For some pig farms, autumn and winter begin with a nightmare in the farrowing room: piglets that seem fine at birth stop nursing, vomit, and develop diarrhea the next day, then start convulsing, circling, and lying on their sides paddling their legs. They die within a day or two, and sometimes an entire litter dies. The sows fare no better: in late pregnancy, they may inexplicably abort, deliver stillborn piglets, or deliver mummified fetuses.

 

Many people first assume the piglets were “crushed,” are “weak,” or have “porcine parvovirus.” But another disease has symptoms that overlap considerably with these conditions and is also widespread in pig farms across China: pseudorabies in pigs.

 

One. First, let’s clear up a misconception: it is not “rabies.”

 

Pseudorabies in pigs is caused by Suid herpesvirus one and is a Class Two animal disease. The incubation period is generally 3–6 days.

 

It has nothing to do with rabies in humans, and humans cannot be infected. Higher primates are not susceptible to this virus. It is not a zoonotic disease, so there is no need to panic about this.

 

But it is highly virulent in other animals: cattle, sheep, cats, dogs, rats, foxes, and mink develop intense itching and agitation after infection, and almost 100% die. Therefore, dogs must not be kept on pig farms, and cats and dogs must not be allowed to enter and leave freely. This is not just a hygiene issue.

 

Pigs are its only natural host and reservoir host. Sources of infection include infected pigs showing symptoms, subclinically infected pigs, recovered pigs, wild boars, and infected rats. The virus is present in the droplets, saliva, feces, urine, blood, semen, and milk of infected pigs, and can spread through multiple routes, including the respiratory tract, digestive tract, breeding, and placenta.

 

The farrowing-room stage is the most vulnerable: if piglets become ill within 15 days of age, the mortality rate can reach 100%

 

Two. Symptoms by pig group: piglets are affected the most

 

Newborn piglets — the most severe stage

 

The disease usually develops on day 2 after birth, with deaths peaking between days 3 and 7. Initially, the eye sockets become red, the piglets keep their eyes closed and appear drowsy, vomit, have diarrhea, and develop a fever. Neurological symptoms soon follow: convulsions, opisthotonos, aimless circling, standing motionless, foaming at the mouth, and paddling movements. Some squeal, and death occurs within 1 to 2 days. In piglets under 15 days of age, the morbidity and mortality rates can reach 100%; those showing neurological symptoms almost all die. Most survivors are runts.

 

Weaned piglets

 

Morbidity rate 20%–40%, mortality rate 10%–20%; symptoms include fever, respiratory signs, a rough, disheveled coat, and stunted growth.

 

Fattening pigs

 

Mainly respiratory symptoms such as coughing and gasping; weight gain is slow, and the mortality rate is low in the absence of secondary infection.

 

Sows and boars

 

Sows may abort, deliver stillborn or weak piglets, or mummified fetuses; the abortion rate can reach around 50%. Empty and young sows often return to estrus, fail to conceive after repeated matings, or do not come into estrus. Boars may develop swollen or atrophied testicles and declining semen quality; severe cases may lose their breeding value.

 

A practical diagnostic clue: if mummified fetuses in an abortion-affected herd vary in size, this suggests infections occurring successively at different stages of pregnancy and points more toward pseudorabies; if the mummified fetuses are uniform in size, parvovirus is more likely.

 

Three. Why this disease is particularly difficult to control

 

First, it can remain “latent.” After recovering from infection, breeding pigs carry the virus for life. The virus hides in the ganglia and causes no obvious signs under normal conditions. Once stressors such as regrouping, farrowing, low temperatures, or vaccination occur, resistance declines and the virus is shed again, leading to a relapse. That is why this disease cannot be completely eradicated; it can only be managed through monitoring and culling.

 

Second, rats are accomplices. Rodents are highly susceptible to infection. They are small and range widely; once infected, they carry the virus everywhere and can rapidly spread it throughout the entire farm. Rodent control is not optional; it is essential.

 

Third, variant strains have emerged. At the end of 2011, pseudorabies field virus became prevalent from north to south in China. Newly isolated strains are more pathogenic, and the classic Bartha-K61 vaccine provides only partial protection against variant strains.

 

A figure to be wary of

 

In 2016, the Animal Disease Diagnosis Center of Huazhong Agricultural University tested 3206 pig farms and 67130 clinical serum samples nationwide. The pseudorabies gE antibody positivity rate reached 39.92% and has risen year by year. Field-virus contamination is widespread; many farms are already carrying the virus, but have not yet had an outbreak.

 

IV. Do not guess at diagnosis; rely on laboratory testing

 

The symptoms of pseudorabies are highly similar to those of classical swine fever, PRRS, porcine parvovirus, and Japanese encephalitis. It is easy to misidentify the disease based on clinical symptoms alone, so samples must be submitted for testing to confirm the diagnosis.

 

At present, the most useful test is the gE antibody ELISA. The mainstream vaccines used domestically are all gE gene-deleted vaccines. Vaccination does not produce gE antibodies; only infection with wild-type virus does. This makes it possible to distinguish “vaccine immunization” from “wild-type virus infection.” This capability is the foundation of all eradication programs.

 

Suitable samples include aborted fetuses, stillborn and mummified fetuses, the brain, tonsils, and lungs of piglets that have died of disease, and serum from the herd.

 

Late-term abortions and mummies of varying sizes are signals most easily overlooked on breeding farms

 

Five: All four prevention and control measures are essential

 

First: Vaccinate correctly, especially—do not miss intranasal vaccination.

 

Use a gE gene-deleted live vaccine (such as the Bartha-K61 strain) and a gene-deleted inactivated vaccine. Use only one type per farm; do not mix different types. Reference schedule (follow the product instructions and the plan of a licensed veterinarian):

 

· Intranasal administration to piglets aged 1–3 days: 1 doses per pig, diluted with the dedicated diluent; administer 0.5 dose into each nostril;

 

· Intramuscular injection of 1 doses in the neck at 30–45 days of age, followed by another intramuscular injection of 1 doses at 70–75 days of age; farms with high infection pressure may add one dose at around 110 days of age;

 

· Sows: immunize according to gestation stage 4 weeks before farrowing, or conduct routine immunization 3–4 times per year;

 

· Replacement gilts: immunize 45 days before breeding, with a booster after an interval of 3–4 weeks;

 

· Boars: 3–4 times per year. Do not collect semen or breed within one week after immunization.

 

Why is intranasal administration essential? This is the most distinctive measure against pseudorabies.

 

Newborn piglets have high levels of maternal antibodies, which can protect them from disease but also interfere with intramuscular vaccines, reducing their effectiveness. Intranasal administration triggers local mucosal immunity, establishing a defense at the “entry point” in the nasal cavity—the virus’s first point of entry—and securing the position before the field virus arrives. When administering the drops, tilt the piglet’s head slightly upward so the liquid actually enters the nasal cavity rather than running straight out after spraying.

 

Second: Rodent control—take it seriously. Carry out rodent control regularly. Place bait stations in a line along the walls of pig houses, around feed rooms, and around the perimeter of the site; replenish and replace the bait regularly and keep records. Clear weeds and debris outside the buildings so rats have nowhere to hide. This measure costs little and delivers a very high return.

 

Third: Keep non-porcine animals out. Do not keep dogs or cats on the farm, and do not allow stray cats or dogs into the production area. Take extra care with biosecurity if there are fox or mink farms nearby.

 

Fourth: Disinfection and sourcing replacement animals. Pseudorabies virus is enveloped and is susceptible to lipid solvents and commonly used disinfectants. Povidone-iodine, quaternary ammonium compounds, and chlorine-based disinfectants are all effective, making it much easier to deal with than foot-and-mouth disease. Thoroughly clean and disinfect farrowing rooms and nursery barns, and let them dry while empty before bringing pigs in. Replacement animals must come from a gE-negative farm. Check the test reports, then quarantine and monitor them on arrival; only after they pass testing should they be mixed with the herd.

 

Place rodent bait stations in a line along the base of the wall: rodents are the accomplices that spread pseudorabies the fastest

 

Six. How should a positive farm proceed with eradication?

 

For a herd that is already infected, the approach is clear: testing—culling—monitoring.

 

Collect blood samples throughout the herd for gE antibody testing, and gradually cull positive pigs, especially breeding pigs. At the same time, strengthen vaccination to suppress clinical disease, and strictly control rodents and maintain biosecurity to prevent reintroduction. Then retest quarterly or every six months to gradually reduce the positive rate. According to the technical specifications, a breeding farm may be deemed to have achieved eradication if random testing for gE antibodies is negative in all pigs for two consecutive years and there are no clinical cases.

 

This road is not fast, but it is workable. A number of domestic breeding pig farms have already completed it.

 

Seven, four areas that are easy to misjudge

 

First, “There are no dogs or cats on the pig farm, so it won’t get infected”—rats can still spread it, and wild boars and introduced animals are also routes of entry.

 

Second, “Once the vaccine has been administered, everything is taken care of”—a variant strain, interference from maternal antibodies, or improper intranasal administration: any one of these can break through the defenses.

 

Third: “Piglets are crushed, weak, or hypoglycemic”—if the whole litter develops neurological symptoms, paddles convulsively, and then dies, first consider pseudorabies.

 

Fourth: “Sow abortions are caused by parvovirus or Japanese encephalitis”—check whether the mummies are all the same size, then consider whether the piglets show neurological symptoms; prioritize testing to rule out pseudorabies.

 

The autumn and winter farrowing period is the most vulnerable time of the year for a pig farm. If you get intranasal administration right, reduce the rat population, and gradually cull breeding pigs carrying the virus, you can gradually recover the losses caused by pseudorabies.