ABSTRACT

Objective: This study aims to evaluate six clinical criteria for rabies diagnosis in live dogs. Design: Six clinical criteria that are collected from the history and clinical signs of dogs can diagnose rabies in live dogs. Materials and Methods: The data were collected in both retrospective and prospective studies at the Rabies Diagnostic Unit, Queen Saovabha Memorial Institute, Thai Red Cross Society. We analyzed reports of 1,170 dogs that were quarantined for 10 days in 1988-1996 and carried out a prospective study of 399 suspect dogs in 1997-2001. Results: We observed 90.4% sensitivity, 96.3% specificity and 94.8% accuracy of clinical diagnosis of rabies, using six criteria. Conclusion: These six clinical manifestations could be used for preliminary rabies diagnosis in live dogs.

INTRODUCTION

Rabies is a major public health problem in most of the world. Human deaths exceed 35,000-50,000 cases [1]. In Thailand, the disease is endemic with approximately 50 human deaths per year [2]. Dogs are the primary reservoir of rabies. Most human deaths are due to rabid dogs. In addition, most human postexposure treatments are due to dogs, both in Thailand and in the world [1]. Rabies prevention and control in many countries involves dog vaccination, population reduction, fertility control, case investigation, etc. Laboratory diagnosis is the basic tool for surveillance of rabies. The diagnosis in the brain of suspect animals obtains high accuracy and is accepted by the WHO, 1992 [3]. However, there is no acceptable method for diagnosis in live animals, with results that give high accuracy and practically. Currently, the observation and quarantine for 10 days of dogs and cats, and euthanasia of the suspect animals with examination by the fluorescent antibody test (FAT) is recommended [3]. The mouse inoculation test (MIT) is a confirmatory method to the FAT. At present, there are 2 basic steps for rabies diagnosis in live patients, clinical diagnosis and laboratory diagnosis. The clinical diagnosis of rabies is sometimes suggested by either epidemiological (history of exposure) or clinical (e.g., paresthesia, hydrophobia) findings [4]. However, no recent reports have been published for the accurate clinical diagnosis of rabies in dogs. Alternately, there are many reports for intravitam laboratory diagnosis of rabies in humans. Most conventional techniques used for the postmortem analysis of the brain are of limited value to support the intravitam diagnosis of rabies [5, 6, 7]. This observation is a problem for practicing veterinarians to manage suspect dogs that show nervous signs compatible with rabies. Thus, a practical method to diagnose rabies in the live dog would be a benefit. The aim of this study is to develop guidelines for preliminary diagnosis of rabies in live dogs, by using clinical examination and specific criteria to detect diagnose.

MATERIALS AND METHODS

Clinical signs and history were obtained from dogs suspected of rabies. A retrospective study was conducted by using 6 items in the clinical observations from 1,170 live dogs that had bitten humans. If the dog stayed alive more than 10 days it was not rabies. However, if the dogs died before 10 days of observation, we confirmed the diagnosis by FAT and MIT at the Rabies Diagnostic Unit, Queen Saovabha Memorial Institute, Thai Red Cross Society, between the years 1988-1996. We analyzed for sensitivity, specificity and accuracy of these methods. In addition, we use these 6 criteria for a prospective study in 399 live dogs observed between the years 1997-2001. Analysis for the data: the sensitivity, specificity and accuracy were calculated according to the method described by Mausner and Bahn [8].

Six basic items were used in the clinical rabies diagnosis in live dogs based on the following:

1.  How old is the dog?

a.  Less than 1 month Not rabies

b.  One month or more or not known (2)

2.  Is this dog sick or not?

a.  Normal (not sick) or sick more than 10 days Not rabies

b.  Sick less than 10 days or not known (3)

3.  How did the illness occur?

a.  Acute, spontaneous Not rabies (Normal one moment and suddenly ill the next)

b.  Gradual (not acute) or not known (4)

4.  How is the dog during last 3-5 days of the illness?

a.  Stable or improved (with no treatment) Not rabies

b.  Getting worse, or progressive or not known (5)

5.  Does this dog show signs of "Circling" in the cage and hit its head as if blind?

a.  Yes Not rabies

b.  No or not known (6)

6.  Does this dog show at least 2 clinical signs (below) during the last week?

a.  Yes Rabies

b.  No or showing only 1 clinical sign Not rabies

1.  Drooping jaw.

2.  Abnormal barking.

3.  Dry drooping tongue.

4.  Licking its own urine.

5.  Abnormal licking of water.

6.  Regurgitation.

7.  Altered behavior.

8.  Biting and eating the abnormal things.

9.  Aggression.

10. Biting with no provocation.

11. Running without apparent reason.

12. Stiffness upon running or walking.

13. Restlessness.

14. Bites during quarantine.

15. Appearing sleepy.

16. Imbalance of gait.

17. Frequent demonstration of the "Dog sitting" position.

RESULTS

First, the 6 criteria were analyzed for the retrospective study using the clinical sign reports in 1,170 live dogs that had bitten humans between the years 1988-1996. We found that these criteria produced 90.3% sensitivity, 96.0% specificity and 94.6% accuracy (Table I). In a second set, we analyzed the results of the 6 criteria for the prospective period between the years 1997-2001 in 399 live dogs that were observed and quarantined for 10 days after biting humans or animals. The sensitivity, specificity and accuracy in this series were 90.7%, 97.2% and 95.2% respectively (Table I). The combined results of these criteria in 1988-2001 were 90.4% sensitivity, 96.3% specificity and 94.8% accuracy (Table I).

DISCUSSION

Results of this investigation demonstrate approximately 10% false negatives and 3% false positives. Quite likely, these are due to the last clinical sign items. In addition, we do not screen out lateral recumbence in dogs that presented with coma or were unconscious, and hence could not show the obvious signs. Sending specimens for laboratory examination during the observation or 10 days quarantine for intravitam diagnosis could confirm the results. However, laboratory diagnosis for rabies in live animals is not practical, the results are uncertain (a negative result does not rule out of rabies) and some methods are quite expensive. Our method is a preliminary suggestion for clinical rabies diagnosis in dogs. This is not a decision-making process for the physicians to treat or not treat the patients bitten by these dogs. Limitations of our method include: it can not diagnose in rabies during the incubation period; dogs that are unconscious; dogs presenting with lateral recumbence related to traumatic injury of the head; dogs receiving the sedative drugs. The 6 clinical criteria could be used by veterinarians in their clinical evaluation of the dog with suspected encephalitis related to rabies.

ACKNOWLEDGEMENTS

This study was supported by Queen Saovabha Memorial Institute, Thai Red Cross Society. We thank Dr. Charles E. Rupprecht for helpful comments.

Table I. Comparison the retrospective, prospective and combined results of six clinical criteria with routine diagnosis in 1988-1996, 1997-2001 and 1988-2001. Routine diagnosis*

*If the dog stayed alive more than 10 days it was not rabies. If the dogs died before 10 days of observation, we confirmed brain by FAT and MIT.

REFERENCES

1.  World Health Organization: World survey of rabies No 34 for the year 1998. WHO/CDS/CSR/APH/99.6

2.  Rabies statistics. Annual Epidemiology Surveillance Report, Division of Epidemiology, Ministry of Public Health, Thailand, 1980-1998.

3.  WHO Expert Committee on Rabies. Eighth report. WHO Technical Report Series. Geneva: World Health Organization, 1992; 824:7-8.

4.  Hemachudha T. Human rabies: clinical aspects,pathogenesis and potential therapy. In: Rupprecht C E, Dietzschold B and Koprowski H (ed.), Lyssaviruses. Springer-Verlag, Berlin, Germany. 1994:121-144.

5.  Bourhy H, Sureau P. Laboratory methods for rabies diagnosis. Institut Pasteur, Paris, France. 1991.

6.  Hemachudha T, Phanuphak P, Sriwanthana B, Manutsathit S, Phanthumchinda K, Siriprasomsup W, Ukachoke C, Rasameechan S, Kaoroptham S. Immunologic study of human encephalitic and paralytic rabies. Am J Med, 1988; 84:673-677.

7.  Warrell MJ, Warrell DA. Rhabdovirus infections of humans. In: Porterfield JS (ed.), Exotic viral infections. Chapman & Hall Medical, London, United Kingdom. 1995:343-383.

8.  Mausner JS, Bahn AK. Epidemiology and Introductory Text. Philadelphia, London, Toronto: WB Sauders, 1974:245.