Equine Neonatal Septicemia
Septicemia is a systemic disease associated with the presence and persistence of bacteria and their toxins in the blood eventually leading to septic shock. The word septicemia literally means bacterial invasion of the blood, and it arises from a seat of infection somewhere in the body. Once a local infection opens the door for bacteria to enter the bloodstream, they travel throughout the body. This widens the circle of infection and tissue damage.
For instance, infection of the navel (umbilicus) facilitates the movement of bacteria into the blood, which then relocate to the lung causing pneumonia. Bacteria also release toxins (chemical poisons) that cause further complications, on their own. Thus, septicemia is a complex process initiated by bacterial infection and perpetuated by the spread of those bacteria and toxins to cause dysfunction and even failure of multiple organs, including the kidneys, liver, joints and lungs.
Septicemia is an important disease of neonatal (less than 14 days of age) foals. Thirty-three percent of neonatal deaths can be attributed to septicemia. In one study of 160 neonatal foals hospitalized for various reasons, septicemia was the second most common problem diagnosed. It was surpassed only by the problem of inadequate transfer of maternal antibodies from the dam's colostrum.
The foal can be exposed to bacteria in many ways. The exposure may take place while the foal is still in the mare's uterus. This is generally a consequence of the mare developing an infection of the placenta near the end of her pregnancy. Infection can also come through the blood of the mare to the fetus if the mare is severely ill (e.g. with septicemia) before birth or parturition. The foal can also get infected when exiting the birth canal. Infections that occur after the foal is born are commonly promoted by failure of the foal to get antibodies from the mare. This is called failure of passive transfer. The bacteria gain entry to the foal by inhalation, ingestion, and contamination of the umbilical stump and through wounds.
The clinical signs of septicemia are variable. They range the full spectrum from mild depression to shock and death. It is often difficult to identify the foal in the beginning of the illness. Early identification is essential in the prevention of the progression of the problem into irreversible shock. Foals usually start out with mild to moderate depression, decreased suckling frequency, and sleepiness, loss of energy, or weakness.
Because the bacteria are in the bloodstream, they can travel and settle in various organ systems causing local system infection or failure. One foal may have more than one system affected at the same time. Some of the body systems that are most affected include the following:
- Respiratory system. Pneumonia is one of the most common sites of infection with approximately 50 percent of the septic foals presenting with respiratory signs.
- Gastrointestinal system. Enteritis/diarrhea is the second most common manifestation of sepsis.
- Musculoskeletal system. Bone (osteomyelitis) and joint infection (septic arthritis) occur when the bacteria invade the growth plate of the bone or the lining of the joint (synovial membrane).
- Nervous system. Meningitis (infection of the meninges of the brain) has a very poor prognosis for life.
- Umbilical structures. Infections of the umbilical structures are often not apparent from the exterior of the body.
What to Watch For
It is not difficult to diagnose the foal that is in septic shock. These young animals are generally severely depressed to comatose. Their legs are cold and it is difficult to find a pulse. The challenge comes in diagnosing foals that are only beginning to show subtle signs of depression. Early signs include:
- Signs of depression
- Foal lying down more than normal
- Mare's udder is distended with milk
To recognize the early stages of sepsis, your veterinarian will attempt to get clues from a thorough perinatal history, that period shortly before and after birth, and a physical examination. This information is supplemented with some blood work, which will include a complete blood count, a serum immunoglobulin level and blood glucose. Additional blood work that is helpful if available is a blood culture, an arterial blood gas analysis, serum electrolytes and chest radiographs.
Once septicemia is suspected then treatment should start immediately. Care can be quite intensive and may require that the foal be sent to a hospital that has the ability to monitor the foal 24 hours a day. The general treatment of a septic foal should include:
- Immunologic support. Foals with failure of passive transfer of maternal antibodies need to be provided with some protective antibodies. This is usually accomplished through a plasma transfusion.
- Antibiotic support. Antibiotics are used to help kill the bacteria that are causing the signs of septicemia. Any number of bacteria in the foal's environment can cause septicemia. Because you can't delay treatment until you identify causative bacteria, your veterinarian will place the foal on an antibiotic or combination of antibiotics that will kill the majority of bacteria involved.
- Shock treatment. Foals that are already in shock will need intravenous fluids to support their circulation.
- Nutritional support. Many septic foals are too depressed and sick to eat. Your veterinarian may need to feed the foal hourly or every two hours through a nasogastric tube.
Home Care and Prevention
Home care begins with prevention of septicemia. Because the largest risk factor for the development of septicemia is failure of passive transfer, owners should be extremely observant of the late pregnant mares. Any leakage of milk from the udder before the foal is born is cause for concern. High quality colostrum gives the newborn foal the tools to fight most normal bacterial contamination at birth.
It is important for owners to be present at the time of foaling as well. The mare may have excellent colostrum, but if the foal does not stand and nurse within three hours of foaling, the bacteria will have a chance of establishing residence before the foal has a chance to build his defenses. At the time of foaling, owners should disinfect the foal's umbilicus. The umbilicus can be a portal of entry to the environmental bacteria. Because ingestion is also a way that bacteria can invade a foal's systems, cleaning of the mare's udder and hind legs with a light disinfectant or soap may reduce the number of bacteria that the foal's are exposed to at birth.
Next to prevention, early recognition of septicemia is the next best thing that owners can do. The first sign of a bacterial infection in a foal may be that he is not as active as other foals. You may see him lying down more than he should. The mare's udder may be distended indicating that he is not drinking as much milk as he should. If you have any concerns about the health or behavior of the foal, insist that your veterinarian check the foal out as soon as possible. Septicemia is an emergency.
The most common cause of equine neonatal deaths is bacterial infection. Bacterial infection can be local such as an infected wound or it can be widespread throughout the body. When it is widespread in the body is usually called septicemia or sepsis and is generally spread through the bloodstream. Some bacteria also release toxins into the blood that can lead to a deterioration of the foal's condition. The causative bacteria are bacteria normally found in the environment. These same bacteria will not cause a problem if the foal receives good quality colostrum from the mare within three hours of birth. It is the unprotected foal that is at highest risk for septicemia.
- Failure of passive transfer of colostral antibodies
- Unhygienic environment
- Severe exposure to cold
- Advanced age of the dam
- Pre-maturity (born too soon)
- Post-maturity (born late, prolonged pregnancy)
- Poor health of the dam
- Presence of foreign bacteria
The bacteria can enter the foal's body through several portals. Exposure may take place while the foal is still in the mare's uterus. This is generally a consequence of the mare developing a placentitis (infection of the placenta) near the end of her pregnancy. Infection can also come through the blood of the mare to the fetus if the mare is severely ill before parturition (birth).
Infections that occur after the foal is born are commonly associated with the problem of failure of passive transfer of maternal antibodies to the foal. The bacteria can gain entry to the foal by inhalation of infective particles, such as dust, or ingestion – in the foal's attempt to find the mare's udder, it suckles on the walls of the stall, buckets, and other parts of the mare's body. Unsanitary conditions will increase the number of bacteria that the foal ingests. Remember the foal is ingesting these bacteria before he has ingested his colostrum, and the same mechanism that facilitates the foal's absorption of the antibodies from the intestinal tract will facilitate the absorption of bacteria.
An infection of the umbilical structures can lead to the circulation of bacteria in the bloodstream and hence septicemia. These structures include two umbilical arteries, one umbilical vein and the remnant of the connection between the bladder and the allantoic sac in the fetus. The bacteria can infect one or all of these structures, forming an abscess. This type of infection is not visible on the external body wall. An ultrasound examination of the structures is needed to discover a problem here.
The most common bacteria isolated from septic foals is Eshericha coli (E. coli). Others that may be involved include Klebiella, Enterobacter, Actinobacillus, Salmonella and Streptococcus. Approximately half of the foals with sepsis are infected by a single organism and half are infected with multiple organisms. Some of the bacteria mentioned above contain a toxin in their cell walls that is called endotoxin. When endotoxin is released into the blood stream it causes the release of other chemicals in the body called cytokines. These cytokines cause the symptoms of depression, anorexia and fever.
The clinical signs of sepsis vary depending on the amount of colostrum the foal has received, the number and type of causative bacteria, and whether the foal was infected in the uterus or after birth. The earliest sign may be that the foal is slightly depressed or doesn't act as lively as other foals. This progresses to a foal that is not eating.
The severe signs may include
- Increased respiratory rate and effort
- Swollen joints
The reason that so many body systems can be involved either singularly or in multiples in the same foal, is that the bacteria are carried by the blood stream. This allows infection of any body system where blood flows, which means everywhere. The final stage of sepsis is shock, where the body is overwhelmed. Blood pressure drops, gums become either bright red or pale, the foals are unconscious and finally they go into cardiac and respiratory arrest.
It is not difficult to diagnose the foal that is in septic shock. The challenge comes in diagnosing foals that are only beginning to show subtle signs of depression. Because there are other causes of depression in foals, and septicemia requires special treatments, it is important to distinguish septicemia.
Dr. Anne Korterba, University of Florida, developed a scoring system in the early 1980s. This is a tool that veterinarians use to assess the likelihood of a foal being septic. Information needed for using this scoring tool includes a good perinatal history, physical examination findings and some blood work, which includes a complete blood count, a serum immunoglobulin level and blood glucose. The common results from these tests in septic foals are a low white blood cell count, a low immunoglobulin level (less than 400 mg/dl) and low blood glucose. The foal receives a numeric score for these abnormalities. Scores that are over 11 are highly suspicious of being septic. This system allows early detection of septicemia before foals develop irreversible problems.
Other diagnostic procedures include:
- Chest radiographs. X-rays are important in determining the degree of respiratory compromise. Listening to the lungs with a stethoscope is helpful, but it can be misleading in come cases of pneumonia. If an area of the lung is completely filled with fluid, there will be no abnormal lung sounds heard. Radiographs, however, will show you this area.
- Arterial blood gas analysis. It is important to know whether the foal is able to transfer oxygen from the air into its blood. If the blood oxygen is low then the foal probably has pneumonia. If you combine this finding with abnormal chest radiographs, you have a fairly good approximation of the degree of respiratory involvement. It also helps you determine your therapy. A foal with a low oxygen would benefit from oxygen administration.
- Joint radiographs. A bone infection may not be evident in the beginning of the disease so it is important to repeat this procedure in 4 to 5 days if the foal does not respond to therapy. If bone infection is evident then the prognosis is worse.
- Joint fluid analysis and culture. The fluid analysis of the foal with septic arthritis will have an increase number of white blood cells and increased protein. It will tend to be more watery than normal joint fluid. Cultures of septic joints is not always rewarding. For some reason it is more difficult to grow bacteria from joint fluid. A positive culture is probably obtained about 1/3 of the time.
- Blood cultures. Blood cultures do not always show a positive result, especially if the foal has already received antibiotic prior to the culture. The cultures take several days before their results can be reported, so they are not very useful in the beginning of the disease. They are most helpful in cases where the foal does not respond to initial antibiotic therapy. It identifies the causative agent and gives information about which antibiotic should be used.
Once septicemia is suspected, treatment should start immediately. The general treatment of a septic foal is outlined below. Depending on which body system is affected, there is system specific therapy that needs to be started. Care can be quite intensive and may require that the foal be admitted to a hospital that has the ability to monitor the foal 24 hours a day.
- Immunologic support. If a foal is older than 12 hours old, he may not be able to absorb the amount of colostrum needed to protect him from infection. Because of this the next best way to provide foals with antibodies is through a plasma transfusion. The amount of plasma necessary depends on the level of immunoglobulin present in the foal's blood. A foal with less than 200 mg/dl of immunoglobulin has received no colostrum and may required two or more units of equine plasma.
- Antibiotic support. Antibiotics are used to help kill bacteria. Because you can't delay treatment until you identify the causative bacteria, your veterinarian will place the foal on an antibiotic or combination of antibiotics that will kill the majority of bacteria involved. A common combination of antibiotics used in septic foals is amikacin and penicillin/ampicillin. Most E. coli and Streptococcus infections are sensitive to this combination.
- Shock treatment. Foals in shock have a lower blood pressure, which in turn causes decreased blood flow to the different organ systems. The kidneys are particularly affected. Intravenous fluids help to support their circulation. Foals less than 24 hours old often have a dangerously low blood sugar, and it is essential to correct this as soon as it is recognized by adding glucose to the fluids. The foal's blood may also become acidotic. Since there is a very narrow range of acidosis within which an animal can live, sodium bicarbonate can be added to the fluids to correct this abnormality.
- Nutritional support. Septicemia and endotoxemia may cause foals to be anorexic. A foal needs between 6,000 and 8,000 kcals/day to support healing and growth. Because many sick foals will not or cannot suckle from their dam, your veterinarian will need to feed the foal through other methods, such as intubation or intravenous fluids. If the foal does not have diarrhea it is best to feed it with an indwelling tube from his nose to his stomach. For the first week of life the foal may need to be fed hourly or every other hour. Mare's milk or a commercial milk substitute can be used. If the foal has a gastrointestinal problem then intravenous feeding may be needed.
System Specific Therapy
- Respiratory support. Septic foals with bacterial pneumonia have the lowest survival rate of all septic foals. Intensive respiratory physiotherapy is important in keeping the foal alive until the antibiotic and immunologic assistance has a chance to work. The amount of therapy depends on the severity of the respiratory compromise. It may consist of intranasal oxygen or mechanical ventilation.
- Septic arthritis/osteomyelitis. Infection in or around a joint causes inflammation and joint swelling. The inflammation brings in enzymes that can destroy the cartilage that cushions that joint. It is important to tap into the joint fluid and flush the enzymes out to prevent further damage. Often this has to be done several times and may require anesthesia.
- Meningitis. If the bacterial infection enters the central nervous system, the prognosis for survival is poor. Anticonvulsant drugs, such as Valium, maybe needed to control seizures. Antibiotic therapy would change to include an antibiotic that penetrates the meninges better that amikacin.
- Eyes. Two different problems can be present in the eyes of the septic foal – uveitis and corneal ulceration. Uveitis is manifested as inflammation and/or pus in the front part of the eye. Corneal ulceration is usually secondary to the foal scratching his eye during his recumbency or from an inverting of the lower eyelid (entropion) when the foal is dehydrated and the eye ball sinks back into his socket. Treatment involves antibiotic and anti-inflammatory eye ointments and perhaps a small suture placement to correct the entropion.
- Umbilical infections. Umbilical remnant infections that have been diagnosed by utlrasonography should be removed surgically as soon as the foal's condition is stable enough to permit surgery. The foal is anesthetized, and the umbilical structures are carefully dissected. Any areas of discoloration or swelling are removed and cultured.
Before 1980, equine neonatal intensive care did not exist as a field of study. The philosophy of neonatal care was "survival of the fittest." It was generally accepted that sick foals would not grow up to be useful adults. The first decade of equine neonatal intensive care was characterized by a steep learning curve for the veterinarian. The increasing knowledge base and case management skills improved the prognosis of the septic foal from 25 percent to 75 percent survival that we see today.
Follow-up surveys of the survivors of neonatal septicemia demonstrate that the long-term prognosis for septic foals is often good. Owners have indicated that their foals become healthy adults that are comparable to their stablemates in weight, height, soundness and athletic ability. Foals that would have died 20 years ago, go on to become successful race horses and breeding animals. Currently ongoing studies exist that aim to determine the fate of foals surviving neonatal intensive care.
Although our increased knowledge in the treatment of neonatal sepsis has brought about these improved survival rates, sepsis is still one of the most difficult problems we face in neonatal medicine. Owners often feel like they are on an emotional roller coaster because the foal's condition can change rapidly. One day the foal has diarrhea, the next day he has developed infected joints and the third day he needs surgery to have his umbilicus removed.
Each of these problems must be taken care of one at a time. Care remains costly and labor intensive and can range from $2,500 to $5,000 for a 5 day stay in an intensive care facility. The very sick foal may have an attendant with them 24 hours a day. It is important the veterinarian, hospital staff and owner be committed to the care of the septic foal if the outcome is to be favorable.