The pig’s spleen is long and narrow. The head of the spleen is wider and thicker than the tail, and its length is approximately 4 times its width. It is relatively firm and dark red; its size varies depending on how much blood it contains.
According to traditional Chinese medicine, the spleen’s function is to transform and transport the five grains, serving as the source of qi and blood production. According to Western medicine, the pig’s spleen is an important regulatory organ for blood cell metabolism and the circulating blood volume. It is the body’s largest peripheral lymphoid tissue and has a powerful immune function. It responds sensitively to pathogen infections and can show various pathological changes, most commonly splenic hemorrhage, infarction, and inflammation. These changes have important diagnostic significance in veterinary clinical practice.
The spleen can show the following pathological changes during clinical disease:
(I) Enlarged spleen
As the name suggests, the first disease that comes to mind when you see this description is African swine fever. Of course, streptococcal infection and swine erysipelas can also cause splenomegaly. The spleen is typically 2-6 times larger in cases of African swine fever, whereas splenomegaly caused by other diseases is generally no more than 2 times larger. Streptococcal infection and swine erysipelas respond to antibiotic treatment, whereas African swine fever does not.
(II) Splenic congestion
Splenic venous congestion refers to an increase in the volume of venous blood within the spleen. The spleen becomes enlarged, its capsule taut and its edges blunt and rounded. It appears purplish red or dark red; the color fades when pressed by hand, and dark red blood flows from the cut surface. It is commonly seen in various acute infectious diseases, such as acute streptococcal and Salmonella infections, and eperythrozoonosis.
(III) Splenic hemorrhage
Bleeding that occurs in the spleen is called splenic hemorrhage. In splenic hemorrhage, scattered or diffuse pinpoint to sorghum-grain-sized hemorrhagic spots appear on the spleen’s surface, or hemorrhagic patches that are approximately round or irregular in shape. Splenic hemorrhage is seen in classical swine fever, toxoplasmosis, swine erysipelas, and swine pasteurellosis, among other diseases.
(four) Hemorrhagic infarction of the spleen
Hemorrhagic infarction of the spleen refers to local ischemic necrosis caused by an interruption of arterial blood supply to splenic tissue. The infarcted area is swollen and firm, with a moist cut surface; the lesion is dark red or blackish red and clearly demarcated from the surrounding tissue. Hence, it is also called a red infarct. It is seen in various acute septic infectious diseases, such as swine fever.
(Five) Acute splenitis
Acute inflammation of the spleen. Acute splenitis involves congestion, blood stasis, hemorrhage, exudation, degeneration and necrosis, as well as infiltration by inflammatory cells. The spleen is markedly enlarged, blackish-red or dark red, with a tense capsule, blunt, rounded edges, and a soft consistency. A blood-like fluid flows from the cut surface; when lightly scraped with a knife, a large amount of purplish-black, coal-tar-like splenic pulp can be scraped off. It is commonly seen in septicemic anthrax, acute swine erysipelas, acute paratyphoid, acute streptococcosis, and acute toxoplasmosis, among other conditions; hence it is also called septic spleen. Suspected anthrax cases must not be necropsied.
(six) Necrotizing splenitis
Necrotizing splenitis is an acute inflammation characterized by obvious necrosis of the splenic parenchyma without enlargement of the spleen. Its shape, color, and texture show no obvious differences from those of a normal spleen; unevenly distributed grayish-white necrotic foci may be seen. It is commonly observed in acute infectious diseases, such as pasteurellosis and swine fever.
(Seven) Splenic atrophy and sclerosis
In pigs suffering from long-term malnutrition or mycotoxin poisoning, it can cause splenic sclerosis and atrophy. The entire spleen becomes twisted and shrunken, with a hard texture, twisting into a “twisted-dough” shape. The splenic pulp is indistinct on the cut surface, and appears cloudy and necrotic.