-from Epidemiological Bulletin, Vol. 21 No. 3, September 2000-

Case Definitions:
Anthrax, Brucellosis and Rabies


Anthrax

Rationale for surveillance
Anthrax is a widespread zoonosis transmitted from domestic animals (cattle, sheep, goats, buffaloes, pigs and other) to humans by direct contact or through animal products. Human anthrax is a serious problem in several countries and has potential for explosive outbreaks (especially the gastro-intestinal form); while pulmonary (inhalation) anthrax is mainly occupational, the threat of biological warfare attacks should not be forgotten. Anthrax has a serious impact on the trade of animal products.
The control of anthrax is based on its prevention in livestock: programmes based only on prevention in humans are costly and likely to be ineffective except for those industrially exposed. There is an effective vaccine for those occupationally exposed, and successful vaccines for livestock, particularly for herds with ongoing exposure to contaminated soil. In most countries anthrax is a notifiable disease. Surveillance is important to monitor the control programmes and to detect outbreaks.

Recommended case definition
Clinical description
An illness with acute onset characterized by several clinical forms. These are:
(a) localised form: (more frequent)
cutaneous: skin lesion evolving over 2 to 6 days from a papular through a vesicular stage, to a depressed black eschar invariably accompanied by oedema that may be mild to extensive.
(b) systemic forms: (sporadic)
gastro-intestinal: abdominal distress characterized by nausea, vomiting, anorexia and followed by fever.
pulmonary (inhalation): brief prodrome resembling acute viral respiratory illness, followed by rapid onset of hypoxia, dyspnoea and high temperature, with X-ray evidence of mediastinal widening.
meningeal: acute onset of high fever possibly with convulsions, loss of consciousness, meningeal signs and symptoms; commonly noted in all systemic infections.

Laboratory criteria for diagnosis
Laboratory confirmation by one or more of the following:
Isolation of Bacillus anthracis from a clinical specimen (e.g., blood, lesions, discharges).
Demonstration of B. anthracis in a clinical specimen by microscopic examination of stained smears (vesicular fluid, blood, cerebrospinal fluid, pleural fluid, stools).
Positive serology (ELISA, Western blot, toxin detection, chromatographic assay, fluorescent antibody test (FAT)).

Note: It may be not possible to demonstrate B. anthracis in clinical specimens if the patient has been treated with antimicrobial agents.

Case classification
Suspected: A case that is compatible with the clinical description and has an epidemiological link to confirmed or suspected animal cases or contaminated animal products.
Probable: A suspected case that has a positive reaction to allergic skin test (in non-vaccinated individuals).
Confirmed: A suspected case that is laboratory-confirmed.

Recommended types of surveillance
Since the usual ratio of livestock cases to human cases is of the order of 10-20:1, it is ineffective to depend only on human case reports. Routine surveillance must be undertaken, especially in high-risk groups (slaughterhouse workers, shepherds, veterinarians, wool/hide workers), and unexplained sudden livestock deaths must be investigated. Mandatory immediate case-based reporting from peripheral level (health care providers or laboratory) to intermediate and central levels of public health sector and to the appropriate level of animal health sector. All cases must be investigated.
Routine monthly reporting of aggregated data on confirmed cases and investigation reports from intermediate to central level in public health and animal health sectors.

Recommended minimum data elements
Case-based data for investigation and reporting:
Case classification by type (suspected / probable / confirmed), and by clinical form (cutaneous / gastro-intestinal / pulmonary (inhalation) / meningeal)
Unique identifier, age, sex, geographical information, occupation
Date of onset, date of reporting
Exposure history
Outcome.

Aggregated data for reporting to central level:
Number of confirmed cases by age, sex, clinical form (cutaneous / gastro-intestinal / pulmonary (inhalation) / meningeal).
Similarly for livestock by outbreaks and cases in relation to species and appropriate geographic / administrative area.

Principal uses of data for decision-making
Surveillance data
Estimate the magnitude of the problem in humans and animals
Monitor the distribution and spread of the disease in humans and animals
Detect outbreaks in humans and animals
Monitor and evaluate the impact of prevention activities in humans and of control measures in animals

Investigation data
Identify populations at risk
Identify potentially contaminated products of animal origin
Identify potentially contaminated animal sources (herds or flocks)

Back to top

 


Brucellosis

Rationale for surveillance
Brucellosis is a widespread zoonosis transmitted from animals (cattle, sheep, goats, pigs, camels and buffaloes), through direct contact with blood, placenta, foetuses or uterine secretions, or through consumption of infected raw animal products (especially milk and milk products). Human brucellosis due to Brucella melitensis has serious public health consequences in areas where goat and sheep are raised. Brucellosis has an important world-wide impact on human health and the animal industry. In most countries brucellosis is a notifiable disease. Control measures are based on prevention of risk factors. Surveillance is a key element for management of prevention and control programmes.

Recommended case definitions
Clinical description:
An illness characterized by acute or insidious onset, with continued, intermittent or irregular fever of variable duration, profuse sweating particularly at night, fatigue, anorexia, weight loss, headache, arthralgia and generalized aching. Local infection of various organs may occur.

Laboratory criteria for diagnosis
Isolation of Brucella spp. from clinical specimen or
Brucella agglutination titre (e.g., standard tube agglutination tests: SAT>160) in one or more serum specimens obtained after onset of symptoms or
ELISA (IgA, IgG, IgM), 2-mercaptoethanol test, complement fixation test, Coombs, fluorescent antibody test (FAT), and radioimmunoassay for detecting antilipopolysaccharide antibodies; and counterimmunoelectrophoresis (CIEP)

Case classification
Suspected
:A case that is compatible with the clinical description and is epidemiologically linked to suspected or confirmed animal cases or contaminated animal products.
Probable: A suspected case that has a positive Rose Bengal test.
Confirmed: A suspected or probable case that is laboratory-confirmed.

Recommended types of surveillance
Routine surveillance must be undertaken, particularly among high-risk groups (farmers, shepherds, workers in slaughterhouses, butchers, veterinarians, laboratory personnel).
Mandatory early case-based reporting by health care providers or laboratory to upper levels of the public health sector as well as to the appropriate level of the animal health sector. In endemic countries where investigation of all reported cases may not be feasible, a representative proportion of reported cases should be investigated routinely.

Recommended minimum data elements
Case-based data for investigation and reporting
Case classification
Unique identifier, age, sex, geographical information and occupation
Date of clinical onset, date of reporting
Exposure history
Outcome.

Aggregated data
Number of cases by case classification (probable / confirmed), age, sex, geographical area, occupation.

Principal use of data for decision-making
Surveillance data
Estimate the magnitude of the problem in humans and animals
Monitor the distribution of the disease in humans and animals
Monitor and evaluate impact of prevention activities in humans, and of control / elimination measures in animals.

Investigation data
Identify populations at risk
Identify potentially contaminated products of animal origin.
Identify potentially infected animal sources (herds or flocks)

Back to top


Rabies

Rationale for surveillance
Rabies, present on all continents and endemic in most African and Asian countries, is a fatal zoonotic viral disease, transmitted to humans through contact (mainly bites and scratches) with infected animals both domestic and wild. Over 40 000 human deaths are estimated to occur each year world-wide, most of them in the developing world (mainly in Asia), and an estimated 10 million people receive post-exposure treatment after being exposed to animals suspected of rabies.

WHO promotes:
human rabies prevention through well-targeted post exposure treatment and increased availability of modern rabies vaccine.
disease elimination through mass vaccination of dogs and other animal reservoirs. Surveillance of both human and animal rabies is essential to detect high risk areas and outbreaks quickly and to monitor the use of vaccine.

Recommended case definition
Clinical description
An acute neurological syndrome (encephalitis) dominated by forms of hyperactivity followed by paralytic syndromes that progresses towards coma and death, usually by respiratory failure, within 4 to 7 days after the first symptom if no intensive care is instituted. Bites or scratches from a suspected animal can usually be traced back in the patient medical history. The incubation period may vary from days to years but usually falls between 30 and 90 days.

Laboratory criteria for diagnosis
One or more of the following
Detection of rabies antigen by direct fluorescent antibody (FA) in clinical specimens, preferably brain tissue (collected post mortem).
Detection of rabies antigen by FA on skin or corneal smear (collected ante mortem).
FA positive after inoculation of brain tissue, saliva or CSF in cell culture, in mice or in suckling mice.
Detectable rabies-neutralising antibody titre in the CSF of an unvaccinated person.
Identification of viral antigens by PCR on fixed tissue collected post mortem or in a clinical specimen (brain tissue or skin, cornea or saliva).
Isolation of rabies virus from clinical specimens and confirmation of rabies viral antigens by direct fluorescent antibody testing.

Case classification
HUMAN RABIES:
Suspected: A case that is compatible with the clinical description.
Probable: A suspected case plus history of contact with suspected rabid animal.
Confirmed: A suspected case that is laboratory-confirmed.

HUMAN EXPOSURE TO RABIES:
Possibly exposed: A person who had close contact (usually a bite or scratch) with a rabies-susceptible animal in (or originating from) a rabies-infected area. Exposed: A person who had a close contact (usually a bite or scratch) with a laboratory-confirmed rabid animal.

Recommended types of surveillance
SURVEILLANCE IN HUMAN POPULATIONS:
Surveillance of human exposure to rabies:
At peripheral level, especially in rabies-infected areas, reports of patients with a history of animal contact (usually a bite / scratch) should be investigated at once; when required, they should be treated as an emergency. Case-based and aggregated data must be sent regularly from peripheral to intermediate and central level.

Surveillance of cases of human rabies:
Immediate reporting of suspected and confirmed cases from peripheral level (by diagnosing physician and laboratory) to intermediate and central level. Rapid exchange of information with services in charge of animal rabies surveillance and control is required.

Epidemiological investigation of outbreaks: Investigation of all rabies foci, identifying sources of infection as well as humans and animals exposed or possibly exposed.

SURVEILLANCE IN ANIMAL POPULATIONS (EPIZOOTIC CONTROL):
Where the disease is endemic or could be reintroduced, surveillance of animal rabies and similar conditions in wild and domestic species most likely to be reservoirs of disease must be undertaken. Surveillance is laboratory-based. Immediate submission of brain specimen of suspected animal for laboratory diagnosis when human exposure occurs. Suspected domestic animals at the origin of human exposure that cannot be killed must be kept under observation for 10 days. Rapid exchange of information between services in charge of human and animal rabies surveillance and control is required.

Recommended minimum data elements
HUMAN RABIES EXPOSURE
Case-based data: Unique identifier, name, age, geographical information, date(s) of bite / scratch, geographical information (location) of biting episode(s), category of exposure, local wound treatment, previous rabies vaccination and rabies immunoglobulin (human or animal origin) taken, current treatment, outcome; information on biting animal, vaccination history, outcome.

Aggregated data: Exposures by geographical information on biting episode, biting animal, outcome in animal and human populations.

SURVEILLANCE OF DEATHS FROM HUMAN RABIES:
Unique identifier, name, age, geographical information, date of onset of symptoms, date(s) of bite/scratch, geographical information (location) of biting episode(s), site of bite on the body, nature of bite, local wound treatment, vaccination history, previous serum treatment, hospital, treatment details, outcome, details of biting animal, samples taken, sample results.

Principal uses of data for decision-making:
Detect outbreaks in endemic areas and new cases in rabies-free area.
Determine high-risk areas for intervention.
Rationalise the use of vaccine and immunoglobulin.
Evaluate effectiveness of intervention at the level of the animal reservoir and exposed human population.

To view the last article on rabies from the Epidemiological Bulletin: Vol. 16, No. 1, March 1995 issue.

 

Return to the Index,
Epidemiological Bulletin , Vol. 21 No. 3, September 2000