Neosporosis: An Important Cause of Bovine Abortion
by Ephraim Keren, VDM, IC Newsletter Editor
Neospora caninum is a coccidian parasite that has been reported in various species of livestock. It is widely recognized as a major cause of abortion in cattle, but is rarely associated with other clinical signs. An epidemiological approach to dealing with N. caninum infections in cows requires identification of inapparently infected animals via serologic methods such as Biogal’s ImmunoComb® dot-ELISA kit.
Transmission
Vertical transmission from dam to fetus been described as the main route of transmission in endemically infected herds. N. caninum may also infect cows by ingestion of contaminated feedstuffs and/or direct contact with aborted fetal tissues. Horizontal transmission has been associated with storms of abortions in a herd. Seroconversion is seen in a high percentage of cattle in these outbreaks. Dogs infected with N. caninum are suspected to be a source of Neospora contamination of cow feed.
Clinical Disease
Abortion is the primary clinical sign associated with Neospora infection in mature cows. Cows with N. caninum antibodies (seropositive) are more likely to abort than seronegative cows. Most calves born from seropositive dams remain clinically normal, but remain chronically infected. Some calves may be born underweight or have neurological signs such as ataxia and decreased proprioception. Asymmetrical appearance of the eyes has also been reported.
Diagnosis
Serologic evidence in an aborting cow is indicative of exposure to N. caninum, but histological examination of the fetus is necessary for a definitive diagnosis of neosporosis. Fetal brain, heart, liver, placenta, and body fluids or blood serum are the best specimens for histology. Immunohistochemistry and PCR techniques may be used to confirm the histological diagnosis. These methods are relatively insensitive because the submitted tissues are usually autolyzed and contain few N. caninum organisms. Several serologic tests have be used to detect N. caninum antibodies including Biogal’s ImmunoComb® test and other ELISA’s, Immunoblot, the Indirect Fluorescent Antibody Test (IFA), and the Neospora Agglutination Test (NAT).
In pre-suckling calves, serum can be submitted for serologic diagnosis of congenital infection. Finding specific antibody in such a calf or in an aborted fetus indicates N. caninum infection. A negative result in a fetus does not necessarily rule out infection since antibody synthesis varies according to the stage of gestation, level of exposure, and the time between infection and abortion. Even a low IFA titer (e.g., 1:25) suggests N. caninum infection in fetuses. Blood, serum, and other body fluids (particularly peritoneal fluid) may be used for serologic diagnosis.
In serological assays, cut-off levels for determining significant antibody titers have not been standardized. In general, antibody levels are higher in cattle that have aborted due to neosporosis than those with normal pregnancy. However, titers in individual cows cannot determine etiology of abortions. Although N. caninum is closely related to Toxoplasma gondii, sarcocystis species and other Apicomplexans, cross reactivity with these other potential causes of abortion is not regarded as a problem in N. caninum sero-diagnostic tests.
Prevention and Control
Herd management, through selective breeding and culling, is thought to be the only way to prevent vertical transmission from cow to heifer. Following initial infection and abortion, a protective immunity appears to develop in these cows, which reduces or prevents subsequent abortions. This immunity appears to be more effective in animals that are reinfected from an external source (oocysts) than in congenitally infected cows that relapse.
References
1. Dubey J. P. (2003). Review of Neospora caninum and neosporosis in animals. The Korean Journal of Parasitology, 41(1), 1-16.
2. Atkinson, R. A., Cook, R.W., et al. (2000). Seroprevalence of Neospora caninum infection following an abortion outbreak in a dairy cattle herd. Aust Vet J., 78, 262-6.
3. Thurmond, M. C., Hietala, S. K. & Blanchard, P. C. (1997). Herd-based diagnosis of Neospora caninum–induced endemic and epidemic abortion in cows and evidence for congenital and postnatal transmission. J Vet Diag Invest, 9, 44-9.
Feline Panleucopenia – Part 2
by Ephraim Keren, VDM
This is the second part of an article on Feline Panleucopenia (FP). In Part 1 (which appeared in IC News #20) clinical signs, diagnosis, and conventional treatments were discussed. This article presents some homeopathic remedies and addresses the issues of vaccination and control.
Natural supportive treatments*
These treatments are aimed at enhancing the debilitated immune system in sick cats. They can be used in addition to the conventional supportive therapies. Homeopathic remedies are selected and matched according to the animal’s symptoms. They are given orally.
For cats that present with vomiting and diarrhea: Veratrum album is indicated for the weak, depressed and cold animal. Arsenicum album is indicated for anxious and restless animals that need warmth. (This remedy is also suitable when respiratory symptoms are present.)
For non-vomiting animals: Vitamin C in high doses; 100 mg a day in kittens to 250-500 mg twice a day to mature cats.
Aromatherapy (Inhalation) with essential oils: Rosemary, Tea tree, Geranium, Lavender.
Vaccination
Vaccination is the traditional and most successful approach for preventing Feline Panleucopenia. Both modified live and inactivated systemic vaccines are available. Both confer adequate immunity, though modified live vaccines may induce slightly greater and possibly more rapid protection. Inactivated vaccines however, are preferred for pregnant queens and young kittens.
There is a high degree of correlation between antibody titers in queens and maternally derived antibody (MDA) levels in kittens. High levels of MDA’s can interfere with immunization of kittens. To address this problem, veterinarians often give multiple vaccinations to kittens between 8 and 16 weeks of age. The last vaccination is administered when it is likely that the kitten can mount an active immune response after MDA levels have waned.
The duration of immunity in cats vaccinated with attenuated (modified live) vaccines is thought to be relatively long. Significant antibody titers have been shown to persist for at least 3 years following vaccination with these vaccines. Cats vaccinated with inactivated (killed) vaccines have slightly lower titers which are shorter lived (about a year).
A vaccination program should be tailored to the needs of the individual cat to ensure a good level of protection. For example, a new cat should be vaccinated within a year (and not less than 2 weeks) prior to being introduced to a multiple cat household or colony.
Breaks in immunity can lead to FP infection. They may be associated with:
» Lapses in vaccination programs.
» Ineffective vaccination (non-immunization because of interference by MDA’s)
» Compromised immunity (e.g. concurrent infection with FeLV, FIV).
» Individual immunological incompetence.
Prevention and Control
Measures in addition to vaccinations should be practiced to prevent transmission of FP infection. In boarding facilities, all cats should be housed individually, with their own equipment and utensils, and any animals with suspect clinical signs kept strictly isolated and fed last.
The occurrence of a clinical case will result in contamination of the environment. The following recommendations can help contain the infection and prevent new cases:
» Clean and disinfect all cages, bedding, and feeding utensils.
» Practice good hygiene by personnel, including cleaning of clothing and footwear.
» Assess immunity status in all cats by testing for specific anti- FP antibodies.
» Consider booster vaccinations in cats that do not have ’protective’ antibody levels.
» Wait to introduce new cats into the household. Only introduce cats that have ’protective’ antibody levels. (Test cats two weeks following vaccination.)
* We would like to express our thanks to Dr. Ronit Aboutbul for her contribution to this article.
References
(1) www.provet.co.uk/infectiousdiseases
(2) Feline Panleucopenia, The Merck Veterinary Manual, National Publishing Inc., 8th Ed.
From the Editor: Inapparent Infections Can Be Costly
Veterinarians, like other ’western oriented’ health-care providers, have been traditionally called upon first and foremost to treat the sick animals. However, owners of domestic animals are becoming increasingly aware that “an ounce of prevention is worth a pound of cure.” In other words, farmers and pet owners alike expect their veterinarians to be able to prevent infection and illness in their animals or at least recognize health problems at an early stage so that effective treatment can be implemented.
Serologic testing can help the veterinarian identify animals that may be infected with a particular agent but do not appear to be sick. As discussed in the lead article in this issue of the ImmunoComb® News, Neosporosis is such an infection. Abortion is only a clinical sign of this infection in most cattle. Although the cows appear clinically normal, up to 40% of the cows in a infected herd may abort. Dogs can also be infected by N. caninum and may transmit the organism to cattle by fecally contaminating animal feed.
The financial losses associated with bovine Neospora infections can be considerable. In addition to increased veterinary bills, there are the direct financial losses of the aborted calves and indirect losses from reduced milk production, poor weight gain, rebreeding, and replacement of culled cows. As such, it is important to identify the cause of abortions in the herd. Serologic testing is probably the most practical of doing this.
Leptospirosis is another infection that is associated with bovine abortions. Vaccinations have been widely used to help control Leptospirosis. However, vaccines are only available for some of the serovars associated with infections. So clinical cases continue to occur. The disease is well described and inapparent infections are also recognized in cows and dogs. These ’healthy’ carriers shed leptospirae in their urine, which contaminate the environment and pose an infectious hazard to other animals and people.
We have included the report of a possible clinical case of canine Leptospirosis in this issue of the IC News (Vet Forum) to illustrate how serology can be a valuable tool to help to diagnose individual clinical cases of Leptospirosis in animals with compatiable clinical signs. Diagnosing the cause of illness is the first step toward deciding on the proper treatment of the sick animal. We aould also like to point out that serology can help veterinarians provide better health care services for their clients by identifying animals that are inapparently infected with Leptospirosis.
Vet Forum
by Ephraim Keren, VDM
Question
An 18-month-old male Labrador retriever hunting dog recently presented to me. The owner reported that the dog had been acting lethargic for the past week or so and was not finishing his daily meal. Yesterday, he started drinking and urinating excessively.
Upon physical exam, the dog exhibited a low-grade fever and some tenderness upon abdominal palpation. Results of my initial laboratory work up (CBC, blood chemistry and urinalysis) were not remarkable. I am considering a diagnosis of Leptospirosis in this dog even though he was vaccinated for Lepto (with a multivalent vaccine) about a year ago. Will serology be helpful in this case?
Answer
Leptospira serology can certainly be helpful in evaluating the case you describe. The humoral immune response following vaccination with an inactivated Leptospira bacterin is typically low and relatively short lived (see table below). Therefore, I would expect to see high antibody levels in this dog if his illness is associated with Leptospirosis.
Your serology test result may be low positive or even negative if you test very early in the acute stage of illness. With a recent infection, you should see a rise in antibody levels if you perform a second test in 10- 14 days. One caveat: if the serologic test does not include the infecting serovar, a negative test result will not necessarily rule out Leptospira infection.
Canine Leptospirosis: Interpretation of Biogal’s ImmunoComb® Results
|
MAT(1) |
IC(2) Score |
Result |
Interpretation |
Recommendations in Clinical Cases |
| ≤ 1:50 |
0 – 1 |
Neg. |
Undetectable level of IgG antibodies to Leptospira serovar. |
Evaluate other diagnostic test data. Consider another etiologic agent. Retest in 10-14 days. |
| 1:100-200 |
2 – 3 |
Low Pos. |
Low titer of IgG antibodies to Leptospira serovar. |
Evaluate other diagnostic test data. Compare to previous IC result, if any(3). Consider another etiology and retest in 10-14 days. |
| 1:400-800 |
4 – 5 |
Med. Pos. |
Significant titer of IgG antibodies to Leptospira
serovar(4). |
Confirmatory evidence of natural exposure to Leptospira serovar. Medical treatment, as indicated. |
| ≥ 1:1600 |
6 |
High Pos. |
High titer of IgG antibodies to Leptospira serovar(4). |
Confirmatory evidence of natural exposure to Leptospira serovar. Medical treatment, as indicated. |
Footnotes:
(1) MAT = Microscopic Agglutination Test.
(2) IC = ImmunoComb® Antibody Test Kit.
(3) A low positive IC result may be associated with vaccination or recent natural exposure to Leptospirosis.
(4) Antibody titers associated with vaccination typically decline within several months. Post infection antibody levels may remain elevated up to 2 years. It is important to know when and with which serovars the dog was vaccinated.