- How should the SNAP Feline Triple Test results be interpreted?
- What is the sensitivity and specificity of the SNAP Feline Triple Test?
- Can the test be used on kittens?
- How does the SNAP Feline Triple Test need to be stored?
- How many conjugate drops and sample drops do I need to run the SNAP Feline Triple Test?
- What is the read time for the SNAP Feline Triple Test?
- What type of samples can be used on the SNAP Feline Triple Test?
- What test quantities are available for sale?
- What is the dating on the SNAP Feline Triple Test?
- How are the SNAP Feline Triple Test kits shipped?
FIV/FeLV Questions:
- If I am vaccinating for FIV or FeLV, what is the diagnostic protocol?
- Will the FIV vaccine from Fort Dodge result in a positive SNAP FIV test result?
Feline Heartworm Disease Questions and Answers:
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What is feline heartworm disease?
Heartworm disease is a serious condition where worms reside in the heart and major blood vessels of dogs, cats and other species. The life cycle of heartworm begins when a mosquito bites an infected animal, such as a dog, with circulating microfilariae in its blood. As the mosquito feeds on the dog, it ingests the microfilariae. During the next 10 to 14 days, the microfilariae mature to the infective larval stage within the mosquito. When the mosquito bites its next meal source, such as a cat, it transmits the infective stage, also known as L3 larvae, to the cat.
Within three to four days the L3 larvae molt to L4 larvae and migrate in the subcutaneous tissues for approximately two months, at which time they molt to immature or juvenile worms (previously known as L5 larvae). The immature adults enter a peripheral vein and are transported via the blood to the distal pulmonary artery, where final maturation and mating occur. Many immature adults die after reaching the lungs, three to four months after infection. At this stage, the worms are about two inches long and the resultant inflammatory response causes significant lung pathology.
A small number of immature adults mature to adult heartworms in the lungs and heart of the cat. Under optimum conditions, completion of the life cycle takes 210 to 240 days. Most cats are amicrofilaremic and for this reason are dead-end hosts. However, microfilariae can be transiently found in about 20 percent of infected cats, seven to nine months after infection. Most heartworm infections in cats consist of one to six adult worms, making single sex infections not uncommon. Typically, heartworms live approximately two to four years in cats and may cause severe disease.
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My patient tested positive for feline heartworm antigen. What do I do now?
Testing Recommendations:
As indicated in the Feline Heartworm Antigen Diagnostic Algorithm, (developed with input from members of the American Heartworm Society, Companion Animal Parasite Council and IDEXX Laboratories), positive antigen tests are indicative of an adult heartworm infection.
This algorithm was developed with input from members of the American Heartworm Society. Companion Animal Council and IDEXX Laboratories. Refer to the American Heartworm Society guidelines (www.heartwormsociety.org) and the Companion Animal Parasite guidelines (www.capcvet.org) for complete feline heartworm disease testing, management and prevention recommendations.
Antigen testing is highly specific and results in few false positives. However, the American Heartworm Society and other industry leaders recommend following up positive tests with another antigen test and radiographs as well as blood work at the practitioner’s discretion. This will allow the practitioner to better understand the stage of infection in the cat.
In cats without clinical signs, case management may be limited to having the clients closely watch their cats for acute signs of illness. Educating pet owners to look for clinical signs of feline heartworm disease will help to prepare the clients in the event of clinical crises that would require cats to come directly to the practice. In addition, some practioners may consider sending patients home with emergency medication. According to the American Heartworm Society guidelines, retesting 6–12 months for seronegativity for feline heartworm and radiographic evidence of the disease’s progression and/or regression is appropriate. Refer to the American Heartworm Society guidelines at
www.heartwormsociety.org for complete testing, management and prevention recommendations.
For antigen-positive cats presenting with signs consistent with adult worm infection or Heartworm Associated Respiratory Disease (H.A.R.D.), further testing allows the practitioner to identify the stage of the disease. Radiographs, blood work and possibly echocardiography are indicated. Following treatment according to the American Heartworm Society guidelines, retesting 6–12 months for seronegativity for feline heartworm and radiographic evidence of the disease’s progression and/or regression is appropriate.
Also, cats testing positive for feline heartworm should be placed on prevention, because these cats are susceptible to additional infections and are obviously at risk for feline heartworm infection.
Therapy and Management:
Following are treatment recommendations from the American Heartworm Society (AHS):
Adulticide administration (melarsomine) is not recommended for use in cats. Cats therefore will eventually experience the death of the adult worm(s) at which time clinical manifestation is likely. Survival rates associated with feline heartworm infections are as high as 80 percent.1 Seroconversion of a positive antigen test to a negative status indicates the period of risk has probably passed, although it is possible for an undectable heartworm to remain.
Cats with radiographic changes consistent with heartworm or cats with clinical signs associated with adult or juvenile heartworm infections can benefit from supportive therapy.
| No outward clinical signs |
Monitor cat for a spontaneous cure, +/- prednisone (if supported by radiographic evidence of lung changes) |
| Typical signs—coughing, respiratory disease, vomiting |
Treat with a declining prednisone regimen of 2 mg/kg of body weight per day declining gradually to 0.5 mg/kg every other day |
| Acute signs |
Shock support therapy—parenteral fluids, oxygen therapy, cage confinement, bronchodilators, intravenous corticosteroids, cardiovascular drugs, antibiotics |
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Why did IDEXX put a feline heartworm antigen spot instead of an antibody spot on the SNAP Feline Triple Test?
If positive, the antigen spot on the SNAP Feline Triple Test provides a definitive diagnosis for adult heartworm infection. The disadvantage of an antigen test is that it cannot detect heartworm infection prior to the adult phase, which is about five to seven months postinfection. An antigen test will not detect cats with clinical signs associated with the juvenile stages of Heartworm Associated Respiratory Disease (H.A.R.D.).
Antibody tests detect exposure as early as two months post-exposure. However, an antibody test cannot differentiate between cats that are infected and cats that have cleared their infection. To further complicate this picture, cats on prevention can become antibody positive because an antibody response can be mounted before the preventative successfully clears the larvae stage.
Antigen tests offer a definitive answer and the least confusion because they are diagnostic for adult heartworm infection, which is why IDEXX chose the antigen option. (Please note that the American Heartworm Society recommends running an antigen and an antibody test together.)
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What is the "Tip of the Iceberg" as it relates to feline heartworm and how does it help me estimate disease prevalence in my practice?
With the addition of a heartworm antigen spot to the SNAP® FIV/FeLV Combo Test, the SNAP Feline Triple Test will result in millions of cats being tested for feline heartworm. It is important, however, to understand the limitations of heartworm testing in the cat. Antigen testing illuminates only adult worm infections, which is only a small part of the total feline heartworm disease picture.
To help veterinarians understand how testing for feline heartworm can improve their ability to 1) manage individual cases, and 2) understand the risk of feline heartworm disease in their region, key opinion leaders have developed a concept they are calling the “Tip of the Iceberg.” Using published studies, it is possible to construct a predictive model that relates the number of antigen positives found in a practice area to the overall impact of the disease.
Testing with the SNAP Feline Triple Test will “find” tens of thousands of heartworm positives per year, but this is just the “Tip of the Iceberg.” It has been proposed that for every antigen positive, there are 10 times as many cats infected with Heartworm Associated Respiratory Disease (H.A.R.D.) and even more are at risk of exposure to feline heartworm. To review, H.A.R.D. is the inflammatory response associated with juvenile or adult worm death. Only reproductively active adults express enough antigen in quantities that are detectable on the SNAP Feline Triple Test.
Current thinking suggests that for every antigen positive, approximately 10 other cats are infected or are at risk for H.A.R.D. Use the “Tip of the Iceberg” model to help determine if prevention of heartworm and H.A.R.D. is appropriate in your practice.
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What are the clinical signs of feline heartworm disease?
The clinical signs of heartworm infection in cats can be nonspecific and can take the form of respiratory, gastrointestinal or occasionally, neurological manifestations. These respiratory signs may be transient and resolve in a couple of days. Feline heartworm infection may mimic other feline diseases, which makes diagnosis by clinical signs alone difficult. These clinical signs, such as intermittent coughing, asthma-like signs, chronic respiratory disease/respiratory distress or vomiting have all been associated with heartworm infection.
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Which cats should be tested with the SNAP Feline Triple Test?
Cats infected with FIV, FeLV and feline heartworm present with multiple signs. However, it is common for infected cats to present with no clinical signs at all. Some of the most common reasons for testing cats are listed below.
Which cats to test?
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What are the American Heartworm Society guidelines on feline heartworm testing?
The American Heartworm Society (AHS) feline heartworm guidelines support screening healthy cats with a feline heartworm antigen test. However, the preferred method is to screen healthy cats with both antibody and antigen tests.
For cats presenting with clinical signs consistent with Heartworm Associated Respiratory Disease (H.A.R.D.), AHS recommends complementing antigen and antibody tests with thoracic radiography and/or echocardiography.
The American Heartworm Society recommends testing to monitor the clinical course of cats that have already been diagnosed with feline heartworm infection and to establish a baseline reference point prior to initiation of prevention.
Refer to the American Heartworm Society guidelines at www.heartwormsociety.org for complete testing, management and prevention recommendations.
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After a mosquito bite, when can I expect to see a positive feline heartworm result on the SNAP Feline Triple Test?
The SNAP Feline Triple Test can detect adult heartworm at approximately five to seven months post infection.
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Are cats designated as "indoor-only" at risk for feline heartworm?
Yes. Several studies have investigated the risk of feline heartworm to indoor cats. In those studies, it has been found that up to one-fourth of cats diagnosed with feline heartworm were classified as indoor-only.1,2
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I have a cat that is positive for adult heartworm antigen. How long before I need to run a follow-up test?
Following treatment according to the American Heartworm Society guidelines, retesting 6–12 months for seronegativity for feline heartworm and radiographic evidence of the disease’s progression and/or regression is appropriate. Refer to the American Heartworm Society guidelines at www.heartwormsociety.org for complete testing, management and prevention recommendations.
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There’s no treatment, so why test?
Testing your patients can help identify the prevalence of heartworm disease in your practice population and help you determine whether feline heartworm preventatives are appropriate in your practice.
While there is not a cure for heartworm infection, the reported survival rates are as high as 80%1; and cats with clinical signs of the disease can be managed. The American Heartworm Society guidelines list specific therapies available for heartworm-infected cats with or without acute signs. Therapies range from treating obvious clinical signs with prednisone to stabilizing acutely ill cats with treatments appropriate for shock.
In addition to testing cats suspected of heartworm infection, the American Heartworm Society recommends testing to monitor the clinical course of those cats that have already been diagnosed with feline heartworm infection and to establish a baseline reference point prior to the initiation of prevention.
SNAP Feline Triple Test Questions and Answers:
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What is the SNAP Feline Triple Test?
The SNAP Feline Triple Test is an updated version of IDEXX’s industry standard SNAP FIV/FeLV Combo Test. The SNAP Feline Triple Test screens cats for feline immunodeficiency virus (FIV) antibody, feline leukemia virus (FeLV) antigen and feline heartworm (FHW) antigen. This three-in-one test for feline infectious diseases introduces an enhanced tool to promote feline health care.
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What is the positioning of the test spots on the SNAP Feline Triple Test?
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How should the SNAP Feline Triple Test results be interpreted?
A heartworm antigen positive result is indicative of an adult heartworm infection. However, a negative test does not rule out feline heartworm infection. The recent discoveries associated with Heartworm Associated Respiratory Disease (H.A.R.D.) highlight an unfortunate drawback of antigen testing; antigen tests miss the early stage of feline heartworm disease associated with the immature adults. In cases where adult heartworm or H.A.R.D. are suspected, a negative antigen test should be followed up with an antibody test and may warrant additional tests such as radiographs and echocardiography as well as blood work.
An FIV antibody positive result indicates that a cat has been infected with FIV and may have an active infection.
An FeLV antigen positive result indicates that the cat is infected with FeLV.
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What is the sensitivity and specificity of the SNAP Feline Triple Test?
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Can the test be used on kittens?
The SNAP Feline Triple Test can be used on kittens to screen for FIV and FeLV. The feline heartworm spot is not valid for young kittens because it requires five to seven months post infection for antigen loads to be detectable on an antigen test. The heartworm spot on the test should be used on cats older than seven months of age.
If a cat under six months of age is negative for FIV, infection is unlikely. Kittens born to infected queens may test positive for antibody. Kittens tested before six months of age that are positive should be retested at 60-day intervals. If tests performed after six months of age are still confirmed positive, these kittens should be considered infected.3
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How does the SNAP Feline Triple Test need to be stored?
As with the SNAP FIV/FeLV Combo Test, the SNAP Feline Triple Test will need to be refrigerated.
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How many conjugate drops and sample drops do I need to run the SNAP Feline Triple Test?
The SNAP Feline Triple Test requires four drops of conjugate and three drops of sample.
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What is the read time for the SNAP Feline Triple Test?
The read time is 10 minutes, the same as the SNAP FIV/FeLV Combo Test.
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What type of samples can be used on the SNAP Feline Triple Test?
As with the SNAP FIV/FeLV Combo Test, serum, plasma or anticoagulated whole blood can be utilized to perform the SNAP Feline Triple Test.
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What test quantities are available for sale?
The SNAP Feline Triple Test will be available for sale in 15- and 30-test-kit quantities.
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What is the dating on the SNAP Feline Triple Test?
The shelf life of the SNAP Feline Triple Test will be eight months at launch. We expect to extend this as we generate real-time stability results.
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How are the SNAP Feline Triple Test kits shipped?
Kits will be shipped to customers ambient (without ice) via a two-day FedEx shipment.
FIV/FeLV Questions and Answers:
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If I am vaccinating for FIV or FeLV, what is the diagnostic protocol?
If the client chooses to vaccinate, the American Association of Feline Practioners (AAFP) guidelines suggest that the cat be tested prior to vaccination.4,5
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Will the FIV vaccine from Fort Dodge result in a positive SNAP FIV test result?
Yes, the FIV vaccination cross-reacts with the SNAP Feline Triple Test because the test detects FIV antibodies. There is no commercially available, licensed test that can differentiate between the vaccine and natural infection.
| References: |
| 1. |
Genchi C, et al. Statistical Elaboration of Life Expectancy, Cause of Death and Duration of Infection in Cats Infected with Dirofilaria immitis. Proceedings from: AHS 2007 Heartworm Symposium; July 13 to 14,2007. Washington, D.C. |
| 2. |
Atkins CE, DeFrancesco TC, Coats JB, et al. Heartworm Infections in Cats: 50 Cases (1985–1997). J Am Vet Med Assoc. 2000;217(3):355–8. |
| 3. |
AAFP. Report of the American Assoication of Feline Practitioners and Academy of Feline Medicine Advisory Panel on Feline Retrovirus Testing and Management. 2005. |
| 4. |
AAFP. American Association of Feline
Practitioners information brief: In response to inquiries regarding Fel-O-Vax® FIV.
Available at: www.AAFPonline.org/resources/statements/felovax.htm. |
| 5. |
AAFP. American Association of Feline
Practitioners and Academy of Feline Medicine Advisory Panel on Feline Vaccines.
Available at: www.AAFPonline.org/resources/guidelines/2006_Vaccination_Guidelines_JAVMA.pdf.  (648 KB) |
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