Monthly Archives: December 2020

by Piter Keo | December 25, 2020 · 8:00 am

Friday Fellow: Christmas Rose

by Piter Kehoma Boll

There is a plant in Europe that flowers in winter when the ground is covered by snow. In the warmer regions of southern Europe, it flowers around Christmas and, because of that, it is commonly known as Christmas Rose. Its scientific name is Helleborus niger and it is not actually a rose, but a buttercup.

The Christmas rose is a small evergreen plant, reaching only a few centimeters in height and have dark leathery leaves. Their roots are black, which is the reason why its specific epithet is niger and other of its common names is black hellebore. During winter and early spring, it produces considerably large flowers with five white petals which may have a pink or green tinge. The center of the flower has a large mass os yellow stamens with a small group of white or yellow pistils coming out of them in the middle.

The beautiful flower of the Christmas rose. Photographed in Italy by Roberto Ghiglia.*

Due to the fact that it flowers in winter, which is not very common, the Christmas Rose is a popular garden flower in Europe. It is, however, quite difficult to grow well because it does not tolerate acid and dry soil or full sun. There are some cultivars with larger flowers, pink flowers or double flowers.

The general aspect of the plant without flowers. Photo by Tiia Monto.**

The Christmas rose has many toxic compounds just like other closely-related plants such as buttercups and poppies. It has been used historically to treat several conditions, such as insanity, melancholy and epilepsy, and also as a purgative. There are also many “magic” properties associated with the plant, including the ability to drive out evil influences or turn witches invisible. In large quantities the plant can cause death and there are even some sources that suggest that it was used to assassinate Alexander the Great.

A few clinical studies with Christmas Rose extracts suggest that this plant may have immunostimulant and antitumor properties, which could lead to the development of new anticancer drugs. However, the main interest on this plant today is still related to its ornamental use.

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References:

Büssing, A., & Schweizer, K. (1998). Effects of a phytopreparation from Helleborus niger on immunocompetent cells in vitro. Journal of ethnopharmacology, 59(3), 139-146.

Schink, M., Garcia-Käufer, M., Bertrams, J., Duckstein, S. M., Müller, M. B., Huber, R., … & Gründemann, C. (2015). Differential cytotoxic properties of Helleborus niger L. on tumour and immunocompetent cells. Journal of ethnopharmacology, 159, 129-136.

Werthmann, P. G., Saltzwedel, G., & Kienle, G. S. (2017). Minor regression and long-time survival (56 months) in a patient with malignant pleural mesothelioma under Viscum album and Helleborus niger extracts—a case report. Journal of thoracic disease, 9(12), E1064.

Wikipedia. Helleborus niger. Available at < https://en.wikipedia.org/wiki/Helleborus_niger >. Access on 24 December 2020.

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** This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Friday Fellow: Black-Fly Nematode

by Piter Kehoma Boll

During the past two weeks I presented the annoying damaging black fly and the terrible river-blindness worm, which is transmitted by the blackfly and cause river blindness in humans. We saw that it is difficult to control the spread of the worm and the reproduction of the black fly due to a series of economic and ecological factors. There is, however, another strategy that has been investigated: the use of another worm.

While the river blindness worm infects adult black flies and does not prevent their reproduction, another worm, Isomermis lairdi, which I will call the black-fly nematode, has a quite different relationship with black flies.

As the name black-fly nematode implies, this worm is a nematode (roundworm) just like the river-blindness worm, but it belongs to a different nematode group. One of its close relatives was presented here as a past Friday Fellow, the grasshopper nematode.

Adults of the black-fly nematode are not parasites. They live as free organisms in the water near the bottom of rivers. After mating, females lay their eggs in the sand of the river bottom, attaching them with an adhesive substance, and die soon after, while males can survive for months. In regions where the river has a dry period, the eggs remain dormant for up to 8 months, hatching only when water starts to flow again. The first moult of the larvae occurs inside the egg and they hatch soon after.

Preserved larvae of the ornate black fly (*Simulium ornatum*) filled with black-fly nematodes (A) and live black fly larva with nematodes inside it (B). Credits to Gradinarov (2014).*

This newborn pre-parasitic larvae are very mobile, moving through the water column, and hope to be ingested by the larvae of black fly, which are there filtering organic particles and organisms from the water. Once inside the black fly, the larvae of the nematode start feeding on the black fly’s tissues, especially their fatty tissue. If the infection occurs during the first instars of the black fly larvae, these are unable to pupate because their fatty tissue becomes completely depleted. Thus, the black fly dies as a larva, consumed by the nematodes. If the larvae are infected during their later instars, they are still able to pupate and develop into adult black flies, but infected adult females are unable to transmit the river blindness worm, even if they get infected by them after biting an infected human. This is so because the river blindness worm needs at least one week inside the black fly to develop into the stage that can infect humans, and females that are infected by the black fly nematode die before that.

The nematodes leave the black fly as a pre-adult stage, have two simultaneous molts about 3 to 4 days after emerging from the host, and become adults ready to mate, which restarts the cycle.

The species known as Isomermis lairdi can infect several black fly species, but it is still not clear whether this is indeed only one nematode species or actually several different ones, each adapted to parasitize a specific black fly species. Studies with other “versatile” nematodes that infect black flies showed that each black fly species is infected by a different nematode lineage, and the same may be true to Isomermis lairdi.

Understanding the life cycle of the black fly nematode and being able to tell whether the same lineage can infect different black fly species or not can help humans create a “mutualistic” association with this worm to fight against the river-blindness worm with a more nature-friendly and probably more effective strategy than the ones used today.

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References:

Crainey, J. L., Wilson, M. D., & Post, R. J. (2009). An 18S ribosomal DNA barcode for the study of Isomermis lairdi, a parasite of the blackfly Simulium damnosum sl. Medical and veterinary entomology, 23(3), 238-244. https://doi.org/10.1111/j.1365-2915.2009.00814.x

Davies, J. B., McMahon, J. E., Beech-Garwood, P., & Abdulai, F. (1984). Does parasitism of Simulium damnosum by Mermithidae reduce the transmission of onchocerciasis?. Transactions of the Royal Society of Tropical Medicine and Hygiene, 78(3), 424-425. https://doi.org/10.1016/0035-9203(84)90156-1

Gradinarov, D. (2014). The mermithid species Isomermis lairdi (Nematoda, Mermithidae), previously only known in Africa, found in Europe. ZooKeys, (454), 1. https://doi.org/10.3897/zookeys.454.7577

Walsh, J. F., & Ocran, M. H. (1985). Mermithid parasitism of Simulium damnosum sl and the transmission of human onchocerciasis. Transactions of the Royal Society of Tropical Medicine and Hygiene, 79(6), 843-844. https://doi.org/10.1016/0035-9203(85)90133-6

World Health Organization. (‎1980)‎. Data sheet on the biological control agent, Isomermis lairdi. World Health Organization. https://apps.who.int/iris/handle/10665/144782

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* This work is licensed under a Creative Commons Attribution 4.0 International License.

Friday Fellow: River-Blindness Worm

by Piter Kehoma Boll

Last week I introduced the not-so-lovely damaging black fly Simulium damnosum, a vector of the worm that causes river blindness in humans. So what better than introducing this very worm today?

Named Onchocerca volvulus, today’s fellow lacks a common name, but since it is the cause of the disease known as onchocerciasis or river blindness, I think that river-blindness worm is an adequate name.

Adult river-blindness worms live under the skin (in the dermis) of humans, which apparently are the only species that they infect as adults. They have the typical roundworm appearance of any roundworm. Females measure up to 70 cm in length and live inside nodules that they develop under the human skin. Males are much smaller, measuring only 2.3 cm, and can move under the skin from nodule to nodule in search for fertile females.

Three adult males and one adult female of the river-blindness worm. Credits to Hizagi et al. (2014).*

When females are about to release their eggs, they attract males , possibly using pheromones. After mating, the female retains the eggs inside her until the first-stage microfilariae (larvae) hatch. They are then released into the subcutaneous tissue where they wait for a black fly (Simulium damnosum or other species) to bite a human in search for blood. When this happens, the microfilariae end up sucked into the black fly together with the blood.

From the black fly’s gut, the microfilariae migrate to the thoracic flight muscles of the black fly and develop into the first juvenile stage and then into the second. After that they migrate again, now toward the black fly’s proboscis and their salivary glands. In the salivary glands, they mature into the third juvenile stage, which is the infectious stage. The whole cycle inside the blackfly takes about 1 to 3 weeks.

Scan electron microscopy of the head of a female black fly with a juvenile river-blindness worm emerging from her antenna. Credits to the United States Department of Agriculture.

When the black fly bites a human again, the infectious juveniles and delivered via saliva into the bloodstream of the human. From there, they migrate back to the dermis, form nodules and develop into adults over a period of 6 to 12 months, finishing the cycle.

Infected humans develop the disease known as onchocerciasis or river blindness. The main symptom is severe itching, but long-therm infections lead to keratitis (inflammation of the cornea in the eye), which eventually leads to blindness. Onchocerciasis is caused by the microfilariae and the response of the immune system to the infection and not by the adults.

Child with nodules containing the adult worms. Photo extracted from http://www.riverblindnessvaccinetova.org/.

The most effective treatment currently is the use of ivermectin, which kills the microfilariae. It does not kill adults, though, only paralyzing the uterus of females for about 12 to 18 months, preventing them to release more microfilariae during this time. For this reason, a new dose of ivermectin needs to be taken every year as long as adults worms are present. Recent findings, however, suggest that some adult females are developing resistance to ivermectin, which indicates that new treatments need to be developed.

The river-blindness worm is native from tropical Africa, where it probably evolved along with humans. The worms has spread to the Americas, probably during the period of slave trade, and the main non-African countries to have cases of river blindness nowadays are Brazil and Venezuela, but only in isolated regions which are not even close to the dimensions that this disease has in Africa.

River blindness is one of the many neglected tropical diseases, infections that do not receive the adequate investment to allow their control. Despite the considerably good response to the treatment by ivermectin, this is not enough to contain the transmission of the worm, since poor populations that barely have a house to live are even less likely to have the adequate conditions to prevent infections (let alone recurrent infections) in the first place.

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References:

Basáñez, M. G., Churcher, T. S., & Grillet, M. E. (2009). Onchocerca–Simulium interactions and the population and evolutionary biology of Onchocerca volvulus. Advances in parasitology, 68, 263-313.

Higazi, T. B., Geary, T. G., & Mackenzie, C. D. (2014). Chemotherapy in the treatment, control, and elimination of human onchocerciasis. Research and Reports in Tropical Medicine, 5, 77-93.

Osei-Atweneboana, M. Y., Awadzi, K., Attah, S. K., Boakye, D. A., Gyapong, J. O., & Prichard, R. K. (2011). Phenotypic evidence of emerging ivermectin resistance in Onchocerca volvulus. PLoS neglected tropical diseases, 5(3), e998.

Wikipedia. Onchocerca volvulus. Available at < https://en.wikipedia.org/wiki/Onchocerca_volvulus >. Access on 9 December 2020.

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* This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.

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Filed under Disease, Friday Fellow, Parasites, worms

Tagged as Nematoda, nematodes, tropical diseases

by Piter Keo | December 4, 2020 · 8:00 am

Friday Fellow: Damaging Black Fly

by Piter Kehoma Boll

If you live in tropical and subtropical areas, or even in forested temperate areas, you may have had the “opportunity” to meet a black fly. Those annoying little dipterans sneak toward you and bite you without you even noticing. After they fly away they let a small round red mark on your skin that will itch like hell in the next hours or days. But this is the least comparing to all the damage those annoying flies can cause.

And talking about damage, we will focus on a black fly named Simulium damnosum. It does not have a specific popular name, but I decided to call it the damaging black fly.

A damaging black fly on human skin. Credits to Otis Historical Archives of “National Museum of Health & Medicine”**.

The damaging black fly is very similar to other black flies and it is very hard to differentiate them morphologically. Thus, the name Simulium damnosum is often used in the sense of what is identified as the Simulium damnosum complex, a group of very similar species that can only be differentiated through genetic and cytological aspects. Thus, this article will focus mostly on the complex and not the species Simulium damnosum specifically. They are, afterall, basically identical in all relevant aspects, including their ecology.

Adult damaging black flies measure less than 5 mm in length and have a black chubby body. Females feed on both nectar and mammal blood, while males feed only on nectar. The damaging black fly is found in Subsaharian Africa, especially near rivers. Females lay their eggs in well-oxygenated running water, which larvae need to survive. They are very sensitive to pollution and larvae need immersed substrates, such as rocks or vegetation, to which they anchor themselves using small hooks. Females can lay up to 250 eggs per day and they hatch between 36 and 48 hours after laying.

The life cycle is very fast. The larvae feed on floating organic particles and under favorable conditions turn into pupae after about 8 to 10 days. The pupae remains encased in a coccoon, attached to the substrate and does not move. About three days later the adults emerge from the pupae and move toward the surface, taking flight as soon as they leave the water. The adults mate a few hours after emerging from water, but females continue alive for several days, laying hundred, thousands of eggs, and feeding on mammal blood daily.

Pupae and larvae of a species of black fly (probably not *S. damnosum*) in South Africa. Photo by Rob Palmer.*

As a blood-sucking insect, the damaging black fly is the vector of one of the most serious tropical diseases, onchocerciasis or river blindess. This disease is caused by a nematode that spends part of their life cycle in mammals and part in the flies. Onchocerciasis leads to several debilitating symptoms in humans, especially skin problems and glaucoma, which can cause blindness. It is, in fact, the second most common cause of blindness worldwide, making around 250 thousand people become blind every year.

Since damaing black flies cause such a serious disease to humans and since they live near water courses, such areas are almost uninhabitable in many regions of Subsaharan Africa. However, these areas are the most suitable for agriculture, which causes serious economical problems.

Until now, most attempts to reduce the number of black flies have been unsuccessful. The most effective method until now is the use of inseticides but, as you may guess, this does not only kill the black flies, but many other beneficial insects as well and, as soon as an area is free of black flies, it is colonized again by populations for the surrounding areas. Other alternative to reduce the ability of black flies to reproduce is to build dams that will reduce water flow in rivers, turning the water unsuitable for the larvae, but this, of course, can lead to an even worse ecological disaster.

While the countries affected by the disease lack resources to promote research on the subject, the rich countries couldn’t care less about the human population of such places, as we all know. This is a problem that, in a capitalist world, will hardly find a quick and effective solution.

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References:

Jacob, B. G., Novak, R. J., Toe, L. D., Sanfo, M., Griffith, D. A., Lakwo, T. L., … & Unnasch, T. R. (2013). Validation of a remote sensing model to identify Simulium damnosum sl breeding sites in sub-Saharan Africa. PLoS Negl Trop Dis, 7(7), e2342.]

Le Berre, R. (1974). Simulium damnosum. In Control of Arthropods of Medical and Veterinary Importance (pp. 55-63). Springer, Boston, MA.

Post, R. J., Onyenwe, E., Somiari, S. A. E., Mafuyai, H. B., Crainey, J. L., & Ubachukwu, P. O. (2011). A guide to the Simulium damnosum complex (Diptera: Simuliidae) in Nigeria, with a cytotaxonomic key for the identification of the sibling species. Annals of Tropical Medicine & Parasitology, 105(4), 277-297.

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* This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

** This work is licensed under a Creative Commons Attribution-Share Alike 2.0 Generic License.

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Filed under Entomology, Friday Fellow

Tagged as blood-feeding species, Diptera, flies

by Piter Keo | December 1, 2020 · 12:20 am

New Species: November 2020

by Piter Kehoma Boll

Here is a list of species described this month. It certainly does not include all described species. You can see the list of Journals used in the survey of new species here.

Bacteria