Category Archives: Parasites

Should we save or should we get rid of parasites?

by Piter Kehoma Boll

Parasites are special types of organisms that live on or inside other lifeforms, slowly feeding on them but usually not killing them, just reducing their fitness to some degree. This is a much more discrete way to survive than killing or biting entire parts off, as predators (both carnivores and herbivores) do. However, different from these creatures, parasites are often regarded as unpleasant and disgusting. Yet parasitism is the most common way to get food in nature.

When I introduced the rhinoceros tick in a recent Friday Fellow, I mentioned the dilemma caused by it. Since the rhinoceros tick is a parasite of rhinoceroses, and rhinoceroses are threatened with extinction, a common practice to improve the reproductive fitness of rhinos is removing their ticks, but this may end up leading the rhinoceros tick to extinction.

This actually happened already with other parasites, such as the louse Coleocephalum californici, which was an exclusive parasite of the California condor Gymnogyps californianus. In order to save the condor, a common practice among veterinarians working with conservationists was to delouse the birds and, as a result, this louse is now extinct. The harm that the louse caused to the condor was so little, though, that its extinction was not at all necessary, being nothing more than a case of negligence and lack of empathy for a small and non-charismatic species.

The California condor louse Coleocephalum californici was extinct during a poorly managed campaign to save the California condor Gymnogyps californianus. Image extracted from https://www.hcn.org/blogs/goat/the-power-and-plight-of-the-parasite

The louse Rallicola (Aptericola) pilgrimi has also vanished forever during the conservation campaigns to save its host, the little spotted kiwi, Apteryx owenii, in another failed work.

The efforts to save the little spotted kiwi, Apteryx owenii, from extinction led to the extinction of its louse. Photo by Judi Lapsley Miller.*
The now extinct Rallicola (Aptericola) pilgrimi. Credits to the Museum of New Zealand.***

Another group of parasites that is facing extinction are fleas. The species Xenopsylla nesiotes was endemic to the Christmas Island together with its host, the Christmas Island rat, Rattus macleari. The introduction of the black rat, Rattus rattus, in the island led to a quick decline in the population of the Christmas Island rat, which went extinct at the beginning of the 20th century and, of course, the flea went extinct with it. The flea Acanthopsylla saphes has likely become extinct as well. It was a parasite of the eastern quoll, Dasyurus viverrinus, in mainland Australia. The eastern quoll today is only found in Tasmania, as the mainland Australia’s population went extinct in the mid-20th century. However, the flea was never found in the Tasmanian populations, so it is likely that it died away in mainland Australia together with the local population of its host.

The Manx shearwater flea Ceratophyllus (Emmareus) fionnus. Photo by Olha Schedrina, Natural History Museum.*

But things have been changing lately and fortunately the view on parasites is improving. A recent assessment was made on the population of another flea, the Manx shearwater flea, Ceratophyllus (Emmareus) fionnus. This flea is host-specific, being found only on the Manx shearwater Puffinus puffinus. Although the Manx shearwater is not at all a threatened species and has many colonies along the North Atlantic coast, the flea is endemic to the Isle of Rùm, a small island off the west coast of Scotland. Due to the small population of its host in this island, the flea has ben evaluated as vulnerable. If the Manx shearwater population in the Island were stable, things would be fine but, as you may have guessed already, things are not fine. Just like it happened in Christmas Island, the black rat was also introduced in the Isle of Rúm and has become a predator of the Manx shearwater, attacking its nests.

The Manx shearwater, Puffinus puffinus, is the sole host of the Manx shearwater flea. Photo by Martin Reith.**

Some ideas have been suggested to protect the flea from extinction. One of them is to eradicate the black rat from the Isle or at least manage its population near the Manx shearwater colonies. Another proposal is to translocate some fleas to another island to create additional populations in other Manx shearwater colonies.

But why bother protecting parasites? Well, there are plenty of reasons. First, they comprise a huge part of the planet’s biodiversity and their loss would have a strong impact on any ecosystem. Second, they are an essential part of their host’s evolutionary history and are, therefore, promoters of diversity by natural selection. Removing the parasites from a host would eventually decrease its genetic variability and let it more vulnerable to other new parasites. Due to their coevolution with the host, parasites are also a valuable source of knowledge about the host’s ecology and evolutionary history, helping us know their population dynamics. We can even find ways to deal with our own parasites by studying the parasites of other species, and parasites are certainly something that humans managed to collect in large numbers while spreading across the globe.

Parasites may be annoying but they are necessary. They may seem to weaken their host at first but, in the long run, what doesn’t kill you makes you stronger.

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References:

Kirst ML (2012) The power and plight of the parasite. High Country News. Available at < https://www.hcn.org/blogs/goat/the-power-and-plight-of-the-parasite >. Access on 3 November 2019.

Kwak ML (2018) Australia’s vanishing fleas (Insecta: Siphonaptera): a case study in methods for the assessment and conservation of threatened flea species. Journal of Insect Conservation 22(3–4): 545–550. doi: 10.1007/s10841-018-0083-7

Kwak ML, Heath ACG, Palma RL (2019) Saving the Manx Shearwater Flea Ceratophyllus (Emmareus) fionnus (Insecta: Siphonaptera): The Road to Developing a Recovery Plan for a Threatened Ectoparasite. Acta Parasitologica. doi: 10.2478/s11686-019-00119-8

Rózsa L, Vas Z (2015) Co-extinct and critically co-endangered species of parasitic lice, and conservation-induced extinction: should lice be reintroduced to their hosts? Oryx 49(1): 107–110. doi: 10.1017/S0030605313000628

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Friday Fellow: Eucalyptus Gall Wasp

by Piter Kehoma Boll

Galls are a common abnormal growth on plant tissues, being similar to animal warts, and can be caused by several different parasites, including viruses, bacteria, fungi, arthropods and sometimes even other plants. Sometimes galls can be harmless but they are often able to affect the plant’s fitness to a degree that harms it.

In several species of eucalyptus, including the river red gum presented here last week, a common agent causing galls is Ophelimus maskelli, known as the eucalyptus gall wasp. As its name suggests, this species is a wasp, more precisely a chalcid wasp, therefore related to several parasitoid wasps and the fig wasps.

An adult female eucalyptus gall wasp. Extracted from https://bicep.net.au/pests/ophelimus-maskelli/

The eucalyptus gall wasp is very small, measuring, as an adult, only about 1 mm in length and having a black body. After mating, the female looks for immature eucalyptus leaves, 15–90 days old, growing in the lower tree canopy because leaves are larger there. A female lays about 100 eggs and has a preference for the area close to the leaf’s petiole. As soon as the eggs are laid, a reaction on the leaf tissues leads to the formation of the galls, with one larva growing inside each gall. In heavily infested trees, the whole leaf can be covered and there may be as much as 36 galls per cm². The larva pupates inside the gall and leaves after reaching the adult stage.

A heavily infested eucalyptus leaf with numerous galls. Credits to NHMLA Community Science Program.**

After the adults emerge, the leaves start to desiccate, especially the heavily infested ones, and die, weakening the tree. As a result, the eucalyptus gall wasp is considered a serious eucalyptus pest and can have devastating effects on eucalyptus plantations.

The eucalyptus gall wasp is native from Australia, since most eucalyptus species come from there, but was accidentally introduced in several other countries together with the eucalyptus trees, especially in the last decades. The galls are easily identified as very small, somehow oval eruptions, not very tall, seen from both the upper and lower sides of the leaf. After the adult emerge, there is a visible hole on the gall and the surroundings start to dry.

Several methods to reduce the infections are used, including pesticides and biological control, especially of other chalcid wasps such as the parasitoid Closterocerus chamaeleon. Considering that this pest is a relatively novel nuisance in a global scale, effective control methods are still being developed.

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More hymenopterans:

Friday Fellow: Bullet Ant (on 27 May 2016)

Friday Fellow: Jataí Bee (on 12 August 2019)

Friday Fellow: Turnip Sawfly (on 17 May 2019)

Friday Fellow: Chinese Banyan Wasp (on 5 July 2019)

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References:

Branco M, Boavida C, Durand N, Franco JC, Mendel Z (2009) Presence of the Eucalyptus gall wasp Ophelimus maskelli and its parasitoid Closterocerus chamaeleon in Portugal: First record, geographic distribution and host preference. Phytoparasitica 37(1): 51–54. doi: 10.1007/s12600-008-0010-7

Burks RA, Mottern JL, Waterworth R, Paine TD (2015) First report of the Eucalyptus gall wasp, Ophelimus maskelli (Hymenoptera: Eulophidae), an invasive pest on Eucalyptus, from the Western Hemisphere. Zootaxa 3926(3): 448–450. doi: 10.11646/zootaxa.3926.3.10

Dhahri S, Ben Jamaa ML, Lo Verde G (2010) First record of Leptocybe invasa and Ophelimus maskelli eucalyptus gall wasps in Tunisia. Tunisian Journal of Plant Protection 5: 231–236.

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Friday Fellow: Rhinoceros Tick

by Piter Kehoma Boll

Parasites exist everywhere and, although most of us see them as hateful creatures, more than half of all known lifeforms live as a parasite at least in part of their life. And there are likely many more yet unknown parasites around there. Today I’m going to talk about one of them, which is found in large portions of Africa.

Its name is Dermacentor rhinocerinus, known as the rhinoceros tick. As its name suggests, it is a tick, therefore a parasitic mite, and its adult stage lives on the skin of the white rhinoceros (Ceratotherium simum) and the critically endangered black rhinoceros (Diceros bicornis).

A male rhinoceros tick attached to the skin of a rhinoceros in South Africa. Credits to iNaturalist user bgwright.**

Male and female rhinoceros ticks are considerably different. In males, the body has a black background with many large orange spots. In females, on the other hand, the abdomen is mainly black with only two round orange spots and the plate on the thorax is orange with two small dark spots. Males and females mate on the surface of rhinoceroses. After mating, the female starts to increase in size while the eggs develop inside her and then drops to the ground, laying the eggs there.

A female rhinoceros tick patiently waiting for a rhinoceros to come close. Photo by Martin Weigand.**

The larvae, as soon as they hatch, start to look for another host, usually a small mammal such as rodents and elephant shrews. They feed on this smaller host until they reach the adult stage, when they drop to the ground and climb on the surrounding vegetation, waiting for a rhinoceros to pass by and then attaching to them.

Conservation efforts to preserve biodiversity are mainly focused on vertebrates, especially mammals and birds. Rhinoceroses, which are an essential host for the rhinoceros tick to survive, are often part of conservation programs and, in order to increase their reproductive success, the practice of removing parasites from their skin is common. This is, however, bad for the rhinoceros ticks. If their host is endangered, they are certainly endangered too, and removing them worsens their condition. Are parasites less important for the planet? Don’t they deserve to live just as any other lifeform? We cannot forget that nature needs more than only what we consider cute.

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More mites and ticks:

Friday Fellow: Giant Red Velvet Mite (on 22 June 2016)

Friday Fellow: Cuban-Laurel-Thrips Mite (on 28 June 2019)

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References:

Horak IG, Fourie LJ, Braack LEO (2005) Small mammals as hosts of immature ixodid ticks. Onderstepoort Journal of Veterinary Research 72:255–261.

Horak IG, Cohen M (2001) Hosts of the immature stages of the rhinoceros tick, Dermacentor rhinocerinus (Acari, Ixodidae). Onderstepoort Journal of Veterinary Research 68:75–77.

Keirans JE (1993) Dermacentor rhinocerinus (Denny 1843) (Acari: Ixodida: Ixodidae): redescription of the male, female and nymph and first description of the larva. Onderstepoort Journal of Veterinary Research 60:59–68.

Mihalca AD, Gherman CM, Cozma V (2011) Coendangered hard ticks: threatened or threatening? Parasites & Vectors 4:71. doi: 10.1186/1756-3305-4-71

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Friday Fellow: Salmon Fluke

by Piter Kehoma Boll

Leia em Português

Everybody knows salmons, especially the Atlantic salmon, Salmo salar, and many of us love to eat this fish species as well. However, I’m not here to talk about the Atlantic salmon itself, but to talk about one of its closes companions and antagonists, the salmon fluke.

Scientifically known as Gyrodactylus salaris, the salmon fluke is a flatworm of the clade Monogenea, a group of ectoparasites that infect mainly fish. As its name suggests, the salmon fluke infects salmons, such as the Atlantic salmon, and closely related species, such as the rainbow trout Onchorhynchus mykiss.

Several salmon flukes on a host. Photo by Tora Bardal. Extracted from https://www.drivaregionen.no/no/Gyrodactylus-salaris/

The salmon fluke was first discovered in 1952 in salmons from a Baltic population that were kept in a Swedish laboratory. Measuring about 0.5 mm in length, the salmon fluke attaches to the skin of the fish and is too small to be seen with the naked eye. The attachment happens using a specialized organ full of tiny hooks, called haptor, located at the posterior end of the body. When feeding, the salmon fluke attaches its mouth to the surface of the fish using special glands in its head and everts its pharynx through the mouth, releasing digestive enzymes on the fish, dissolving its skin, which is then ingested. The wounds caused by the parasite’s feeding activity can lead to secondary infections that can seriously affect the salmon’s health.

Artificially colored SEM micrograph of five specimens of Gyrodactylus salaris. Credits to Jannicke Wiik Nielsen. Extracted from https://www.vetinst.no/nyheter/kan-gyrodactylus-salaris-utryddes-i-drammensregionen

Different from most parasitic flatworms, monogeneans such as the salmon fluke have a single host. During reproduction, the hermanophrodite adults release a ciliated larva called oncomiracidium that infects new fish. A single fluke can originate an entire population because it is able to self fertilize.

During the 1970’s, a massive infection by the salmon fluke occurred in Norway following the introduction of infected salmon strains. This led to a catastrophic decrease in the salmon populations in the country, affecting many rivers. Due to this evident threat to such a commercially important species, several techniques have been developed to control and kill the parasite. The first developed methods included the use of pesticides in the rivers, but those ended up having a negative effect on many species, including the salmons themselves. Currently, newer and less aggressive methods have been used.

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References:

Jansen, P. A., & Bakke, T. A. (1991). Temperature-dependent reproduction and survival of Gyrodactylus salaris Malmberg, 1957 (Platyhelminthes: Monogenea) on Atlantic salmon (Salmo salar L.). Parasitology, 102(01), 105. doi:10.1017/s0031182000060406

Johnsen, B. O., & Jenser, A. J. (1991). The Gyrodactylus story in Norway. Aquaculture, 98(1-3), 289–302. doi:10.1016/0044-8486(91)90393-l

Meinilä, M., Kuusela, J., Ziętara, M. S., & Lumme, J. (2004). Initial steps of speciation by geographic isolation and host switch in salmonid pathogen Gyrodactylus salaris (Monogenea: Gyrodactylidae). International Journal for Parasitology, 34(4), 515–526. doi:10.1016/j.ijpara.2003.12.002

Wikipedia. Gyrodactylus salaris. Available at < https://en.wikipedia.org/wiki/Gyrodactylus_salaris >. Access on December 26, 2018.

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Friday Fellow: Wood Cricket’s Worm

by Piter Kehoma Boll

Last week I introduced the small wood cricket, so I will use it as an oportunity to introduce, today, one of its parasites, the Wood Cricket’s Worm Paragordius tricuspidatus.

800px-paragordius_tricuspidatus

Two individuals of the wood cricket’s worm. Photo by D. Andreas Schmidt-Rhaesa.*

The wood cricket’s worm is a member of the phylum Nematomorpha, commonly known as horsehair worms. The adults are free-living worms that inhabit freshwater bodies, especially rivers and streams and have a peculiar mating behavior in which many worms are “tied” to each other in a large knot, like a worm orgy. After mating is finished, the female lays its eggs at the edge of the water, on the ground, where they may eventually be ingested by wood crickets living nearby.

Inside the cricket, the egg hatches and the larvae starts to develop inside the cricket’s body cavity, filling it completely during its development. When the worm is ready to leave its host, it is able to control the host’s behavior, inducing it to jump into a water body, allowing the parasite to leave the cricket and go looking for a partner to mate, starting the cycle again.

Paragordius_tricuspidatus

Paragordius tricuspidatus (arrow) leaving the body of a wood cricket. Photo extracted from Ponton et al. (2006) (See references).

An interesting behavior of the wood cricket’s worm is its ability to escape from the body of a predator. Usually when a wood cricket jumps into the water and the worm is trying to leave the host, an aquatic predator, such as a fish or a frog, may end up eating the cricket, which would put an end to the life of the parasitic worm as well. Recently, however, it has been found that the worm is able to escape the predator’s body, usually through the mouth, when the cricket is eaten. This is the first known case of a parasite escaping a predator of its hosts.

We have to accept that parasitic worms have very adventurous lives.

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References:

Thomas, F.; Ulitsky, P.; Augier, R.; Dusticier, N.; Samuel, D.; Strambi, C.; Biron, D. G.; Cayre, M. (2003) Biochemical and histological changes in the brain of the cricket Nemobius sylvestris infected by the manipulative parasite Paragordius tricuspidatus (Nematomorpha)International Journal of Parasitology 33: 435–443.

Ponton, F.; Lebarbechon, C.; Lefèvre, T.; Biron, D. G.; Duneau, D.; Hughes, D. P.; Thomas, F. (2006) Parasite survives predation on its hostNature 440: 756.

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Friday Fellow: Common giardia

by Piter Kehoma Boll

Parasites are always a group eager to be featured here, and human parasites have a special place in our hearts… sometimes literally. Today’s species, however, has a special place in our small intestine.

Called Giardia lamblia, sometimes also identified under the outdated synonyms Giardia duodenalis or Giardia intestinalis, our species has not a common name, but as it is the most popular and widespread species of the genus Giardia, I decided to call it simply the common giardia.

The common giardia is a flagellated unicellular organism that affects not only humans but several other mammal species. In the wild, the common giardia exists in the form of an inert cyst that can survive for prolonged periods and under different environmental conditions.

giardia_cyst_wtmt3

A cyst of Giardia lamblia. Credits to Centers for Disease Control and Prevention.

When the cysts are ingested by humans or other mammals, they develop into the active stage, called trophozoite, once they reach the small intestine. The trophozoite is a flagellated cell with two well-developed nuclei that make it look like a smiling face. In this stage, the common giardia reproduced by simple binary fission. For a long time, it was thought that sexual reproduction did not occur at all in this species, but some recent evidence indicate that recombination may occur, although it is not very clear yet how it happens.

800px-giardia_intestinalis_28259_1729

Two trophozoites of the common giardia under the microscope. Credits to Josef Reischig.*

The ventral surface of the trophozoite is concave, forming an adhesive disk that attaches the cell to the wall of the intestine, preventing it to be transported downward the intestinal tract. Although not invading the intestinal cells, the infection of Giardia lamblia usually causes diarrhea and malabsorption. When exposed to biliar secretions, the common giardia may develop into a cyst and is thus eliminated with the feces, allowing the cycle to begin again.

Humans are very often contaminated by several means, such as by ingesting contaminated water, which may include both urban untreated water or clear water in the wild where other mammals may have defecated. It is, therefore, a common infection among hikers, people living under poor sanitary conditions and so on.

The common giardia has some peculiarities, such as the lack of mitochondria, which for some time led to the assumptions that they may belong to a very primitive group of Eukaryotes. Recently, however, a vestigial organelle that likely derived from mitochondria, named mitosome, has been found in this species, suggesting that this feature is a secondary loss caused by its parasitic life in an anoxic environment.

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References:

Adam, R. D. (2001) Biology of Giardia lambliaClinical Microbiology Reviews 14(3): 447–475.

Wikipedia. Giardia lamblia. Available at < https://en.wikipedia.org/wiki/Giardia_lamblia >. Access on 28 June 2018.

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Friday Fellow: Pear Rust

by Piter Kehoma Boll

Beautiful and deadly, today’s fellow appears during spring as gelatinous orange projections coming out of juniper trees in Europe and North America. Its name is Gymnosporangium sabinae, commonly known as the pear rust.

800px-gymnosprangium_rust_on_a_juniper_tree

The jelly-like horns of the pear rust on a juniper tree. Photo by Mark Sadowski.*

The pear rust is a basidiomycete, i.e., a fungus of the phylum Basidiomycota, therefore related to the common mushrooms, but belonging to a different class, the Puccioniomycetes.

During winter, the pear rust remains in a resting state inside branches and twigs of juniper trees. After wet days in spring, the fungus sprouts and appears as horn-like growths covered by an orange gelatinous mass, which are called telia. The telia produce wind borne spores called teliospores that can infect pear trees.

668px-birnengitterrost_baum

The pear rust on pear leaves. Photo by Jan Homann.

Once reaching the pear tree, the teliospores germinate and infect the leaves of the new host. The infection appears in summer as rust-colored spots on the leaves, hence the name pear rust. In heavily infected plants, the effects of the pear rust can be severe, sometimes causing the plant to lose all its leaves.

In pear trees, the fungus produce reproductive structures known as aecia. They come out from the underside of pear leaves and produce spores called aeciospores, which are able to infect new juniper trees.

800px-birnengitterrost_gymnosporangium_fuscum

The aecia coming out of the rust on a pear tree. Photo by H. Krisp.**

Due to the economic importance of pear trees to humans, the pear rust is a species of great concern. Some countries have policies intended to reduce the spread of the disease, such as preventing transportation of juniper trees from areas known to have the fungus to areas in which it is unknow. In areas where the fungus exist, the solutions to reduce the damage include the use of chemical fungicides, the removal of infected branches in juniper trees and sometimes the removal of any juniper tree around the areas where pear trees are cultivated.

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References:

Fraiture, A.; Vanderweyen, A. (2011) Gymnosporangium sabinae: such a beautifiul disease. Scripta Botanica Belgica 11: 193–194.

Ormrod, D. J.; O’Reilly, H. J.; van der Kamp, B. J,; Borno, C. (1984) Epidemiology, cultivar susceptibility, and chemical control of Gymnosporangium fuscum in British Columbia. Canadian Journal of Plant Pahology6: 63–70.

Wikipedia. Gymnosporangium sabinae. Available at < https://en.wikipedia.org/wiki/Gymnosporangium_sabinae >. Access on April 27, 2018.

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