As farming standards continue to improve and residents’ consumption of and demand for pork products continue to grow, pig farming in China has expanded in scale. The current numbers of pigs in stock and pigs marketed have both increased compared with the past. At the same time, China’s pig industry faces unprecedented challenges as it continues to develop. The greatest challenge for the industry and pig farmers is the growing number of pig diseases, along with the increasing difficulty and cost of prevention and treatment. This is especially true for growing and fattening pigs: disease can cause farmers substantial economic losses. This article briefly reviews the clinical signs, prevention, and control of several common and particularly harmful diseases affecting growing and fattening pigs in the current pig farming industry.
China has a long history of pig farming and is one of the world’s major pig-producing countries. The efficiency of China’s pig industry is currently improving. However, environmental pollution and the increasingly frequent movement of pigs have made various epidemics and diseases a serious threat to China’s pig industry. Pig diseases in China are diverse. By causative agent, common pig diseases can be divided into 3 categories: viral diseases, bacterial diseases, and parasitic diseases. These diseases pose significant challenges for disease prevention and control on pig farms. Therefore, during the growth of fattening pigs, farms should develop appropriate prevention and control measures based on their own circumstances. This article summarizes the clinical signs of several pig diseases that have frequently affected growing and fattening pigs and caused considerable harm to the pig farming industry in recent years, and proposes corresponding prevention and control measures.
I. Clinical signs of several common pig diseases
1.1 Classical swine fever: The United States, the first country in the world to identify classical swine fever, had discovered the disease as early as the beginning of the 18th century. It subsequently spread widely, having a significant impact on the livestock industry. It is listed by the authoritative organization OIE as an extremely serious infectious disease. As land and sea connections gradually opened up, it spread to most regions of China in the mid-30s of the 20th century.
Domestic pigs and wild boars with classical swine fever can develop acute illness, elevated body temperature, systemic infection, and highly contagious disease. The main sources of infection are sick pigs and pigs carrying the virus. Infected pigs can shed the virus through the mouth, nose, urine, and feces before clinical symptoms appear. When pigs consume contaminated feed or water, the virus can infect them through the oral mucosa. Classical swine fever can occur throughout the year, and the incubation period is generally 5 days. Clinically, depending on the virulence of the strain and the clinical presentation, it is divided into 3 types: 1) acute form: signs of septicemia, organ hemorrhage or necrosis; 2) chronic form: necrotizing enteritis and paratyphoid disease; 3) mild form: no obvious skin abnormalities or skin flushing, ulceration of the ear skin, conjunctival congestion and swollen eyelids; constipation and diarrhea occur simultaneously in the group. In recent years, infections with classical swine fever virus alone have become uncommon. Clinically, classical swine fever is often a mixed infection with viruses such as PCV2 type, PRV, and PRRSV, and often presents with atypical classical swine fever symptoms, making diagnosis and prevention very difficult.
1.2 African swine fever: African swine fever originated in Africa, hence its name. It was first reported in Kenya, then spread across African countries and was introduced into other countries, causing major economic losses and harm to the global pig industry. To date, a total of 37 countries worldwide have experienced this epidemic. Because China has frequent trade with African countries and African swine fever is prevalent in neighboring Russia, the risk of its introduction into China has increased. China confirmed its first domestic case of African swine fever in 2018/8. The epidemic subsequently spread in succession to 31 provinces (autonomous regions) in China, reducing live pig production capacity, raising pork prices, and causing serious economic losses to China's pig industry.
African swine fever is an acute, febrile, highly contagious and severe infectious disease of pigs caused by African swine fever virus. Animals in the pig family are susceptible. African swine fever is transmitted mainly through contact and can circulate and spread between wild and domestic animals. After pigs are infected with African swine fever virus, they develop a persistent high fever, which can generally rise to 40–42℃; extensive redness appears locally or over the whole body; the ears become cyanotic, and vomiting blood and blood in the urine may also occur. Necropsy shows damage to the entire lymphatic system and hemorrhaging in the organs, with marked enlargement of the spleen in particular. The mortality rate of acute African swine fever infection is as high as one hundred percent. Clinical signs include lethargy, loss of appetite, high fever, and death.
1.3 Porcine reproductive and respiratory syndrome: Porcine reproductive and respiratory syndrome (PPRS) is a contagious disease of pigs caused by a virus (PPRSV). Commonly known as “blue-ear pig disease,” it can cause respiratory distress in piglets and reproductive disorders in sows. It is classified as a Category I animal disease in China. 1987 year, PPRS was first reported in North Carolina, United States, and subsequently cases were reported in European and Asian countries. In China, PPRS first broke out in 1996 year, causing losses of hundreds of millions of U.S. dollars to the pig farming industry every year.
Pigs are the only animals susceptible to PPRSV, and pigs of different breeds and at different growth stages may be infected. Fattening pigs generally show no obvious clinical symptoms after infection. PPRSV can spread directly through contact, survive for a long time in various tissues, and also be present in pigs’ secretions and excretions, with pigs continuing to shed the virus. If respiratory pathogens are present, coinfection or secondary infection is likely. PRRSV can remain latent in pigs for a long time, with an incubation period of up to 40 days. Infection can cause various clinical symptoms, most notably respiratory dysfunction, fever, and cyanosis, with the ears turning bluish-purple. Piglets may develop respiratory distress and septicemia, while growing and fattening pigs show symptoms closely associated with the respiratory system.
1.4 Porcine pseudorabies: The viral infectious disease caused by pseudorabies virus (PRV) is called porcine pseudorabies (PR). In 1902 year, researchers in Hungary first discovered PRV; it was subsequently found in other countries and regions. In 1947 year, Chinese researchers first isolated pseudorabies virus from a cat, after which numerous cases were reported across the country. In recent years, PRV infection rates have risen on many pig farms, causing serious economic losses to the pig farming industry.
Pigs of all ages can be infected with PRV, and the infection is apparent, with various clinical symptoms. After infection, sows may abort or give birth to stillborn piglets. Pigs in the suckling and fattening stages may have elevated body temperatures, with pronounced increases in rectal and oral temperatures. They may experience varying degrees of respiratory distress, as well as neurological disorders such as circling and irregular walking. Fattening pigs have particularly severe respiratory distress, and secondary mixed infections with other pathogens are also common, causing respiratory symptoms.
1.5 Porcine epidemic diarrhea: Porcine epidemic diarrhea (PED) is caused by porcine epidemic diarrhea virus (PEDV). It is characterized by acute onset and highly contagious transmission. In 1971, after PED was first identified by researchers in the United Kingdom, its presence was subsequently confirmed in several other European countries and many countries such as Japan. Between 1973 and 1984, PED occurred in China, and its presence in China was confirmed through testing. In recent years, PED outbreaks have become increasingly frequent. In 2013, PED began to break out in the United States and quickly spread to countries including Canada and Mexico. The cumulative number of piglet deaths in this outbreak exceeded 700 ten thousand. Currently, PED outbreaks are also becoming increasingly severe in countries including Italy, Germany, South Korea, Japan, and Vietnam. In 2010, a PEDV variant emerged in China, causing PED to occur and spread in multiple regions of the country. PED has now become one of the important swine diseases affecting China’s pig farming industry.
Pigs of all ages can be infected with PEDV. The case fatality rate is relatively high among suckling piglets. The main clinical signs in affected pigs are watery diarrhea and vomiting, accompanied by anorexia and depression. Body temperature is generally normal, although a small proportion of affected pigs have an elevated temperature of 1 to 2°C and pass loose, foul-smelling feces. Affected pigs have reduced appetite, severe dehydration, and rapid weight loss. Generally, dehydration and acidosis caused by passing watery feces lead to death. Fattening pigs and sows have lower case fatality rates, but may show mild signs such as diarrhea, vomiting, and loss of appetite.
1.6 Glässer’s disease: Glässer’s disease is a contagious disease caused by bacteria. Nursery pigs aged 2 weeks to 4 months, as well as growing and fattening pigs, are susceptible. The incidence is relatively high, posing a serious threat to their health. Viral epidemic diseases often aggravate secondary bacterial infections, and this is also the case with Glässer’s disease. Clinically, this disease often occurs alongside viral diseases such as porcine reproductive and respiratory syndrome and classical swine fever. To a significant extent, it increases piglet culling and mortality rates and reduces the growth performance of fattening pigs.
The main clinical signs of this disease are depression, delayed responses, and reduced feed intake or refusal to eat. Affected pigs show abdominal breathing and difficulty breathing; the skin in areas with little hair turns cyanotic. Their body temperature rises to 40.5–42°C, and in some cases can reach 43°C. The skin becomes red and the tips of the ears turn purple. Joints become swollen, especially the hock and carpal joints, and pigs walk slowly or limp. As the disease progresses, the body undergoes progressive wasting, and the coat becomes disheveled.
1.7 Porcine toxoplasmosis: Porcine toxoplasmosis is a zoonotic disease caused by a protozoan parasite called Toxoplasma gondii. The parasite lives inside cells and spreads through the blood to all parts of an infected animal’s body. It can be isolated from tissues, organs, and body fluids. Water, soil, feed, and infected animals can all serve as sources of infection for porcine toxoplasmosis. The disease can be transmitted orally, through the skin, or via the placenta, among other routes.
The incidence of porcine toxoplasmosis in China has reached as high as 60%, and the case fatality rate can be around 64%. Clinical data indicate that porcine toxoplasmosis is seasonal, with 5–9 being the months when the disease is most prevalent each year. The disease usually follows an acute course, with an incubation period of 3–5d; some cases last 1 weeks. Affected pigs develop a persistent high fever, with body temperature rising to 40–42℃, depression, and loss of appetite or refusal to eat. Diarrhea or constipation may also occur. In addition, affected pigs may have coughing, vomiting, deep inhalation, shallow exhalation, and sticky or purulent eye discharge. Purplish-red ecchymotic patches appear on the skin of the ears, snout, lower limbs, lower abdomen, and tail; severe cases may even develop extensive cyanosis. If the disease is severe, pigs may become unable to stand in the later stages.
II. Prevention and control of common pig diseases
2.1 Treatment and prevention and control of viral diseases
2.1.1 Ensure proper environmental disinfection: Pig farms should prioritize disinfection, disinfecting all people, vehicles, and other items entering or leaving the farm. Remove pig feces and urine promptly using harmless treatment methods. Thoroughly disinfect pig housing regularly; disinfecting 1 to 2 times per week is recommended. During seasons with severe viral infections, further reduce contact with epidemic areas.
2.1.2 Select medications for symptomatic treatment: Cephalosporin antibiotics and sulfonamides can be used to treat symptoms of bacterial infections. During production and weaning, certain medications can be added to feed. Chinese herbal medicines can also be added to feed and drinking water to prevent epidemics.
2.1.3 Develop a rational immunization program: Provided vaccine quality is ensured, administer safe and effective vaccines regularly. Large-scale pig farms can design scientifically sound immunization programs for pigs at each stage based on practical factors such as the prevalence of pig diseases on their farms, with particular emphasis on immunization against common diseases.
2.1.4 Immunization monitoring: Vaccine quality varies on the market, which can often lead to immunization failure. Therefore, large-scale pig farms should conduct immunization monitoring carefully and, if a problem is found, administer booster vaccinations promptly.
2.2 Comprehensive prevention and control of bacterial diseases: When bacterial diseases occur, healthy pigs can develop natural resistance to them. These pigs may be selected as high-quality breeding stock and used alongside a range of prevention and control measures to comprehensively prevent and control bacterial diseases.
When selecting a site for a livestock farm, follow principles such as low human traffic, a good environment, good ventilation, dry air, and ample sunlight. People should disinfect themselves before entering pig housing to prevent cross-infection. Ventilation should also be maintained; a suitable temperature can strengthen the pigs’ resistance. To prevent pathogens from spreading and being transmitted, regularly eliminate harmful pests such as rats, mosquitoes, and flies.
2.3 Prevention and control of parasitic diseases
2.3.1 Give importance to deworming
First, parasite control should be given priority. Choose an appropriate time for deworming according to parasite growth patterns (see Table 1). Before deworming, conduct a drug toxicity test, and use the drug on a large scale only after its safety has been confirmed. If deworming toxicity occurs, atropine can be used for treatment.
2.3.2 Eliminate intermediate hosts and maintain environmental hygiene: Some parasites must complete a certain stage of development inside an intermediate host before they can cause illness in pigs. Therefore, eliminating intermediate hosts can help control parasite-related disease in a timely manner. Take steps as early as possible to eliminate rats, mosquitoes, flies, and cockroaches, in order to reduce the incidence of related diseases.
Three. Summary
Over the past two years, African swine fever has ravaged the country, and the number of live pigs in stock has fallen sharply, with sow inventories declining severely. The development of China’s pig farming industry has been seriously impeded, resulting in enormous economic losses. As an important part of the pig industry, the production of growing-finishing pigs makes ensuring their healthy growth especially important to the pig farming sector as a whole. Therefore, becoming familiar with and gaining a thorough understanding of common diseases in growing-finishing pigs, improving disease prevention systems, managing every aspect of prevention and treatment, and administering vaccines on schedule can effectively reduce the incidence of disease, prevent major outbreaks, and avoid economic losses caused by disease.