Entering April, pig prices have gradually entered the rising stage, and farmers will also usher in their own "spring". However, under the normalization of African swine fever, pig farm biosecurity is still the top priority in pig breeding work, at this time, we farmers must not take it lightly! Because the temperature rise "mosquitoes, flies, rats and insects" will add more uncertainties to the changes in the epidemic! Therefore, we must use this period of spring to do a good job in the pest control of our own pig farms!
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Why april is a critical period for fly control and control of African swine fever
Our country is vast, the temperature is inconsistent, generally in Most areas have risen in April, and flies have begun to appear (the southern region will be earlier). The fly's ability to complete its life cycle depends heavily on climatic conditions. When the temperature is below 15 ° C or above 45 ° C, and the humidity is less than 60% or above 80%, it can well inhibit the growth of flies. The activity of flies is greatly affected by temperature. It can only crawl at 4 ~ 7 ° C, can fly at 10 ~ 15 ° C, can feed, mate and lay eggs above 20 ° C, is especially active at 30 ~ 35 ° C, stops being active due to overheating at 35 ~ 40 ° C, and dies at 45 ~ 47 ° C. Of the entire fly population, 80% are developing and only 20% are adult flies. Therefore, the extinction of flies in April allows the flies to be controlled in the larval stage.
The Russian experience shows that the risk of African swine fever increases explosively when temperatures rise in spring and summer (Figure 1), and that there is a greater need for prevention and control because mosquitoes, flies, ticks, and mice transmit other diseases.
This article focuses on the biological characteristics of flies, the epidemiological characteristics of fly-borne African swine fever virus (ASFV), and the prevention and control of flies.
Moscow temperature conditions in different months of 2018
Figure 1. The situation of African swine fever in Russia and the temperature situation in Moscow in different months of 2018
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Biological characteristics of flies
The feeding habits of flies (Figure 2) are very complex, they belong to omnivorous flies, and can eat various substances, such as human food, secretions and excrement of people and livestock and poultry, kitchen debris and other garbage, and plant juice. After the house flies are full, the interval is very short (a few minutes), you can excrete due to vomiting, frequent excretion, more water loss, and prompt it to frequently eat, the flies' eating habits are very mixed, fragrant, sweet, sour, smelly like, it takes to spit out the sac liquid to dissolve the food, its habit is to eat, while vomiting, while pulling, someone has made observations, in the case of more abundant food, flies have to defecate 4 to 5 times per minute. It causes serious pollution in livestock and poultry farms, and feed and drinking water utensils are often contaminated.
Figure 2. Fly pictures
Biologically, the fly is a completely metamorphosed insect, and its life history can be divided into eggs, larvae (3 ages), pre-pupae, pupae, and adult insects. The life course of a fly is calculated in days, its egg stage is about 1 day, the larval stage is 3 to 6 days, the pupal stage is 3 to 7 days, and it takes only 7 to 14 days from egg development to adult. In a few days to a dozen days, the granular eggs grow into flies (Figure 3). Although the lifespan of a fly is only about 1 month, a female fly can lay 500-1000 eggs. The offspring of a pair of flies contracted a total of 190 million, a staggering number, which shows the great harm of flies.
Figure 3. Life history of flies (image from the Internet)
Characteristics of fly spawning:
The peak period for spawning is from 17:00-19:00 every day. The length of the pre-spawning period (i.e., from feathering to the time of first spawning) of female flies is closely related to ambient temperature: an average of 9 days at 15 °C, only 1.8 days at 35 °C, and no spawning at below 15 °C. After mating, female flies often crawl into the breeding crevices such as human and animal feces, and extend their spawning tubes to lay eggs deep in the breeding organism, so that the eggs are fully protected.
Scope of activities:
Flies are good at flying. The flight speed can reach 6 to 8 km per hour, and the maximum flight speed is 8 to 18 km per day and night. However, it is usually active within a radius of 100 to 200 m in the breeding area, and most of them do not exceed 1 to 2 km.
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Epidemiological characteristics of fly-borne African swine fever virus
3.1 Immature green-headed flies (outdoor flies) cannot host ASFV and cannot be mechanically carried or transmitted by digestion
The green-headed fly is called the red-headed fly (Fig. 4) Calliphora vicina Robineall, taxonomic status: The insect Order Diptera Diptera Diptera, Aristocera Liliphoridae.
Figure 4. Red-headed fly
A species of insect in the subfamily Liliaceae. Worldwide distribution. Adults are 6 to 13 mm long, mostly blue, and not very bright. The body surface powder is densely packed, especially on the chest. The larvae feed mainly on corpses and breed in piles of livestock bones, hairpiles, carcasses and spoilage, and in winter the larvae overwinter in garbage heaps or piles of miscellaneous bones. Adults generally appear in spring and late autumn and are outdoor flies.
In this study (Figure 5), the larvae of pathogen-free mercerizable greenflies and red-headed flies of the family Greenhead Flies were transferred to biosafety level III or IV sites and facilities, fed their larvae with fresh spleen tissue containing African swine fever virus (Estonian ASF genotype II wild strain) for ten days, and fresh ASFV-containing spleen tissue was added during the formative stage of the experiment 2, 4, 7 larvae. Samples were taken at 2, 4, 7, and 10 days of the experiment to detect asFV virus nucleic acid content or to do a hemocytic adsorption test. One batch of samples at each time node is not treated and directly frozen in the -80 °C freezer, and the other batch is washed four times with sterile PBS, and the first two eluates are used for ASFV detection. The experimental results are shown in the following figure: there is a moderate amount of ASFV contamination in the untreated larvae, after washing, the ASFV on the surface of the two flies decreases, but it still contains a moderate amount of ASFV virus, and only a small amount of ASFV contamination or negative is in the pupae of the two washed flies (Figure 6).
It was shown by hematocyte adsorption test that after 7 days of infection, the viral titer in the infected tissue decreased from 1×105 TCID50/10 mg to 5×101 TCID50/10 mg, and in other experimental samples (larvae, pupae, lotion, tissue exposed by larvae) no infective ASFV was detected by hematocrit assay.
One possible explanation is that the saliva secretions of flies act as antibiotics.
Experimental conclusion: Immature green-headed flies cannot act as a host for ASFV and cannot transmit ASFV through mechanical carrying.
Figure 5. Related literature 1
Figure 6. a (Red-headed Fly) and b (Mercerized Green Fly): The amount of ASFV in the unwashed sample, the square is the amount of ASFV in the spleen of the wild boar, and the round is the content of ASFV in the larvae or pupae of the fly.
c (Red-headed Fly) and d (Mercerized Green Fly): The content of ASFV in the washed sample, the white column is the content of ASFV in the washed larvae or pupae, and the gray and black columns are the content of ASFV in the first and second lotions, respectively. (From Forth et al., 2017)
3.2 The widespread stable fly (widespread indoor and outdoor) in China can carry and transmit African swine fever
Stomoxys calcitrans (Figure 7) is a species of insect in the subfamily Stingeridae of the family flies. Also known as the blood-sucking stable fly. Worldwide distribution. Adults are 5 to 10 mm long and gray-brown with brown tinges. He is mainly active during the day, sucking the blood of livestock and occasionally people, and perchs on the sunny cowshed after the temperature drops in autumn. Female flies mostly lay eggs at dusk and rarely during the day. The larvae breed in humus and chicken manure, and the old mature larvae pupate in the soil. In addition to directly affecting the health and productivity of livestock, pathogens such as anthrax and trypanosomiasis can be transmitted.
Figure 7. Stable stinging flies
The following studies have shown that pigs eating asparagus flies that have eaten plasma containing ASFV can be infected with ASFV (Olesen et al., 1a, 2018) (Figure 8).
Figure 8. Related literature 2
Further studies by Olesen et al. have shown that, using quantitative methods, at least 12 h after feeding flies using ASFV-containing blood, ASFV nucleic acids can be detected from the mouthparts of flies, and ASFV nucleic acids can be detected in the brain and body parts of flies within 3 days. Infectious ASFV can be detected from flies at 3 h and 12 h, and the head structure of the stinger fly is shown in Figure 9.
The presence of infectious ASFV after flies consume blood containing ASFV suggests that the stable fly can transmit ASFV. The presence of ASFV nucleic acids in stable flies for 3 days suggests that detecting blood-sucking flies can help us understand the spread of ASFV in the clinic (Olesen et al., 1b, 2018) (Figure 10).
Figure 9. Stable fly structure
Figure 10. Related literature 3
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Control of flies
(1) Physical control of flies
Timely cleaning of feces, and special attention should be paid to the feces and sewage in dead corners, as far as possible to keep the pig house dry; timely and proper treatment of sick and dead pigs; timely cleaning of waste bedding; regular inspection of drinking water and feeding systems to ensure that no water leakage, no spillage. And according to the situation of the pig farm, the following instruments and equipment can be installed in the pig house and the pig farm canteen, with relevant addresses for reference.
Eco-friendly flycatcher (image from the Internet)
Automatic flycatcher Fly exterminator fly trap (image from the internet)
Anti-mosquito lamp Household mosquito repellent lamp anti-fly lamp Commercial restaurant mosquito exterminator electronic mosquito repellent (picture from the network)
(2) Chemical control of flies
Of the flies as a whole, 80% of the population are developing larvae and only 20% are adult flies. Therefore, the control of flies is divided into two parts: adult flies and larvae:
For adult flies: the use of cypermethrin (cypermethrin) + dichlorvos, can also be used to deworm net 5g + sugar 50g to make bait in the pig house, quickly reduce the density of adult flies.
For eggs, pupae, larvae: eliminate insect eggs (adult or insect eggs in fecal piles, floors, fecal ditches, sewers, railings, walls, etc.), use 10% cipromazine 50 ~ 100g / T drinking water or mixture, continuous use for 5 weeks, stop for 5 weeks, and then use for 5 weeks, recycle.
(This article is transferred from leman pig conference, invasion and deletion)