Team:HZAU-China/Safety/the Safety of Flea

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Further works

Fleas are main vectors which may spread plague, endemic typhus and other diseases. In our project, we had carefully considered the further works if we would use of the fleas. How well do the fleas will influence in environment, which fleas’ species should we choose and is it worth to take rises of the plague and other diseases to fight against rabies with the fleas?

Plague and people

When a flea-borne diseases are mentioned, people first thought is the plague. Also, plague is under strict observation as the most dangerous group in China.

At the beginning of 20th century, Pavlovsky proposed a concept: when a disease in natural world does not depend on the existence or activity of human, it iscalled natural foci disease. Only when human occasionally involved in the disease cycle in nature, there may be an infection. Plague is the natural foci disease. The plague pathogen Yersiniapestisis obligatory parasitism[1]that cannot survive and transmit distantly along without hosts.(Fleas do well in jumping but are bad at moving，So fleas also transmit by their hosts and that’s why there will be a lot of mice before the pandemic).So the range of activity ofhosts and vectors is the natural geographical barriers of plague.

The pictures below are the map of plague focustypes in China and the Chinese lisarithmic map. Comparing two pictures, we will find that most of natural epidemic foci are far away from densely populated areas.Moreover, the distribution of thestray dogs is just reverse.So if we focus on deratizationand closely monitor the natural epidemic foci, there is remote possibility that the clean fleas we released will be infected by Yersiniapestis.(Yersiniapestis cannot vertically transmit in fleas, which means that the fleas will clean the Yersiniapestisin case of no external input source by reproduction.In fact,many researchers catch wild fleas from where never been polluted by plague and breed them for clean fleas.)

The hosts, fleas and people

Here is a diagram to show the plague transmission way. The following tips is the supplementary to the picture.

1.hosts

In china, all identified main hosts in natural foci are rodents. Carnivores are infected by preying the infected rodents. Studies have shown that in the domesticated animals, dogs are not high sensitivity to plague.[1]

Flea mouthparts can only pierce the epidermis. So, only Yersinia pestis be in the whole host’s body, including the finest capillaries under the skin that the fleas can be infected.in fact, there is only the dying main hosts can match this condition. And it called bacteremia. Dogs are not sensitivity enough to got bacteremia.

2.Hosts direct infect humans

The circumstances that hosts direct infect humans mainly occurs in hunting or skinning wildlife, especially Marmota himalayana.[2] As long as you don’t directly contact with wild animals in the natural epidemic foci, there will be no risk to be direct infected the plague.

3.Fleas

Yersinia pestis cannot vertical transmit in fleas[3]. To fight against plague, we should pay attention on the main host. History shows that deratization can successful eliminate the natural epidemic foci in China.[4]

Not all species of fleas are main vectors of plague. There are only more than ten kinds of fleas are main vectors in China. [5]We found that the cat fleas(Ctenocephalides felis) don’t have the bad record in plague history, so we choose it as our candidate. Of cause, it should be tested by kinds of experiment.

Only considering the main vector is not complete. There can’t be only one species of fleas in an area. So, we should add the other fleas’ species in it. The fleas which are the main transmission of plague must occupy a certain position in the community then they can play the role as the main vector. It’s called the mass effect.[6] So, if we input the cat fleas in an area, they may replace the dominant position of the main vector and lower the risks of the plague.

Growth and reproduction of fleas significantly affect by the environment. And the dust is the important environmental factor to the larval growth. Has covered with the ground, house which has the better sanitary conditions is not suitable for larval fleas’ survival. So, we nearly never see the fleas in house unless you have pets in cities. If you have pets, keeping your pets clean can prevent fleas into your room.

Current situation

Fleas can spread many diseases. But the most significant diseases have two, one is plague, another is typhus. We got the patients and deaths data of these diseases during 2008-2012 from Chinese Center for Disease Control and Prevention.

As we can see, plague and typhus have been very good control in China. But the death of rabies stays at a high level.so rabies prevention and control works are extremely important in China. This is the reason why we try more ways to solve this issue.

Reference

[1][2][3][4][5][6] Dongzheng Yu. Plague,Epizootiology[M]. Science Press, 2009: 31，31,35,62-65,36-37,55-56