Overview of Toxoplasmosis in Dogs
Toxoplasmosis is an infectious disease caused by a single-celled parasite called Toxoplasma gondii. Toxoplasmosis can occur in both cats and dogs. This disease is zoonotic, which means it is transmissible to humans, and pregnant women especially must be careful.
Animals that are fed raw or incompletely cooked meat are at higher risk of developing toxoplasmosis, as well as animals that are immunosuppressed.
Dogs usually contract the disease by the following means:
Transplacental transmission – The organism is ingested by a pregnant animal, multiplies in the placenta and then infects the developing fetus.
Ingestion of the organism when they feed on the tissues of infected birds and rodents.
Ingestion of food or water contaminated with infected feces.
Transfusion of infected blood (rare).
What to Watch For
The signs of toxoplasmosis in pets are nonspecific, and most dogs show no signs of infection. These signs may include fever, loss of appetite and depression. Further signs may occur, but that depends on where the infection occurs; toxoplasmosis can affect any organ system but primarily affects the lungs, the central nervous system (brain) and the eyes.
Central nervous system signs may include depression, a head tilt, partial or total blindness, seizures and death.
Respiratory signs may include fever, cough, and increased respiratory rate and effort.
Uveitis (inflammation of the interior of the eye) may cause excessive blinking (blepharospasm), squinting, and sensitivity to light (photophobia).
Other signs that may be observed are ascites (accumulation of fluid in the abdomen), jaundice, hepatomegaly (liver enlargement), muscle pain, loss of appetite, and weight loss.
Diagnosis of Toxoplasmosis in Dogs
The best method to diagnose toxoplasmosis is measurement of antibodies to the organism. Your veterinarian may also do other diagnostic tests, such as:
Complete blood count (CBC)
Ocular (eye) examination
IgG and IgM antibody testing (titers)
ELISA test (antigen test)
Cerebrospinal fluid analysis (CSF analysis)
Analysis of pleural (chest) or peritoneal (abdominal) fluid
Treatment of Toxoplasmosis in Dogs
Antibiotics such as clindamycin, trimethoprim-sulfonamide, or sulfonamides combined with pyrimethamine
Anticonvulsants for seizures
Intravenous (IV) fluids for debilitated animals
Home Care and Prevention
At home care consists of administering any medications prescribed by your veterinarian.
Feed only dry, canned or cooked food. Do not feed uncooked meat, entrails or bones as these tissues may contain toxoplasma cysts. Secure trash containers to prevent garbage scavenging and remove carcasses of rodents or birds before they are consumed.
In-depth Information on Toxoplasmosis in Dogs
Related Symptoms or Diseases
Neospora caninum is an infectious disease caused by a protozoal organism, which is similar to toxoplasma gondii. Neosporosis produces symptoms that are identical to those of toxoplasmosis and the diagnosis is made on the basis of a negative titer for toxoplasma and a positive titer for neospora.
Acute viral gastroenteritis results in loss of appetite, nausea, vomiting, diarrhea and a low white blood cell count. The most common viruses causing these symptoms are parvovirus and coronavirus. These viruses usually affect young, unvaccinated dogs and may be differentiated from toxoplasmosis on the basis of negative titers for toxoplasmosis.
Canine distemper virus usually affects young, unvaccinated dogs and results in signs of gastroenteritis (vomiting and diarrhea), respiratory disease (increased respiratory rate and effort) and central nervous system disease (behavior changes, seizures, coma). Canine distemper virus is very difficult to diagnose and would be differentiated from toxoplasmosis on the basis of the pet’s age, medical history and toxoplasmosis titers.
Protothecosis is a green algae that causes systemic infection in dogs. This organism is found in sewage, animal waste, and contaminated soil and food. Protothecosis causes loss of appetite, weight loss, diarrhea, depression, incoordination, paralysis, and ocular lesions. This disease may be distinguished from toxoplasmosis on the basis of toxoplasma titers.
In-depth Information on Diagnosis
The diagnosis of toxoplasmosis can be very difficult. In addition to obtaining a complete medical history (including your pet’s travel history) and performing a complete physical examination, your veterinarian will likely perform many of the following diagnostic tests.
A complete blood count (CBC) is done to assess whether the pet is anemic (low red blood cell count) and to assess the white blood cell count. Pets with toxoplasmosis are commonly anemic however the white blood cell count often remains unchanged.
A serum chemistry profile allows your veterinarian to evaluate the internal organs such as the liver, pancreas, and kidneys. Because toxoplasmosis often causes elevations in liver enzymes and total bilirubin (causing jaundice) this test is essential to evaluate involvement of the liver. Additionally, elevations in blood sugar, total protein levels, and globulin levels may be present.
Examination of a fecal (stool) sample may be performed to look for toxoplasma oocysts (one of the life cycle stages of toxoplasma). Because infected dogs shed oocysts intermittently, a fecal sample may be negative despite serious infection. Thus, a negative fecal sample does not rule out toxoplasmosis.
An ocular (eye) examination should be part of the physical examination performed by your veterinarian to look for evidence of uveitis (inflammation of the interior of the eye), hemorrhage or fundic (back of the eye) lesions that are commonly present with toxoplasmosis. The finding of these lesions does not definitively diagnose toxoplasmosis but it does raise the index of suspicion for the disease and should prompt your veterinarian to submit additional tests to look for toxoplasmosis.
Immunoglobulin G (IgG) and Immunoglobulin M (IgM) antibody testing with the Immunoflourescence Assay (IFA) is the most common method of diagnosing toxoplasmosis. IgG-IFA antibodies do not develop until 2 weeks post infection and may remain high for several years. Therefore, high IgG-IFA antibody titers do not definitively diagnose an active infection. Instead, the diagnosis of active infection using IgG-IFA antibody titers requires that the titers increase fourfold over a 2-3 week period. Your veterinarian would need to draw two blood samples 3 weeks apart to demonstrate the rise in titers. An IgM-IFA antibody titer can be measured and can detect active infection. A positive IgM-IFA titer along with a negative IgG-IFA titer is diagnostic of an active infection. The reverse (positive IgG-IFA with negative IgM-IFA titers) would indicate a chronic infection.
An ELISA test may also be used to detect IgM antibodies. A high IgM-ELISA titer (>1:256) with a negative or low IgG-IFA titer indicates an active infection. Interpretation of titers is difficult and this information should be used in conjunction with other laboratory tests and the patient’s clinical condition to render a diagnosis.
Other tests that may aid in the diagnosis of toxoplasmosis include:
Thoracic (chest) radiographs are helpful to rule out other causes of respiratory compromise such as pneumonia, cancer, and fungal infection.
Analysis of cerebrospinal fluid obtained by a cerebrospinal fluid tap is used to help differentiate toxoplasmosis from other diseases causing central nervous system problems. The fluid is analyzed for red and white blood cells (none should be present) and antibody titers may be measured in the fluid as well. Test results must be assessed in conjunction with other findings in the patient as CSF analysis alone is not sufficient to provide a diagnosis.
On rare occasions, tachyzoites (one of the life cycle stages of toxoplasma) may be found in pleural (chest) or abdominal (belly) fluid that is obtained from a pet infected with toxoplasmosis. A sample for analysis is obtained by removing fluid from the pet’s chest or abdomen by sterile centesis. Because all pets with toxoplasmosis do not produce effusions, this test is limited to those that do produce effusions.
Additionally, tachyzoites may be found in fluid obtained by transtracheal aspirate in infected pets with pulmonary (lung) lesions. A transtracheal aspirate is performed with the pet under sedation. A sterile endotracheal tube is placed in the pet’s trachea (windpipe), sterile saline is squirted down the tube via a long sterile catheter, and the pet is induced to cough by gentle percussion of the chest wall. Fluid is then aspirated into a sterile syringe and examined under a microscope.
In-depth Information on Treatment
Because the results of some diagnostic tests (i.e. antibody tests) take several days to return, your veterinarian may need to initiate supportive therapy before a definitive diagnosis is made.
Antibiotics such as clindamycin, trimethoprim-sulfa, sulfonamides and pyrimethamine are administered to pets with toxoplasmosis. Clindamycin is the antibiotic of choice and is generally administered twice a day for 4 weeks. Trimethoprim-sulfa can be used alone or in combination with pyrimethamine. Both drugs are given twice daily for 4 weeks.
Anticonvulsant medications such as diazepam (Valium®), phenobarbital or pentobarbital may be used to control seizures.
Intravenous fluids and/or intravenous nutrition may be necessary for pets that are dehydrated or severely debilitated due to infection with toxoplasmosis. Nutritional support is particularly important while a patient is fighting an infection. If the pet is not vomiting but refuses to eat, your veterinarian may elect to place a naso-esophageal tube to permit feeding of a liquid diet. If the pet is vomiting, nutrition can be provided via a sterile intravenous catheter. Your pet may be referred to a 24- hour care practice or to a specialist for nutritional support.
Follow-up Care for Dogs with Toxoplasmosis
Administer any medications prescribed by your veterinarian. Some antibiotics may cause intestinal upset resulting in vomiting and diarrhea. If vomiting and diarrhea occur during the administration of an antibiotic, contact your veterinarian as soon as possible.
Encourage your pet to eat and drink. Pets that are unwilling to eat or drink should be re-examined immediately. Your veterinarian will schedule a recheck examination and will submit blood to recheck antibody titers after the course of antibiotic administration is completed.