Unit 6: Parasitic Helminths - Biology

Unit 6: Parasitic Helminths - Biology

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Unit 6: Parasitic Helminths

Helminth secretomes reflect different lifestyles and parasitized hosts

Helminths cause a number of medical and agricultural problems and are a major cause of parasitic infections in humans, animals and plants. Comparative analysis of helminth genes and genomes are important to understand the genomic biodiversity and evolution of parasites and their hosts in terms of different selective pressures in their habitats. The interactions between the infective organisms and their hosts are mediated in large part by secreted proteins, known collectively as the "secretome". Proteins secreted by parasites are able to modify a host's environment and modulate their immune system. The composition and function of this set of proteins varies depending on the ecology, lifestyle and environment of an organism. The present study aimed to predict, in silico, the secretome in 44 helminth species including Nematoda (31 species) and Platyhelminthes (13 species) and, understand the diversity and evolution of secretomes. Secretomes from plant helminths range from 7.6% (943 proteins) to 13.9% (2,077 proteins) of the filtered proteome with an average of 10.2% (1,412 proteins) and from free-living helminths range from 4.4% (870 proteins) to 13% (3,121 proteins) with an average of 9.8% (2,126 proteins), respectively, and thus are considerably larger secretomes in relation to animal helminth secretomes which range from 4.2% (431 proteins) to 11.8% (2,419 proteins) of the proteomes, with an average of 7.1% (804 proteins). Across 44 secretomes in different helminth species, we found five conserved domains: (i) PF00014 (Kunitz/Bovine pancreatic trypsin inhibitor domain), (ii) PF00046 (Homeobox domain), (iii) PF00188 (cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins), (iv) PF00085 (Thioredoxin) and (v) PF07679 (Immunoglobulin I-set domain). Our results detected secreted proteins associated with invasion, infection, adhesion and immunoregulation processes as protease inhibitors and cytokines, among other functions. In summary, this study will contribute towards the understanding of host-parasite interactions and possibly identify new molecular targets for the treatment or diagnosis of helminthiases.

Keywords: Biodiversity Computational biology Helminths Host-parasite interaction Protein evolution Secretome.

Copyright © 2017 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.

Hepatitis C and Helminthic Infections

Khalifa S. Khalifa , Othman Amin , in Hepatitis C in Developing Countries , 2018


Helminthic infections occur worldwide, especially in developing countries. About one-quarter of the world's population, i.e., 1.5 billion, are infected with one or more of the major soil-transmitted helminths, including hookworms, ascarids, and whipworms. Schistosomes infect more than 200 million people worldwide with 600 million at risk in 74 countries. The interaction between helminths and the host's immune system provokes particular immunomodulatory and immunoregulatory mechanisms that ensure their survival in the host for years. However, these changes might impair the immunologic response to bystander bacterial, viral, and protozoal pathogens and to vaccination. Modulation of the immune system by infection with helminthic parasites is proposed to reduce the levels of allergic responses and to protect against inflammatory bowel disease. In this section, we summarize the immunologic milieu associated with helminthic infections and its impact on hepatitis C virus, and HIV in humans and experimental animals.

Host Immunity and Inflammation to Pulmonary Helminth Infections

Helminths, including nematodes, cestodes and trematodes, are complex parasitic organisms that infect at least one billion people globally living in extreme poverty. Helminthic infections are associated with severe morbidity particularly in young children who often harbor the highest burden of disease. While each helminth species completes a distinct life cycle within the host, several helminths incite significant lung disease. This impact on the lungs occurs either directly from larval migration and host immune activation or indirectly from a systemic inflammatory immune response. The impact of helminths on the pulmonary immune response involves a sophisticated orchestration and activation of the host innate and adaptive immune cells. The consequences of activating pulmonary host immune responses are variable with several helminthic infections leading to severe, pulmonary compromise while others providing immune tolerance and protection against the development of pulmonary diseases. Further delineation of the convoluted interface between helminth infection and the pulmonary host immune responses is critical to the development of novel therapeutics that are critically needed to prevent the significant global morbidity caused by these parasites.

Keywords: Ascaris Schistosoma hookworm host immune response inflammation lung pathologies.

Copyright © 2020 Weatherhead, Gazzinelli-Guimaraes, Knight, Fujiwara, Hotez, Bottazzi and Corry.


Helminth-induced pathogenesis of human pulmonary…

Helminth-induced pathogenesis of human pulmonary disease. Helminth infections can cause pulmonary pathology due…

Activated innate and adaptive immune…

Activated innate and adaptive immune pathways in the lungs during helminth infection. Innate…


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Eukaryotic Microbes - Lab 10

 A model organism is used in microbiology, molecular biology, and biochemistry labs for analysis and research. Saccharomyces cerevisiae is often used as one because its smaller in size, has a fast growth rate, low costs, safe and easy to work with. It is important for the role of yeast in many foods and drinks, such as breads, wine, and beer.

  1. Research and discuss the properties of mold that make them sometimes beneficial to humans, and sometimes potentially harmful.

 Mold can be both beneficial to humans and sometimes potentially harmful. The benefits from mold is the citric acid that is used in medications, such as ones that can be applied to the nervous system, help with drug testing, and cancers. The potential harms can be from aspergillus and inhaled by humans and animals which can cause serious infections and produce toxins.

  1. Parasitic helminths are a major cause of disease in undeveloped countries around the world. Discuss the role that microbiologists can and have played in helping to reduce the number of infections caused by parasitic helminths as well as diagnoses and treatments.

 Microbiologists can and have played a helping part to reduce the number of infections caused by parasitic helminths as well as diagnoses and treatments because they have studied the different vehicles/hosts/vectors. They have identified

the characteristics of the diagnosis and how to prevent the transmission from better hygiene, vaccines, as well as proper cleaning of drinking water.

 Based on my results the more acidic and bright conditions were the most favorable for mold growth on both the bread and the apple.

 No, these conditions would not apply to all fungal growth.

  1. Did you notice a difference in mold growth on the bread vs the apple? If so, what do you think might account for this difference?

 There was more growth on the apple vs the bread. I think this has to due to the fact that the apple has more moisture, natural/raw sugar and wasn’t processed like the bread, which provided a better environment and nutrient for the microbial growth.

  1. How would changing the type of bread (e.g. fresh from a bakery, no preservatives vs. prepackaged with preservatives) affect the results?

 Changing the type of bread used to fresh baked with no preservatives vs the prepacked with preservatives would have increased the growth rate and abundance of bacteria more rapidly. The preservatives keep it from spoiling/growing mold as fast.

  1. How do you think changing the temperature at which the bags were incubated affected the results?

 Changing the temperature at which the bags were incubated could greatly affect the results. When the bread is at a neutral temperature the microbial growth will be more steady, if you increase the temperature it may growth more rapidly, but if you increase it too much it may kill the bacteria, and if you lower the temperatures too much it may preserve the bread more and slow the growth rate.

 I would test these predictions/hypotheses with different types of bread (fresh baked and prepackaged) at different temperatures and environments.

  1. Look up the pH of lemon juice and vinegar. Based on your results and your knowledge of favorable environmental conditions for fungal growth, what can you conclude about the effect of pH on growth?

 Lemon juice is around a 2.0 pH while vinegar is about a 2.5 pH. This making the lemon juice more acidic and producing more growth.

 Penicillium is the source of the mold that grew on the samples. This mold came from both the environment and airborne from the beginning of the experiment.

Learning Outcomes

Upon successful completion, students will have the knowledge and skills to:

On satisfying the requirements of this course, students will have the knowledge and skills to:

  1. Identify, describe and contrast unicellular parasites and parasitic worms
  2. Describe particular human and non-human parasitic diseases
  3. Prepare and observe live parasitic specimens and test students' own seropositivity for a particular parasitic infection
  4. Report on observations of biological specimens such as parasites
  5. Appraise the impacts of parasitic diseases on human societies
  6. Evaluate the complexity of the parasite/host relationship (parasite evasion mechanisms vs host defensive mechanisms)
  7. Independently research current subjects in parasitology using published books and original papers.

Population Biology of Parasitic Nematodes: Applications of Genetic Markers

This chapter describes genetic approaches to answer a variety of questions in the population biology of parasitic helminths. It lays particular emphasis on nematode parasites. The chapter describes levels of heterozygosity revealed by allozymes and patterns of variation in a variety of different sequence types. It illustrates the ways this variation is distributed in parasite populations, and the ways these patterns can be used to ask questions about the various aspects of nematode biology and epidemiology. It also discusses the interspecific level and describes the way genetic approaches have clarified ideas on nematode speciation and revealed a wealth of sibling species. The chapter presents examples of the use of markers for clarifying life cycles and deals with genes responsible for drug resistance. It also discusses other miscellaneous uses of genetic markers. Much of this section is speculative and describes fields in which genetic markers should see a greater usage in the future.

About Parasites

A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host. There are three main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites.

Entamoeba histolytica is a protozoan. A microscope is necessary to view this parasite. Credit: CDC.

Protozoa are microscopic, one-celled organisms that can be free-living or parasitic in nature. They are able to multiply in humans, which contributes to their survival and also permits serious infections to develop from just a single organism. Transmission of protozoa that live in a human&rsquos intestine to another human typically occurs through a fecal-oral route (for example, contaminated food or water or person-to-person contact). Protozoa that live in the blood or tissue of humans are transmitted to other humans by an arthropod vector (for example, through the bite of a mosquito or sand fly).

The protozoa that are infectious to humans can be classified into four groups based on their mode of movement:

  • Sarcodina &ndash the ameba, e.g., Entamoeba
  • Mastigophora &ndash the flagellates, e.g., Giardia, Leishmania
  • Ciliophora &ndash the ciliates, e.g., Balantidium
  • Sporozoa &ndash organisms whose adult stage is not motile e.g., Plasmodium, Cryptosporidium

An adult Ascaris lumbriocoides worm. They can range from 15 to 35 cm.
Credit: CDC.

Helminths are large, multicellular organisms that are generally visible to the naked eye in their adult stages. Like protozoa, helminths can be either free-living or parasitic in nature. In their adult form, helminths cannot multiply in humans. There are three main groups of helminths (derived from the Greek word for worms) that are human parasites:

  • Flatworms (platyhelminths) &ndash these include the trematodes (flukes) and cestodes (tapeworms).
  • Thorny-headed worms (acanthocephalins) &ndash the adult forms of these worms reside in the gastrointestinal tract. The acanthocephala are thought to be intermediate between the cestodes and nematodes.
  • Roundworms (nematodes) &ndash the adult forms of these worms can reside in the gastrointestinal tract, blood, lymphatic system or subcutaneous tissues. Alternatively, the immature (larval) states can cause disease through their infection of various body tissues. Some consider the helminths to also include the segmented worms (annelids)&mdashthe only ones important medically are the leeches. Of note, these organisms are not typically considered parasites.

An adult louse. Acutal size is about as big as a sesame seed.
Credit: CDC.

Although the term ectoparasites can broadly include blood-sucking arthropods such as mosquitoes (because they are dependent on a blood meal from a human host for their survival), this term is generally used more narrowly to refer to organisms such as ticks, fleas, lice, and mites that attach or burrow into the skin and remain there for relatively long periods of time (e.g., weeks to months). Arthropods are important in causing diseases in their own right, but are even more important as vectors, or transmitters, of many different pathogens that in turn cause tremendous morbidity and mortality from the diseases they cause.

Parasitic infections cause a tremendous burden of disease in both the tropics and subtropics as well as in more temperate climates. Of all parasitic diseases, malaria causes the most deaths globally. Malaria kills more than 400,000 people each year, most of them young children in sub-Saharan Africa.

The Neglected Tropical Diseases (NTDs), which have suffered from a lack of attention by the public health community, include parasitic diseases such as lymphatic filariasis, onchocerciasis, and Guinea worm disease. The NTDs affect more than 1 billion people worldwide, largely in rural areas of low-income countries. These diseases extract a large toll on endemic populations, including lost ability to attend school or work, stunting of growth in children, impairment of cognitive skills and development in young children, and the serious economic burden placed on entire countries.

However, parasitic infections also affect persons living in developed countries, including the United States.

Roundworms (Nematodes)

Figure 86-5 shows the structure of nematodes. In contrast to platyhelminths, nematodes are cylindrical rather than flattened hence the common name roundworm. The body wall is composed of an outer cuticle that has a noncellular, chemically complex structure, a thin hypodermis, and musculature. The cuticle in some species has longitudinal ridges called alae. The bursa, a flaplike extension of the cuticle on the posterior end of some species of male nematodes, is used to grasp the female during copulation.

Figure 86-5

Structure of nematodes. (A) Female. (B) Male. Transverse sections through the midregion of the female worm (C) and through the esophageal region (D). (Modified from Lee DL: The Physiology of Nematodes. Oliver and Boyd, Edinburgh, 1965, with permission.) (more. )

The cellular hypodermis bulges into the body cavity or pseudocoelom to form four longitudinal cords𠅊 dorsal, a ventral, and two lateral cords—which may be seen on the surface as lateral lines. Nuclei of the hypodermis are located in the region of the cords. The somatic musculature lying beneath the hypodermis is a single layer of smooth muscle cells. When viewed in cross-section, this layer can be seen to be separated into four zones by the hypodermal cords. The musculature is innervated by extensions of muscle cells to nerve trunks running anteriorly and posteriorly from ganglion cells that ring the midportion of the esophagus.

The space between the muscle layer and viscera is the pseudocoelom, which lacks a mesothelium lining. This cavity contains fluid and two to six fixed cells (celomocytes) which are usually associated with the longitudinal cords. The function of these cells is unknown.

The alimentary canal of roundworms is complete, with both mouth and anus. The mouth is surrounded by lips bearing sensory papillae (bristles). The esophagus, a conspicuous feature of nematodes, is a muscular structure that pumps food into the intestine it differs in shape in different species.

The intestine is a tubular structure composed of a single layer of columnar cells possessing prominent microvilli on their luminal surface.

The excretory system of some nematodes consists of an excretory gland and a pore located ventrally in the mid-esophageal region. In other nematodes this structure is drawn into extensions that give rise to the more complex tubular excretory system, which is usually H-shaped, with two anterior limbs and two posterior limbs located in the lateral cords. The gland cells and tubes are thought to serve as absorptive bodies, collecting wastes from the pseudocoelom, and to function in osmoregulation.

Nematodes are usually bisexual. Males are usually smaller than females, have a curved posterior end, and possess (in some species) copulatory structures, such as spicules (usually two), a bursa, or both. The males have one or (in a few cases) two testes, which lie at the free end of a convoluted or recurved tube leading into a seminal vesicle and eventually into the cloaca.

The female system is tubular also, and usually is made up of reflexed ovaries. Each ovary is continuous, with an oviduct and tubular uterus. The uteri join to form the vagina, which in turn opens to the exterior through the vulva.

Copulation between a female and a male nematode is necessary for fertilization except in the genus Strongyloides, in which parthenogenetic development occurs (i.e., the development of an unfertilized egg into a new individual). Some evidence indicates that sex attractants (pheromones) play a role in heterosexual mating. During copulation, sperm is transferred into the vulva of the female. The sperm enters the ovum and a fertilization membrane is secreted by the zygote. This membrane gradually thickens to form the chitinous shell. A second membrane, below the shell, makes the egg impervious to essentially all substances except carbon dioxide and oxygen. In some species, a third proteinaceous membrane is secreted as the egg passes down the uterus by the uterine wall and is deposited outside the shell. Most nematodes that are parasitic in humans lay eggs that, when voided, contain either an uncleaved zygote, a group of blastomeres, or a completely formed larva. Some nematodes, such as the filariae and Trichinella spiralis, produce larvae that are deposited in host tissues.

The developmental process in nematodes involves egg, larval, and adult stages. Each of four larval stages is followed by a molt in which the cuticle is shed. The larvae are called second-stage larvae after the first molt, and so on (Fig. 86-6). The nematode formed at the fifth stage is the adult. Figure 86-7 summarizes the life cycles of several intestinal nematodes.

Figure 86-6

Stages in the development of nematodes. (Adapted from Lee DL: The Physiology of Nemotodes. Oliver and Boyd, Edinburgh, 1965, with permission.)

Watch the video: Helminths: Cestodes and Trematodes transmission, clinical importance, and treatment (February 2023).