Echinococcus shiquicus
| Echinococcus shiquicus | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Echinococcus shiquicus | ||||||||||||
| Xiao et al. , 2005 |
Echinococcus shiquicus is a parasitic tapeworm from the Taeniidae family. The only known final host so faris the Tibetan fox ( Vulpes ferrilata ), which only lives on the Tibetan plateau. The larvae develop in its main prey, the black-lipped pika ( Ochotona curzoniae ). This tapeworm is unlikely to be pathogenic to humans .
features
Characteristics of the adult animals
Like other Echinococcus species, the full-grown ( adult ) Echinococcus shiquicus consists of a head section, the scolex with a protruding rostellum and a double row of hooks, and then the tapeworm limbs ( proglottids ). In sexually mature animals, the penultimate proglottis carries the male genitalia and the last one, as the egg-bearing (female) proglottis, contains around one hundred eggs which already contain mature larvae, so-called oncospheres .
| E. shiquicus | E. granulosus | E. multilocularis | |
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| Body length (mm) | 1.3 to 1.7 | 2.0 to 11.0 | 1.2 to 4.5 |
| Number of segments | 2 to 3 | 2 to 7 | 2 to 6 |
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Length of the large hooks on the rostellum (μm) |
20.0 to 23.0 | 25.0 to 49.0 | 24.9 to 34.0 |
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Length of the small hooks on the rostellum (μm) |
16.0 to 17.0 | 17.0 to 31.0 | 20.4 to 31.0 |
| Number of testicles | 12 to 20 | 25 to 80 | 16 to 35 |
The anatomy of the adult Echinococcus shiquicus largely corresponds to that of the fox tapeworm ( Echinococcus multilocularis ), but Echinococcus shiquicus is significantly smaller than the related species. Adult animals reach a body length of 1.2 to 1.7 millimeters, while adult fox tapeworms 1.2 to 4.5 millimeters and tripartite dog tapeworms ( Echinococcus granulosus ) even 2 to 11 millimeters long. They also have only two to a maximum of three proglottids, while both the fox tapeworm and the tripartite dog tapeworm can have up to six or seven proglottids.
The hooks in the terminal wreath of hooks, the rostellum of the Scolex, are also significantly smaller than those of the related species and the number of testes of the sexually mature proglottis is significantly lower. They also differ in terms of the number of eggs , which is around 100 eggs in Echinococcus shiquicus and several hundred eggs in other species. Other differences concern the position of the genital pore, which is here near the upper end of the sexually mature proglottis, and the sac-shaped egg-bearing proglottis with an unbranched uterus .
Genetic traits
Echinococcus shiquicus was discovered primarily due to genetic differences from the known species Echinococcus multilocularis and Echinococcus granulosus and identified as a separate species. These were different genes of mitochondrial DNA , such as cox1 , nad1 , atp6 and above all cob . Subsequent investigations have revealed that other parts of mitochondrial and nuclear DNA ( nuclear DNA ) are known today.
distribution
The range of Echinococcus shiquicus is likely limited to the highlands of Tibet where its hosts live. Since the tapeworm has not yet been found in other fox species that also live on the Tibetan high plateau (especially the red fox ( Vulpes vulpes ) and the steppe fox ( Vulpes corsac )), further distribution is unlikely.
Way of life and life cycle
Echinococcus shiquicus has so far only been identified as a larva in the black-lipped pika ( Ochotona curzoniae ) as an intermediate host and as an adult only in the Tibetan fox ( Vulpes ferrilata ) as the final host .
The life cycle corresponds to that of other Echinococcus species: the foxes prey on pigeon hares that are infected with the fin stages of Echinococcus shiquicus , and with the meat they also take in the fins contained in the hydatids . These develop in the fox's gastrointestinal tract into adult tapeworms, which establish themselves in the small intestine of the fox, especially in the ileum , and here produce eggs in the egg-bearing proglottids. As the ultimate host, the fox can be infested with hundreds to tens of thousands of tapeworms. As with other final hosts of Echinococcus species, it can also be assumed with this species that an infection only has a negative effect on the health of the foxes if there is a very large number of tapeworms.
The proglottids filled with eggs are released into the intestinal lumen and get out with the foxes' feces . The whistle hares ingest the proglottids and the eggs they contain with contaminated vegetable food and the eggs develop into larvae, the oncospheres , which enter the blood vessel system in the small intestine and establish themselves in the body tissue. Here they form, mainly in the liver and lungs, through asexual reproduction, individual, approximately 10-centimeter-large fin bladders ( hydatids ), which correspond to the cystic echinococcosis of the tripartite dog tapeworm. These are likely to lead to severe health impairment up to death in the little pipefish, but no relevant studies are available yet. In the bubbles, the developed Metazestode as the second larval stage of the tapeworm. The metacestodes form numerous budding daughter larvae through asexual reproduction in the bladder wall, which consist exclusively of an inverted head (scolex) with a sprouting zone and are called protoscolices . Daughter bubbles in the hydatide are not formed.
Systematics
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| Two different phylogenetic trees based on mitochondrial DNA (mtDNA) and nuclear DNA ( nuclear DNA ). The brackets stand for different genotypes . |
The first scientific description of Echinococcus shiquicus was made by Ning Xiao et al. 2005, who, during molecular biological studies of larval material from the Shiqu region, came across DNA in different intermediate hosts that differed significantly from the known sequences. The material came from the tissue of the black-lipped pika and the authors were able to detect the same sequences in the tapeworms of the Tibetan fox. The newly described species was named shiquicus after the Shiqu region .
A first discovery and scientific presentation probably goes back to Guo et al. Back in 1993, who traced the Finnish bladders they described in the tissue of the pika back to Echinococcus granulosus . Qiu et al. 1995 described atypical adults of Echinococcus multilocularis from the intestines of Tibetan foxes, and according to the first person describing it, this was also a description of the adult animals of Echinococcus shiquicus .
The systematics of the genus Echinococcus and thus also the systematic position of Echinococcus shiquicus has not yet been conclusively clarified. The main problem here are the numerous forms of Echinococcus granulosus described as genotypes (designated as G1, G2, etc. in the cladograms) , which cannot be recognized as monophyletic clades in previous molecular biological investigations . In the current literature and therefore also in the adjacent cladograms, some of these are already regarded as separate species E. equinus , E. ortleppi , E. canadensis and E. intermedius . The species status of Echinococcus shiquicus and the assignment to the genus Echinococcus have been documented since the first scientific description by Ning Xiao et al. Generally recognized in 2005.
The previous molecular biological investigations on the systematics of the Echinococcus species are based on mitochondrial and nuclear DNA (core DNA). The results of these two studies differ significantly: When using the nuclear DNA, E. multilocularis and E. shiquicus represent the two basal species of the genus and the different genotypes of E. granulosus form a taxon with E. felidis . When using mitochondrial DNA, however, these two species are placed in the middle of the E. granulosis genotypes.
Saarma et al. 2009 advocate the use of the core DNA to determine the phylogenetic relationships , since the mitochondrial DNA in this case of the parasitic way of life does not trace the actual development of the species due to its random mutation rate without recombination . According to this analysis, Echinococcus multilocularis is the most basic species of the genus, followed by E. shiquicus .
Epidemiology and relevance to humans
Epidemiological studies on the infestation frequency of Echinococcus shiquicus are not available for the Tibetan fox as the final host or for the black-lipped pika.
In the highlands of Tibet Echinococcus shiquicus occurs together with the fox tapeworm and the tripartite dog tapeworm. All three species can attack the domestic pigeon rabbits and other small mammals as intermediate hosts, but only the fox tapeworm and Echinococcus shiquicus have been identified as final hosts in the Tibetan fox . It can also lead to double infections of individual pika or foxes with both types of tapeworm. A double infection has so far only been proven in one pika who had both fins of Echinococcus shiquicus and Echinococcus multilocularis in its liver .
Echinococcus shiquicus has not yet been detected in humans and is probably not pathogenic for humans . In a study in which a total of 68 cases of echinococcosis in northwest China were examined using molecular biological methods to identify pathogenic Echinococcus species, no infections with Echinococcus shiquicus could be detected. The potential of Echinococcus shiquicus as a zoonotic agent is unknown.
supporting documents
- ↑ a b c d e f g h i j k Ning Xiao, Jiamin Qiu, Minoru Nakao, Tiaoying Li, Wen Yang, Xingwang Chen, Peter M. Schantz, Philip S. Craig, Akira Ito: Echinococcus shiquicus n. Sp., a taeniid cestode from Tibetan fox and plateau pika in China. International Journal for Parasitology 35 (6), 2005; Pp. 693-701. ( Abstract ).
- ↑ a b c d e f M. Nakao, DP McManus, PM Schantz, PS Craig, A. Ito: A molecular phylogeny of the genus Echinococcus inferred from complete mitochondrial genomes. Parasitology 134 (5): pp. 713-722. PMID 17156584
- ↑ a b c d e f g h U. Saarma, I. Jõgisalu, E. Moks, A. Varcasia, A. Lavikainen, A. Oksanen, S. Simsek, V. Andresiuk, G. Denegri, LM González, E. Ferrer, T. Gárate, L. Rinaldi, P. Maravilla: A novel phylogeny for the genus Echinococcus, based on nuclear data, challenges relationships based on mitochondrial evidence. Parasitology 136 (3), 2009: pp. 317-328. PMID 19154654
- ↑ Vulpes ferrilata in the endangered Red List species the IUCN 2011. Posted by: Schaller & Ginsberg, 2004. Accessed December 25, 2011th
- ↑ a b c Ning Xiao, Jiamin Qiu, Minoru Nakao, Tiaoying Li, Wen Yang, Xingwang Chen, Peter M. Schantz, Philip S. Craig, Akira Ito: Echinococcus shiquicus, a new species from the Qinghai – Tibet plateau region of China : Discovery and epidemiological implications. Parasitology International 55 (Supplement), 2006; Pp. S233-S236. ( Abstract ).
- ↑ ZX Guo, DL He, Y. Q Li, GQ Zhao, YF Ma, PY Liu, et al. : Survey of endemic situation and natural foci of hydatidosis in Qinghai - Tibet plateau. International Archives of Hydatidoses 31, (1993); P. 69.
- ↑ JM Qiu, XW Chen, M. Ren, CX Luo, DL Liu, XT Liu, et al. : Epidemiological study on alveolar hydatid disease in Qinghai - Xizang plateau. Journal of Practical Parasitic Diseases 3, 1995: pp. 106-109. PMID 19154654
- ↑ a b Ning Xiao, Minoru Nakao, Jiamin Qiu, Christine M. Budke, Patrick Giraudoux, Philip S. Craig, Akira Ito: Dual infection of animal hosts with different Echinococcus species in the eastern Qinghai-Tibet plateau region of China. The American Journal of Tropical Medicine and Hygiene 75 (2); Pp. 292-294.
- ↑ T. Li, A. Ito, K. Nakaya, J. Qiu, M. Nakao, R. Zhen, N. Xiao, X. Chen, P. Giraudoux, PS Craig: Species identification of human echinococcosis using histopathology and genotyping in northwestern China. In: Transactions of the Royal Society of Tropical Medicine and Hygiene. Volume 102, number 6, June 2008, pp. 585-590, doi : 10.1016 / j.trstmh.2008.02.019 , PMID 18396303 , PMC 2517144 (free full text).
- ↑ Pedro Moro, Peter M. Schantz: Echinococcosis: a review. International Journal of Infectious Diseases 13, 2009; Pp. 125-133.
literature
- Ning Xiao, Jiamin Qiu, Minoru Nakao, Tiaoying Li, Wen Yang, Xingwang Chen, Peter M. Schantz, Philip S. Craig, Akira Ito: Echinococcus shiquicus n. Sp., A taeniid cestode from Tibetan fox and plateau pika in China. International Journal for Parasitology 35 (6), 2005; Pp. 693-701. ( Abstract ).
- Ning Xiao, Jiamin Qiu, Minoru Nakao, Tiaoying Li, Wen Yang, Xingwang Chen, Peter M. Schantz, Philip S. Craig, Akira Ito: Echinococcus shiquicus, a new species from the Qinghai – Tibet plateau region of China: Discovery and epidemiological implications. Parasitology International 55 (Supplement), 2006; Pp. S233-S236. ( Abstract ).
