Originally from: lina
                        
New and Old Players Plague Producers

by Kurt D. Rossow, DVM, Minnesota Veterinary
Diagnostic Laboratory, University of Minnesota

Bacterial diarrhea (enteritis) in swine continues to
be a daily challenge for pork producers and
veterinarians in treating affected pigs. Some bacteria
causing diarrhea have been consistent problems over
the years, while other types have declined in case
numbers only to be replaced by newly identified
bacteria.

Reviewed in this article are some of the common
bacteria currently and historically associated with
diarrhea in pigs. The frequency of the different types
of bacteria associated with diarrhea in pigs may vary
by site and by production system.

General Diagnostic Tips
When trying to identify the bacteria causing diarrhea,
it is important to select pigs in the early stages of
the disease that have not been treated with
antibiotics. Testing pigs in the later stages of
diarrhea, or pigs that have been treated with
antibiotics, may yield negative or inappropriate
results. Most diagnostic efforts involve testing for
multiple agents.

The types of bacteria that produce diarrhea are
commonly age associated. For pigs still in farrowing
crates, Clostridium perfringens Type A and Escherichia
colibacillosis (E. coli) represent the more common
agents. Clostridium difficile and Clostridium
perfringens Type C are identified less often.

Clostridium perfringens
Clostridium perfringens Type A represents one of many
types of Clostridium perfringens causing diarrhea in
young animals (Figure 1). Clostridium perfringens
Types A through E are differentiated by the type(s) of
toxins (specifically one or more of four exotoxins)
each produces. Pigs most likely to get this diarrhea
are infected with Clostridium perfringens by oral
exposure to feces.

Clostridium perfringens isolates are currently typed
by polymerase chain reaction (PCR) technique to
identify the gene responsible for toxin production.
Many of the Clostridium perfringens Type A isolates
associated with diarrhea are also positive for the
beta-2 toxin gene.

Clostridium perfringens Type A is commonly found in
most farms. The spore form of the organism easily
survives in the environment.

Diarrhea most commonly occurs within the first three
days of life and may last for up to five days.
Clostridium perfringens Type A infection results in a
watery-to-pasty, white-to-yellow diarrhea. Pigs will
lose some body condition and growth slows. The
affected intestine may look normal or slightly
thickened.

The number of pigs affected may be high, but death
from Clostridium perfringens Type A alone is
considered to be low.

Clostridium perfringens can be isolated from the small
intestine of affected pigs by anaerobic culture.
Histopathologic lesions (structural tissue changes
viewable with a microscope) also help define it as a
causative agent.

E. coli in Nursing Pigs
E. coli diarrhea in nursing pigs usually occurs within
the first seven days of life and, even more commonly,
between three hours and four days of age. Pigs from
gilt litters are more commonly affected due to less
colostral antibody protection.

Other factors that may influence the development and
severity of E. coli diarrhea in young pigs include
dirty crates at farrowing and low air temperature.

Most E. coli attach to the surface of the small
intestine by fimbriae (a filamentous bacterial cell
wall appendage that binds to the surface of the pig's
small intestinal cells). The types of receptors vary
and have been given different designations such as
K99, F41 and 987P. The E. coli attach to small
intestine cells and produce toxins, causing fluid loss
into the intestine and the resultant diarrhea.

Clinical signs usually include severe watery diarrhea,
dehydration, sunken eyes, lethargy and death, if left
untreated. The affected intestine may be
fluid-distended and thin-walled or empty.

The E. coli that is infecting the pigs can be cultured
from small intestine as well as attachment to
intestinal cells identified by histopathology. The E.
coli can be further typed by PCR characterization of
the fimbrial (pilus) and toxin genes.

Clostridium difficile
Clostridium difficile is one of the more recently
recognized bacteria associated with baby pig diarrhea.
Like Clostridium perfringens, Clostridium difficile is
also commonly found in the environment.

Clostridium difficile has been associated with
diarrhea in pigs up to 10 days old. Affected pigs show
a mildly distended abdomen, with or without diarrhea;
lethargy; and temporary loss of appetite. The affected
colon is commonly edematous (thickened by clear
fluid). The number of sick pigs may be high, but
mortality is generally low.

As with Clostridium difficile infection in other
species, development of infection may be linked to
prior oral antibiotic treatment that changes the
normal intestinal bacterial population.

Diagnosis of Clostridium difficile infection is
usually evident by typical lesions in the colon and
identification of toxin in colon contents. Clostridium
difficile culture requires special conditions.

Postweaning E. coli Diarrhea
Postweaning E. coli diarrhea is usually associated
with two groups of bacteria designated by their
fimbrial type, K88 and F18. As with E. coli infection
in preweaned pigs, the E. coli bacteria binds to
intestinal cells and secretes toxins, resulting in
fluid loss(Figure 2).

In addition, some postweaning E. coli may secrete a
toxin known as shiga-like toxin, which is responsible
for the development of central nervous system signs
such as staggering, uncoordination, poor balance,
paddling and convulsions.

Both K88 and F18 E. coli may exist and cause clinical
disease in the same group of pigs. In some cases, K88
E. coli infections precede F18 infections.

Postweaning E. coli infections can be distinguished by
a variety of clinical signs, including watery
red/bloody diarrhea; loss of appetite; central nervous
system signs; and sudden, unexpected death. Pig
eyelids may appear remarkably swollen and intestinal
contents are liquid. The gastrointestinal tract in
some pigs may be completely empty at death.

The type of E. coli involved in the diarrhea can be
further characterized by PCR typing. This process can
identify the genes in the bacteria that code for the
fimbrial type as well as the genes responsible for
toxin production.

It is important to properly identify the E. coli
responsible for disease in order to develop
appropriate treatment and control plans.

Salmonella
There are many types of salmonella that can infect
pigs; however, the two types associated with clinical
diarrhea problems in pigs are Salmonella typhimurium
and, less commonly, Salmonella cholerasuis.

Other types of salmonella may be implicated in
short-lived episodes of diarrhea, but generally don't
have the serious implications of S. typhimurium and
cholerasuis infections. Some salmonella infections in
pigs are asymptomatic.

Salmonella diarrhea usually affects pigs from
postweaning to 4 or 5 months of age; however, it is
occasionally seen in adult swine.

Salmonella typhimurium infection results from contact
with infected pigs or a contaminated environment. Once
contaminated, some facilities may remain the source of
infection for new groups of pigs.

Pigs infected with Salmonella typhimurium may be
subclinically (inapparent) infected or develop
diarrhea. The bacteria infect both the small and large
intestine, inducing fluid loss that results in
diarrhea, and damaging the intestinal surface.

At first, affected pigs will have a watery diarrhea
that may contain flecks of blood and mucous. Pigs are
also febrile (feverish), dehydrated and show signs of
weight loss. The diarrhea quickly spreads to other
pigs in the pen and is easily tracked to other
locations. Pigs may have recurring episodes of
diarrhea over several weeks. The colon and intestine
in affected pigs may be thick-walled with an ulcerated
surface lined by small to large pieces of debris.

Salmonella cholerasuis infection may also result in
diarrhea and intestinal damage if the pigs survive the
severe, initial septicemic (invasion of the
bloodstream by infective organisms) stage of the
disease.

Salmonella diarrhea can be diagnosed by culture and
examination of tissues by histopathology.

Porcine Proliferative Enteritis
Porcine proliferative enteritis (PPE) caused by
Lawsonia intracellularis is an intestinal disease of
swine occurring in pigs from 6 to 20 weeks of age. But
it also occurs in adult hogs.

Infection can take two diverse routes. It can result
in severe intestinal disease and death, or occur as an
inapparent infection with disease presented only as
decreased performance (Figure 3).

The bacteria are shed in the feces of all clinically
infected pigs, but also in pigs with inapparent
infections. Transmission between pigs occurs through
direct contact with feces from infected pigs.
Ingestion of the bacteria results in infection of
small and large intestinal cells, and clinical
diarrhea usually starts 2–3 weeks later. Diarrhea may
occur in less than half of the infected animals,
however.

Clinical disease may take a chronic form or an acute,
hemorrhagic form. In the chronic disease form, pigs
may have a soft-gray/brown stool that alternates with
normally-formed stools on other days. Appetite usually
decreases and pigs become thin. There may be size
variation within the group. Pigs will normally recover
in four to 10 weeks.

Both the large and small intestine may be affected,
but changes are usually more severe in the small
intestine. The intestinal wall appears slightly to
markedly thicker and the surface may be lined by a
thick layer of yellow/white debris.

The acute, hemorrhagic form of PPE or ileitis is more
common in young adults and is characterized clinically
by loose-to-formed black (bloody) feces and a pale
body color (due to blood loss) (Figure 4). Some pigs
die suddenly without showing any signs of diarrhea or
blood loss in the stool. The intestine in this form of
the disease is usually thick-walled (Figure 5) and the
cavity contains blood or blood clots.

Diagnosis of PPE by histopathology is usually
straightforward in pigs with obvious intestinal
changes. The bacteria can be demonstrated with special
stains under the microscope or by PCR. However, the
bacteria are very difficult to grow; culture is not
even attempted in routine testing.

Subclinical forms of the disease can be even more
challenging to diagnose. The bacteria can be
identified in the feces of clinically affected pigs by
PCR but not in all subclinical infections. Serologic
testing is available, but the number of pigs
seroconverting in a group may move slowly, with only
5% to 50% positive.

Swine Dysentery (Brachyspira hyodysenteriae)
Swine dysentery, primarily a disease of growing and
finishing pigs, causes severe catarrhal (abundant
mucous) and hemorrhagic colitis. The number of cases
of swine dysentery has decreased dramatically, with
success for control and elimination credited to
antibiotics and modern production practices.

Transmission of the bacteria is through fecal shedding
by infected pigs to susceptible pigs. Contaminated pit
waste, mice, birds and dogs are other potential
sources of infection and disease spread.

Disease usually spreads slowly within a herd. Affected
animals develop diarrhea, dehydration and weight loss,
and death losses may be as high as 50%. The bacteria
grow in the colon (not the small intestine), producing
toxins that result in damage to the colon.

Diarrhea is associated with malabsorption rather than
fluid loss. The diarrhea associated with swine
dysentery is initially a watery, yellow diarrhea that
progresses to large amounts of blood-flecked,
mucous-filled stool. At necropsy, the colon wall is
markedly thickened and the surface is covered by a
thick layer of mucous, blood and cell debris. The
lumen or organ cavity may be filled with blood and
cell debris forming luminal casts.

Diagnosis is by histopathology, culture and isolate
verification using PCR analysis.

Porcine Intestinal Spirochetosis (Brachyspira
pilisicoli)
Brachyspira pilisicoli is related to, but distinct
from, the causative agent of swine dysentery. The
bacteria are identified with a syndrome of mild
diarrhea caused by a mild colitis. Production losses
are associated with treatment costs and a loss of body
condition. Mortality is very low.

Infection is thought to occur by the fecal-to-oral
route. The incubation period may be up to 20 days and
infected pigs develop a self-limiting, soft-to-watery
diarrhea that lasts from two to 14 days. Colon and
cecum (opening to the large intestine) in affected
pigs appear thin-walled and filled with soft, green
feces.

Diagnosis is by culture, histopathology or
immunohistochemistry and PCR-based typing.

Conclusion
The bacteria causing diarrhea in pigs will continue to
be recurring problems for pigs, producers and
veterinarians. In some cases, antibiotics are no
longer an option due to resistant bacteria. Sanitation
plays an important part in controlling intestinal
diseases of swine.

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