At the same time as the rapid development of the pig industry, the diseases in the pig farm are also changing, and now the mixed infection of two or even multiple pathogens has replaced the separate infection of the pathogen, making the disease of the pig farm increasingly complex, diversified, and more difficult to purify. In recent years, the diarrhea of newborn piglets has spread rapidly in large-scale pig farms in some parts of China, which has seriously affected the healthy development of the pig industry, and has gradually become one of the major diseases affecting the economic benefits of China's pig industry because of its high mortality rate.
The main target of diarrhea in newborn piglets is nursing piglets and early weaning nursery pigs, pigs at this stage are in the decline of maternal antibody protection, autoimmunity is not perfect, digestive system function is not perfect, and in the weaning, mixed group stress and feed replacement period, pigs are very susceptible to disease. Newborn piglet diarrhea is a disease caused by the interaction of viruses, bacteria, parasites, poor feeding management conditions and susceptible pig herds, the incidence is generally 30-80%, the mortality rate is 10-100%, and the younger the pig age, the higher the mortality rate. Sick pigs are characterized by diarrhea, dehydration, anorexia, and rapid wasting, and their main targets are nursing piglets and piglets before and after weaning. At this stage, pigs have poor body temperature ability, lack of innate immunity, underdeveloped digestive organs, incomplete digestive gland function, or in the period of weaning, mixing and word material replacement, pigs are prone to disease.
Pathogens that cause diarrhea in piglets can be broadly divided into three categories: viruses, bacteria and parasites.
Viral pathogens include porcine epidemic diarrhea virus (PEDV), infectious gastroenteritis virus (TGEV), rotavirus (RV), swine adenovirus (PAV), porcine reovirus (REOV), etc.;
Bacterial pathogens include enterotoxin-producing Escherichia coli (ETEC), C. perfringens, salmonella (iSalmonella), etc.;
Parasitic pathogens include Coccidia and Strongyloidesstercoralis.
In addition, stress factors such as excessive pig breeding density, poor air quality, poor ventilation in pig houses, excessive temperature changes, malnutrition of pigs, and decreased immune function may become the triggers for diarrhea outbreaks in piglets.
1. Porcine epidemic diarrhea virus
Porcine Epimic Diarrhea (PED), caused by porcine epidemic diarrhea virus, is a highly exposed intestinal infectious disease characterized by vomiting, diarrhea and decreased appetite, susceptible to pigs of all ages. The epidemiological features, clinical symptoms, and pathological changes of the disease are very similar to those of porcine infectious gastroenteritis.
Prevention of PED: antibiotic therapy for this disease is ineffective, and vaccination is the main means of preventing PED. Due to the small age of the disease, the rapid onset of the disease, and the high mortality rate, it is impossible to rely on autoimmunity, so most of them rely on specific antibodies in colostrum to provide protection for piglets by giving preventive injections to sows. Vaccines are currently considered reliable, but not all sows produce effective milk immunity.
In areas where the disease is endemic, artificial oral infection of pregnant sows in the first 2 weeks of the first 2 weeks of the disease can be carried out with the feces or intestinal contents of the disease to stimulate their milk immunity and shorten the epidemic time of the disease.
2. Infectious gastroenteritis in pigs
Transmissible Gastroenteristis (TGE) is an acute intestinal infectious disease in pigs caused by porcine infectious gastrointestinal virus, which is characterized by fever, vomiting, severe diarrhea, dehydration and high mortality of piglets under 2 weeks of age, which belongs to the pig diseases that must be quarantined in the Class B diseases specified by the World Organisation for Animal Health (OIE). Pigs of all ages are susceptible, with piglets up to 100% mortality rates over 10 days of age and low mortality rates for pigs over 5 weeks of age.
TGE can manifest as endemic, endemic, and cyclical endemic. The incidence and prevalence of TGE is distinctly seasonal, with the peak period of incidence in January and February. TGEV mainly infects pigs, sick pigs and invisible poisoned pigs are the main source of infection of the disease, the virus through feces, milk, nasal fluid, vomit and exhaled gas pollution of the environment, drinking water, feed and utensils, etc., through the digestive tract and respiratory tract to susceptible pigs. Dogs, cats, and birds with poisons do not become infected, but they may be transmitted as vectors and carriers.
The incubation period of the disease is short, generally 15-18 hours, and some as long as 2-3 days. Piglets have a sudden onset of illness, first vomiting, followed by frequent watery diarrhea, yellow-green or white stools, often mixed with undigested curd blocks. Sick pigs are severely dehydrated, their weight drops rapidly, the younger the day-old age, the more serious the disease, the shorter the course of the disease, and the higher the mortality rate. Piglets within 10 days of age die within 2-7 days, and the sick piglets are stunted. Adult pigs generally do not die, usually have only a few days of loss of appetite, and a few pigs experience vomiting and watery diarrhea.
Ocular pathological changes are often confined to the gastrointestinal tract. The stomach is filled with clotted lumps, and there may be small bleeding areas on its diaphragm side. The small intestine is often filled with a yellow liquid that contains foam and undigested clotted pieces. The intestinal wall is thin and transparent, the mesenteric membrane is hyperemic, and the mesenteric lymph nodes are enlarged. Microscopic examination showed that the jejunal villi became significantly shorter, and the mucosal epithelial cells degenerated and fell off. Intestinal epithelial cells are flattened or square immature cells after degeneration.
TGE prevention: There is no effective treatment drug at present, so it is necessary to focus on prevention and take comprehensive prevention. Usually pay attention to strengthening health management, do a good job of daily disinfection, and pay special attention to not introducing seeds from epidemic areas to avoid the introduction of pathogens. Pregnant sows can be vaccinated through the mouth, nose and mammary glands about 20-40 days before delivery, so that the nursing piglets after birth can obtain maternal antibodies. Infection with TGE can be treated with intravenous glucose sodium chloride solution, electrolyte supplementation, and symptomatic treatment of nutrients.
3. Rotavirus
Rotavirus (RV) is one of the main pathogens that cause thirst in a variety of newborn and juvenile animals, characterized by diarrhea and dehydration. At present, RV exists in most pig-raising countries, and the resulting diarrhoeal diseases have brought huge losses to the pig industry.
Epidemiology: In pig-rearing countries, RV infection is widespread, occurring in late autumn, winter, and early spring. Sick and latently infected pigs are the main source of infection. Group A RV is the most dominant pig RV detected in belly pigs, often infecting piglets under 60 days of age, and prevalent in piglets aged 3-5 weeks. The virus is usually present in the intestine, is excreted with feces, and lasts from 1 to 14 days, with an average of 7.4 days. The virus is mainly transmitted by the fecal-oral route, which is endemic, and whether it can be transmitted through the respiratory system needs to be further studied. The virus mainly induces cellular immunity, but the immunity period is not long, so the cured animal can be re-infected.
Clinical symptoms and pathological changes: rotavirus infection with sterile pigs or uneaten suckling piglets aged 1-5 days can cause severe diarrhea. After 12-24 hours of vaccination, pigs are mentally weak, anorexia, and occasionally vomit. Severe after l-4h drainage of yellow-white thin stool, containing different degrees of flocculents. Diarrhea can last for 3 to 7 days and gradually resolve within 7 to 14 days. Diarrhea piglets are dehydrated, and death can occur after 2-5 days of illness, with a mortality rate of 50% to 100%. With increasing age, mortality decreases. Pigs over 14 days of age rarely die. Natural infection with RV in pigs usually does not cause significant clinical symptoms or is a recessive passage.
Lesions are mainly limited to the digestive tract. Young piglets have a slow stomach wall, the stomach is filled with curd and milk, the intestinal wall of the small intestine becomes thinner, the contents are liquid, and sometimes the mucous membrane of the small intestine is striped or diffuse bleeding. Histological examination reveals that the small intestinal line hairs are atrophied and shortened, the apex is peeled off or covered by swollen or damaged near-lindrup-like epithelial cells, crypt cell proliferation, and lymphocyte infiltration of the lamina propria.
Prevention and control: There is currently no specific drug for the treatment of RV infection in pigs. General supportive care is recommended for symptomatic therapy, including antibiotics, antiendocrine drugs, adsorbents, and liquid electrolytes. Reduce the load of susceptible porcine viruses by improving management measures, strengthen passive immunity, and reduce mortality. Strengthen hygiene management, and thorough cleaning and disinfection of houses between different batches of pigs can reduce the infection of pigs.
4. Reovirus
Reoviridae is a large family of viruses with hundreds of viral members belonging to the existing nine established genera and two proposed genera, which can widely infect various organisms in nature and can lead to various pathological reactions in the body. Among them, according to the host species, antigen characteristics, hemagglutinin and the ability to cause cell fusion, members of the genus orthoprovirus can be divided into mammalian reovirus and avian reovirus.
Mammalian reoviruses, commonly known as reoviruses, mainly infect humans and mammals and are widely pathogenic to animals. In 2005, Zeng Zhiyong et al. detected reovirus from the abdominal faeces of piglets suspected of "winter diarrhea", indicating that porcine reovirus may be related to this type of disease. Up to now, there are 3 known porcine reovirus serotypes, which are widely present in pigs and have certain pathogenicity to pigs. Studies have shown that after piglets are infected with human reotracheal lone virus, there may be an instantaneous increase in body temperature, while the virus can be detected again in the stool sample, and the virus is still infectious.
Basic characteristics of viruses: The family Reoviridae is named after a combination of three English words, respiratory tract, gut, and orphans, which can infect both the respiratory tract and the gastrointestinal tract. This type of virus was originally classified as echo virus (enteric_cytopathogenic human orphan virus, a pathogenic virus of human intestinal cells), called ECH010.
5. Enterotoxin-induced Escherichia coli
Enterotoxin E. coli is the pathogen that causes the E. coli in the periety of newborn piglets, which can cause severe watery diarrhea and rapid dehydration death in newborn piglets, with high morbidity and mortality, bringing serious economic losses to the breeding industry. '
It is characterized by diarrhea, the extent of which is related to virulence factors, piglet daily age and immune status, and in severe cases, clinical manifestations are dehydration, metabolic acidosis and death, and sometimes young pigs die without diarrhea. Piglet yellow diarrhea incubation period is short, 12 hours after birth can be onset, piglets have intense diarrhea, yellow loose stool, severe dehydration, short course of disease, rapid onset. The intestines are distended, containing a large amount of yellow liquid contents and gas, and the mesenteric lymph nodes have diffuse bleeding spots.
Piglet diarrhea is also known as late-onset E. coli disease, piglet appetite decreased, emaciated, coarse hair, feces are white or grayish white, smelly, long course of illness, after recovery may become zombie pigs. There are catarrhal inflammatory changes in the intestinal mucosa, mild swelling of the mesenteric lymph nodes.
When the disease is acute, it is often too late to treat it, so the control of this disease focuses on prevention. At present, for the diarrhea of piglets caused by ETEC, the main prevention and control measures are: (1) the use of antibacterial drugs, but due to the increasingly wide range of resistant strains of E. coli, the efficacy is not good; (2) the use of ETEC bacteria or engineered seedlings to immunize pregnant sows, through the colostrum to transmit antibodies to piglets, can provide effective protection for piglets, but the passive immune protection provided by maternal antibodies is difficult to maintain for a long time; (3) Oral specific foreign antibodies can directly protect piglets, but the technical requirements are high, the cost is expensive and the yield is low.
6. Spore coccidioides such as pigs
Isospora Coccidiosis is a disease of the digestive tract of piglets caused by isospora coccidiosis that parasitizes the isospore genus within the epithelial cells of the piglets. The disease is worldwide and has strict host and parasitic site specificity. Coccidioides such as pigs are the most pathogenic protozoa in piglets.
Spore coccidioides such as pigs are distributed worldwide. At present, some Countries in the Americas and Europe, as well as Asian countries, have taken spore coccidioides such as pigs as one of the main causes of abdominal thirst in piglets aged 7-14 days. Especially in some intensive breeding farms, spore coccidioides such as pigs often cause diarrhea in piglets, and more than 20% of piglet diarrhea is caused by spore coccidioides such as pigs, which causes great trouble and economic losses to pig production. The results of studies have shown that sows are not the main source of spore coccidiosis infections in piglets, but it is still unclear how spore coccidiosis infections in pigs are established in pig farms.
Control: By adding anticoccidial drugs to piglet drinking water, or mixing the drugs with oral iron preparations, it may have a certain effect on the treatment of swine coccidiosis, but it does not guarantee that each pig will receive an adequate dose of administration. An effective anticoccidial drug has not yet been identified, and aminopropanline, furazolidone and monensin are not effective in the prevention and treatment of neonatal boar coccidiosis. Studies have shown that it is not advisable to predict the anti-worm effect of coccidioides in weaned piglets or fattening piglets with anticoccidial drugs.
Focusing on sanitation is by far the best way to reduce losses caused by neolial coccidiosis. Do a good job of cleaning the delivery room, completely remove the tissue fragments in the delivery room, and disinfect it for several hours or fumigation with a concentration of not less than 50% bleaching powder or ammonia complex. Keepers should be restricted from entering the delivery room to prevent them from being brought into the egg sac through shoes or clothing, and rat control measures should also be taken to prevent the mechanical transmission of egg sacs by rats. The pen should be disinfected again after each delivery to reduce the chance of infection with coccidiosis in newborn piglets.
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