Rat flea
| Rat flea | ||||||||||||
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Rat flea |
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| Xenopsylla cheopis | ||||||||||||
| ( Rothschild , 1903) |
The rat flea ( Xenopsylla cheopis , but often incorrectly spelled cheopsis ), also known as plague flea , Indian rat flea , tropical rat flea , belongs to the fleas (Siphonaptera). It used to be called Pulex cheopis .
features
The male rat fleas are 1.4 to 2 mm long, the female rat fleas 1.9 to 2.7 mm long. In contrast to dog and cat fleas , they do not have spiked combs on their heads.
As host to the blood-sucking rat flea different serve rodents , including the widespread brown rats and black rats as well as humans. The original hosts, however, are obviously the Egyptian grass rats ( Arvicanthis niloticus ), from which the flea is said to have switched to the house rats.
The rat flea as a disease carrier
Transmission mechanism
The rat flea is one of the main vectors of the plague . It sucks up the bacteria ( Yersinia pestis ) with the blood . In 1914 it was discovered that fleas that had sucked pest-infected blood could no longer suck up blood after a few days despite exertion: the forestomach (proventriculus) was clogged with clumped bacteria. The exertion causes the esophagus to widen so that a significant amount of bacteria is expelled backwards into the bite. This is how they get into the human bloodstream. The bacteria are not immediately fatal for the flea, especially if they are only partially blocked, they can survive for a while, even if their lifespan is noticeably shorter. But if the temperature is too high or the humidity is too low, they lead to its drying out. This could explain the sudden end of the epidemics in India in hot dry weather. These investigations and conclusions related exclusively to the bubonic plague that occurred in India at the time .
Vector effectiveness
How effective certain types of fleas are in spreading the plague is called "vector effectiveness". CM Wheeler , JR Douglas and AL Burroughs determined the vector effectiveness as a product of three forms of potential: 1) The infection potential, i.e. H. how many individuals in a flea population suck blood on hosts infected with plague bacteria. 2) the infectious potential, i.e. how many of these fleas can cause a plague by themselves because the digestive tract is blocked. 3) Transmission potential: How many times can a single flea transmit the infection before it dies or the blockage is broken. The vector index was then introduced in order to be able to compare the various flea species with one another on this point; A total of around 80 flea species, which occur in association with around 200 wild rodent species, have been identified as carriers of the plague bacterium in the field or have been infected with it experimentally. Xenopsylla cheopis was repeatedly proven to be the most effective vector, while, for example, the closely related Xenopsylla astia does not play a role as a vector.
In 1911 it was discovered that there are differences in the uptake of human blood between species of flea. Most species of fleas were locked into specific host animals that they preferred. It turned out that Xenopsylla cheopis and Ceratopsyllus fasciatus (now Nosopsyllus fasciatus ) accept human blood. Xenopsylla cheopis , however, is fixated on tropical environments and it is doubtful that it occurred in Europe. In England only one proof was successful ( Plymouth ). Rothschild also mentions occurrences in ship rats in southern Italy and Marseille , where they quickly disappeared.
Influence of temperature
Dan C. Cavanaugh noted that temperature is the single most important factor blocking the flea's digestive system. When examining the environmental parameters of the annually occurring plague waves, a connection between the size of the flea population and the temperature between 10 ° C and 30 ° C was found. Cavanaugh discovered that the clumps of bacteria disintegrated by themselves at temperatures> 27 ° C using an enzyme that destroys the fibrins that hold the clumps of bacteria together. This reduced the concentrations in the flea to such an extent that they no longer had enough bacteria to effectively infect them. This effect had already been observed in the Vietnam War in 1966. These results were all obtained for Xenopsylla cheopis .
Pathogen concentration
When infected dead rats were examined, a concentration of> 10,000 up to 100 million and 1 billion plague bacteria / milliliter of blood was found. In people shortly before their death (lethal phase) the concentration was far lower. Few of them had concentrations higher than 10,000 bacteria / ml blood. This difference plays a role in the question of whether the plague can be transmitted directly between people through flea bites, because the flea does not ingest more than 0.5 microliters of blood at one meal . Therefore the blood sucked up by him must have more than 10,000 bacteria / ml blood for effective infection. This in turn makes it necessary to infer the rat as an intermediate host .
More diseases
The rat flea is also considered to be a vector of mouse spotted fever . In this case it excretes the pathogens ( Rickettsia typhi ) with the faeces. The victim scratches himself and the stab wound or other injury causes the pathogen to get into his victim's bloodstream.
Individual evidence
- ^ NC Rothschild : New species of Siphonaptera from Egypt and the Soudan. In: Entomologist's Monthly. 1903, No. 39, pp. 83-87, PDF of the entire volume; First description of Pulex cheopis from page 85 .
- ↑ Ilka Lehnen-Beyel: New suspects: Did Egyptian wild rats bring the plague to humans? February 19, 2004, accessed September 7, 2019 . In: Bild der Wissenschaft - online .
- ↑ AW Bacot, CJ Martin: Observations on the Mechanism of the Transmission of Plague by Fleas. In: Journal of Hygiene. Vol. XIII, Plague Supplement III, 1914, pp. 423-439.
- ^ CM Wheeler, JR Douglas: Sylvatic plague studies V, The determination of vector efficienty. In: The Journal of Infectious Diseases . 77, 1945, pp. 1-12.
- ^ AL Burroughs (1947): Sylvatic plague studies. The vector efficiency of nine species of fleas compared with Xenopsylla cheopis. In: Journal of Hygiene 45: 371-396.
- ↑ B. Joseph Hinnebusch (2005): The Evolution of Flea-borne transmission in Yersinia pestis. In: Current Issues in Molecular Biology 7: 197-212.
- ^ Henriette Chick, CJ Martin: The Fleas Common on Rats in Different Parts of the World and the Readiness with wich they Bite Man. In: Journal of Hygiene. Vol. XI, No. 1, 1911, pp. 122-136.
- ^ N. Charles Rothschild: Note on the species of flesas found upon rats, 'Mus rattus' and 'Mus decumanus', in different parts of the worlds, and on some variations in the proportion of each species in different loclities. In: Journal of Hygiene. Vol. VI, No. 4, 1906, pp. 483-485.
- ^ Dan C. Cavanaugh: Specific effect of Temperature ubon Transmission of the Plague Bacillus by the Oriental Rat Flea, Xenopsylla cheopis. In: The American Journal of Tropical Medicine and Hygiene. 20, 1971, pp. 264-273.
- ↑ In: Journal of Hygiene. Vol. VIII, No. 2, 1908, pp. 266-301.
- ↑ In: Journal of Hygiene. Vol. VI, No. 4, 1906, pp. 519-523.
- ↑ In: Journal of Hygiene. Vol. VI, No. 4, 1906, pp. 524-529.