know that it was always associated with pathologic conditions much like syphilis which was found earlier on and gonorrhea found later down the line. Donné stated in his book where the pus mucus is found it may contribute to uterine cervix diseases later down the line. Kunstle, another researcher, is credited with observing the behavior of trich in the female urinary tract. Because of this we have a better understanding of trichs lifecycle today.

How can you get trichomoniasis?

Trichomoniasis is spread through unprotected sex vaginally. The parasite is passed from person to person when semen or vaginal fluids enter the penis or vagina. There are about 3.7 million people in the United States that have this infection and if you were to add in the people who are asymptomatic, that number might double. In women the vulva, vagina, cervix, or urethra are the most commonly infected part of the body and for men it’s the urethra (3). 

Life Cycle

Figure 2: Life cycle of T. vaginalis- The trophozoite (seen at a bigger size bottom left) lives in the female's genital tract or in the males genitalia. Then the protozoan multiplies by binary fission, where it develops into its infective stage and moves to urethra opening. During sexual intercourse an infected male ejaculates into an uninfected female, she now becomes infected. The protozoan migrates to her genital tract and the cycle restarts.

Signs and symptoms

70% of people do not report symptoms when tested positive for trichomoniasis (3). When there have been reported symptoms there seems to be a trend.

For women:

●     Itching, burning, redness or soreness of the genitals;

●     Discomfort with urination;

●     A change in their vaginal discharge (i.e., thin discharge or increased volume) that can be clear, white, yellowish, or greenish with an unusual fishy smell. (STD fact sheet)

For men:

●     Itching or irritation inside the penis;

●     Burning after urination or ejaculation;

●     Discharge from the penis. (3)

Trich is most commonly mistaken for a urinary tract infection since they have similar symptoms. Oftentimes it takes at least 28 days for trichomoniasis to show up on tests because it needs time to develop in the new host (4).

What can trichomoniasis lead to?

Trichomoniasis is nothing to worry about if it is detected early on but let’s say that you are someone who is asymptomatic, what can this mean for you long term?

“In recent years, T. vaginalis infections have been associated with several adverse outcomes, including pelvic inflammatory disease, premature delivery, low birth weight, and increased susceptibility to HIV infection” (2).

Prevention and treatment

The only way to keep yourself from obtaining any STD’s/STI’s is to not partake in sexual intercourse. Many people tend to not get tested because they see it as being shameful or dirty.  If you choose not to get tested regularly, your safest bet is to wear condoms. Trich is not spread through touch, so hugging, a hand shake, sharing drinks, will not put you at risk of becoming infected. If you do get tested it is recommended that you get tested often since there are infections that do not always come with symptoms.  It is common for people to get reinfected after treatment so continue to get tested and let your sexual partners know to get tested as well.

If you do test positive for trich there are medications that you can take to make it go away.  Metronidazole or tinidazole are antibiotic medications that you can take, they are used to specifically fight protozoan infections (3).

References

1.    *, N. (2018, November 15). Trichomoniasis. Retrieved April 17, 2020, from http://www.clpmag.com/2018/11/routine-nucleic-acid-amplification-testing-trichomoniasis/

2.    Barbara Van Der Pol, James A. Williams, Donald P. Orr, Byron E. Batteiger, J. Dennis Fortenberry, Prevalence, Incidence, Natural History, and Response to Treatment of Trichomonas vaginalis Infection among Adolescent Women, The Journal of Infectious Diseases, Volume 192, Issue 12, 15 December 2005, Pages 2039–2044, https://doi.org/10.1086/498217

3.    “STD Facts - Trichomoniasis.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 27 Feb. 2020, www.cdc.gov/std/trichomonas/stdfact-trichomoniasis.htm.

4.    Ducre, Kristena. “Trichomoniasis Symptoms & Testing in Men and Women.” STD Exposed - Sexual Health Blog, 4 Mar. 2019, www.stdcheck.com/blog/everything-about-trich-and-trichomoniasis-testing.

5.    The Discovery of Trichomonas vaginalis. Acta Cytologica 1998;42:1075-1075. doi: 10.1159/000331985

Helminths and the Hygiene Hypothesis

By Isabelle Guerra

What is it?

The hygiene hypothesis was first introduced in the 1980s by David Strachan. Simply put, the hygiene hypothesis states that early exposure to microorganisms helps contribute to the development of the immune system (Strachan,1989). This hypothesis was an attempt to explain the rising occurrences of autoimmune diseases. An autoimmune condition occurs when immune system activity starts to produce to damage to its own body cells (Fleming, 2013). These diseases include allergies, rheumatoid arthritis, Type 1 Diabetes, and many more. The incidence of autoimmune diseases has been rising and the occurrence of most infectious diseases has declined. Without early exposure to microorganisms it is thought that humans will have a less developed immune response, resulting in the development of inflammatory conditions.

This hypothesis attempts to explain why there is an odd distribution of autoimmune diseases in the world. Many studies include maps displaying a distribution of autoimmune disease that appear to be only in “developed” countries, contrasted with parasite infections in “under-developed” countries. A lot of data supports this explanation, but the mechanisms are unknown.

    

Why is it controversial?

A main pillar of this hypothesis is based on claims that helminth infections have been eradicated in developed countries. Another claim is that allergic diseases are not as prevalent in under-developed countries compared to helminth infections. A study conducted with children in Ecuador found that while 25 percent had at least one documented helminth infection 28 percent had a wheeze, 15 percent had skin test reactivity to an allergen, and 17 percent had eczema (Briggs, 2016). This study attempted to show that while helminth infections were common, so were allergies and allergic conditions.  

Many helminth species have effects on their host that actually promote inflammatory disease. Infection with the helminths Ascaris lumbricoides, Toxoplasma canis, and Toxoplasma cati actually makes patients at a greater risk for developing asthma or Loeffler’s pneumonia. Loeffler’s pneumonia is characterized by white blood cell- rich alveoli and interstitial spaces. White blood cells are indicative of helminth infection.

Therapeutic tapeworms?

The term “helminth” is a broad term used to describe a parasitic worm, fluke, nematode, or tapeworm. Helminths have been a part of human evolution for a very long time. They are able to infect humans successfully through their suppression of immune responses.

     In the human body, Helminths typically trigger an elevated white blood cell count as well as a cellular immune response that favors extracellular parasites (TH2). In an attempt to avoid detection, helminths may secrete proteins that actually favor a TH1 response, which is typically more effective against bacteria and viruses.

     Helminths have been used as a treatment for inflammatory diseases. This is the intentional infection with specific intestinal helminths to try to alleviate some symptoms of diseases (Loker, 2015). Since they typically effect the kind of immune response that is also impacted by an autoimmune condition, they are of great interest for therapeutic applications. The most studied application is the introduction of helminths or their eggs to the human intestinal tract (Zwiernik, 2019). This application has been useful in the treatment of Crohn’s disease. The inflammatory response of Crohn’s disease is due to the immune system attacking the normal biome of the gut. Long term treatment with Trichuris suis led to the patients being at levels of Crohn’s disease activity that would be considered remission.

Summary:

     Autoimmune diseases are on the rise around the world. The Hygiene hypothesis attempts to provide an explanation for this increase by theorizing that less exposure to microorganisms leads to a higher prevalence of autoimmune diseases. This hypothesis has been widely studied, but the underlying mechanisms it is referring to is unclear. It has since been replaced with the “old friends” hypothesis, which is based on the idea that infectious organisms have coevolved with hosts and have genes that are important to the development of the host immune system.

Helminths have coevolved with humans and are adapted to suppressing and modifying our immune response for their survival. This mechanism makes them a valuable potential treatment against autoimmune diseases. Promising clinical studies exist, but there is a large field with room for development.

References:

Briggs, Neima, et al. “The Hygiene Hypothesis and Its Inconvenient Truths about Helminth Infections.” PLoS Neglected Tropical Diseases, Public Library of Science, 15 Sept. 2016.

Fleming, J.O. “Helminth Therapy and Multiple Sclerosis.” International Journal for Parasitology, Pergamon, 5 Jan. 2013,

Loker, Eric S., and Bruce V. Hofkin. Parasitology: a Conceptual Approach. Garland Science, 2015.

Strachan, D P. “Hay Fever, Hygiene, and Household Size.” BMJ (Clinical Research Ed.), U.S. National Library of Medicine, 18 Nov. 1989.

Zwiernik, Jacek et al. “Therapeutic applicability of helminths in autoimmune diseases - literature overview.” Przeglad gastroenterologiczny vol. 14,3 (2019): 168-172. doi:10.5114/pg.2019.88164