Epidemiology of bacterial zoonotic diseases with their prevention and control

EPIDEMIOLOGYOF

ZOONOTIC BACTERIAL DISEASES

WITHTHEIR PREVENTION AND

CONTROL

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BRUCELLOSIS• It is one of the major bacterial zoonotic disease and in

humans is also known as undulent fever ,malta fever or mediterranean fever.

• it is caused by different species of brucella group of organisms

• It is characterized by: enlarged spleen arthritis irregular febrile attacks with profuse sweating• The disease may last for several days,months or years

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• Brucellosis is a recognised public health problem with worldwide distribution.

• It is endemic wherever cattle,pigs,goats and sheep are raised in large numbers.

• Important endemic area for brucellosis exist in Mediterranean zones,europe,central asia,mexico and

south America.• Animal brucellosis is reported from practically every

state in india.• And human brucellosis is difficult to estimate

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EPIDEMIOLOGICAL DETERMINANTS AGENT FACTORS1. AGENT: the agents are small,gram negative

rod shaped,non-motile,non-sporing and intracellular coccobacilli of the genous Brucella.

Four species infect man: (a) B.melitensis : most virulent and invasive species; usually infects goats and sheeps.

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(b) B.abortus: less virulent and is primarly (c) B.suis: intermediate virulent and chiefly (d) B.canis:is a parasite of dogs.

2. RESERVOIR OF INFECTIONThe reservoir for human infection are:-

cattle,goats,swine,buffaloes,horses and dogs.

disease of cattle.

infects pigs.

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• The infected animal excrete Brucella in urine,milk,placenta,uterine and vaginal discharges.

HOST FACTORS:-• Human brucellosis is predominantly a disease

of adult male.• People at high risk are-

farmers,butchers,shephards ,abattoir workers and lab workers , due to occupational exposure

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• ENVOIRMENTAL FACTORSConditions favouring the spread of brucellosis are:Absence of standards of hygieneOvercrowding of herdsLack of exposure to sunlightUnhygienic practices in milk and meat

productionINCUBATION PERIODHighly variable,usually 1-3 weeks,but may last for

6 months or more.

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TransmissionROUTES OF TRANSMISSION• Oral : unpasteurised milk & products, raw milk or

meat• Respiratory: lab workers.• Skin: accidental penetration or abrasion– - at risk farmers & veterinarians.

• Other routes:Conjunctival, Blood transfusion, Transplacental, person to person.

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PATTERN OF DISEASE• It may vary from an acute febrile disease to a chronic low grade disease.• The acute phase is characterized by: pyrexia(up to 40-41deg c) rigors and sweating arthritis/arthralgia involving larger joints. low back pain headache insomnia spleenomegaly and hepatomegaly leucopenia If patient is treated with tetracycline,the symptoms may disappear

quickly ,but infection ,being intracellular,may persist giving rise to subacute or relapsing disease.

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CONTROL OF BRUCELLOSIS• IN THE ANIMALSThe most rational approach for preventing human brucellosis is control and eradication of

the infection from animal reservoirs which is based on combination of the following measures:

(a)TEST AND SLAUGHTER: case finding done by mass survey. Skin test are available. The complement fixation test is recommended.

Those animals infected with brucellosis are slaughtered with full compensation paid to farmers.

This is the only satisfactory solution aimed at eradication of the disease.(b)VACCINATION: vaccine of B.abortus strain 19 is commonly used for young animals. a

compulsory vaccination programme is given on yearly basis to reduce rate of infection.Systemic vaccination of period of 7-10 years may result in elimination of the disease(c) HYGIENIC MEASURES: these comprise provision of clean sanitary envoirnment for

animals sanitary disposal of urine and faeces and health eduction of all those who are occupationaly involved

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• IN THE HUMANS(a) EARLY DIAGNOSIS AND TREATMENT: in uncomplicated case the antibiotic of choice is tetracycline .For adults in the acute stage ,the dose is 500g every 6 hours for 3

weeks.In patients with skeletal or other complication , intramuscular

streptomycin 1g daily in addition to tetracycline usually achieves a cure.

(b) PASTEURIZATION OF MILK (c) PROTECTIVE MEASURES-prevent direct contact with infected

animals. persons at risk should observe high standards of personal

hygiene. They should wear protective clothing when handling carcasses. Exposed areas of skin should be washed and soiled clothing

renewed

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(d)VACCINATION : human live vaccine of B.abortus strain 19-BA is available.

BRUCELLOSIS WOULD DISAPPEAR IF IT WERE ERADICATED FROM ANIMALS.

The national and international centre for brucellosis is located at FAO/WHO Brucella reference centre, Indian veterinary research institute ,Izatnagar,(Uttar Pradesh).

HUMAN SALMONELLOSIS

• The term ‘salmonellosis’ covers a complex group of food borne infections affecting both man and animals. The disease causes illness and even death in humans as well as economic losses in the animal and food industries. The term ‘food poisoning’ is commonly applied to salmonellosis.

PROBLEM STATEMENT

• Salmonellosis is a global problem. Human salmonellosis represents 60 to 80% of all reported cases of food borne diseases.

• While the incidence of typhoid fever has declined, the incidence of other salmonella infections has increased in the developed countries. The problem is aggrevated by the widespread use of animal feeds containing antimicrobial drugs that favour drug-resistant salmonellae and their potential transmission to humans.

EPIDEMIOLOGICAL DETERMINANTS

AGENT FACTORSAGENT:- Salmonellae comprises a large and important

group of bacteria. This group is now known to comprise more than 2,500 serotypes capable of infecting humans.

Compared with other gram-negative rods, salmonellae are relatively resistant to various environmental factors. They have been shown to be resistant to drying, salting, smoking and freezing even for years.

Cont..

• As a result, salmonellae have been isolated from divergent foods such as chocolates, biscuits, coconuts and spices. The bacterium is sensitive to heat and will survive temperatures above 70 degree centigrade.

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Cont..

• From an epidemiological point of view, salmonellae can be classified into three main groups:-

(i) Those which infect only man- e.g S. typhi, S. paratyphi A and C.

(ii) Those are host- S. cholera-suis , S. Dublin.(iii) Those infect both man and animals- S.

typhimurium, S. Enteriditis.

Cont..RESERVOIR AND SOURCE OF INFECTION:-(a) FOODS Foods of animal origin, particularly commercially prepared foods

such as meat, poultry and egg products are considered to be primary sources of salmonellosis.

(b) ANIMALS Animals are the hosts and the principal vectors of zoonotic

salmonellosis. E.g cattle, swine, rodents etc.(c) ENVIRONMENT Salmonellae are widely distributed in the environment in dust,

water, manure, sewage, sludge, vegetables, insects, birds, fish, rodents and other mammals.

MODE OF TRANSMISSION

• By ingestion of contaminated food and drink, direct contact with domestic animals especially such as dogs, pigeons, rats, mice and insects. Once man is infected, he becomes a source and the infection may spread to others by the faecal-oral route.

• INCUBATION PERIOD:- 6 to 72 hours (usually).

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CLINICAL FEATURES• Clinically, the disease may be manifest by one of the three

syndromes:(i) ENTERIC FEVER:- the term ‘enteric fever’ includes both

typhoid and paratyphoid fevers. The disease may occur sporadically, epidemically or endemically.

(ii) SALMONELLA ENTEROCOLITIS (gastroenteritis) : This is the most common manifestation of Salmonellae infection. 6 to 48 hours of ingestion of Salmonellae there is nausea, headache, vomiting and diarrhoea. Low grade fever is common. Most infections are mild with diarrhoea, in severe cases there may be dehydration.

Cont..

(iii) SEPTICAEMIA WITH FOCAL LESION:- Non-typhoid salmonellae may occasionally invade the blood stream leading to generalized or localized infection presenting itself as pyrexia of unknown origin. Focal infection may result in osteomyelitis, pyelonephritis, arthritis, meningitis, cholecystitis and endocarditis.

PREVENTON AND CONTROL

• Since salmonellosis is zoonotic in origin, preventive measures should begin at the farm and embrace all the elements of the food chain through live animals, animal products, processing, final food preparation to consumption. Approaches indicated at the farm level are :

(i) Disease control e.g immunization of farm animals against salmonellosis.

(ii) The use of hygienic animal feed.(iii) Ensuring a sanitary environment for the animals

LEPTOSPIROSISLeptospirosis is essentially animal infection by several serotype of liptospira & transmitted to man under certain environmental condition.The disease manifestations are many & varied, ranging severity from a mild febrile illness to severe & sometime fatal disease with liver & kidney involvement.

• Leptospirosis is considered to be most widespread of the disease transmissible from animals to man

• It has high prevalence in warm humid tropical countries. Out break mostly occur as a result of heavy rain fall.

• The global burden of disease in unknown approx 500,000 cases of leptospirosis are estimated to occur worldwide every year

EPIDEMOLOGICAL DETERMINATIONAgent factor (a) Agent: leptospira are thin & light motile spirochetes 0.1-0.2 µm wide & 5-15µm long & hooked ends. This organisms are visible by dark- field illumination & silver staining. (b) Source of infection: leptospira are excreted in the urine of infections animal for a long time often for an enter life time in case of rodents.

(c)Animal reservoirs: leptospirosis effects wild & domestic animal worldwide especially rodents such as rat ,mice etc. most domestic animal including cattle ship , goat, water buffallo, pigs & horse may be infected through pet animal particularly dogs may also be infected.

Host factors (a)Age: children acquire the infection from dogs more frequently then do adults. Human infection is only accidental. (b)occupation: human infections are usually due to occupational exposure to the urine of infected animals e.g.- Agriculture,livestocks farmers, workers in rice fields ,sugarcane fields etc.(c)Immunity: A solid serovar specific immunity follows infection.

Environmental factors• Leptospirosis infection is unique in that it is acquired

through contact with an environment contaminated by urine and faeces from carrier animal or other infected animals.

• Leptospira shed in the urine can survive for wks in soil and water, so environmental contamination may reach high levels in areas where carrier animals frequently urinate.

• The association of poor housing, limited water supply, inadequate method of water disposal, all combine to make the disease a significant risk for the poor population in both urban and rural areas.

Mode of transmission (a) Direct contact: leptospira can enter the

body through skin abrasions or through intact mucous membrane by direct contact with urine or tissue of infected animal.

(b) Indirect contact :through the contact of the broken skin with soil, water or vegetation contamination by urine of infected animals or through ingestion of food or water contaminated with leptospirosis.

(c) Droplet infection: infection may also occur through inhalation as when milking infected cows or goats by breathing air polluted with droplets of urine.

Direct man to man infection is rare.

• Incubation period:

Usually 10 days with a range of 4 to 20 days

Diagnosis• It is not possible to diagnose leptospirosis with

certainty on clinical grounds alone. Because of the wide spectrum of sign & symptoms, thee diagnosis is made by isolation of leptospires from blood during the acute illness and from urine after the 1 wks.

• Early in the disease the organisms may be identified by dark fields examination of the patient’s blood or by culture on a semisolid medium.

• The organism may also be grown from the urine from 10th day to 6 wks.

• Diagnosis is usually made by means of serological tests , of which several are available.

• Agglutination tests & become positive after 7-8 days of illness and peaks at 3-4 wks & may persist at high level for many yrs.

• indirect haemagglutination , immunoflourescent antibody and ELISA tests also available .

Control(a) antibiotics: penicillin is the drugs of choice by

other antibiotics(tetracycline & doxycycline) are also effective

(b) Environmental measures: this includes preventing exposure to potentially contaminated water, reducing contamination by rodent control and protection of workers in hazardous occupation. Measures should be taken to control rodents, proper disposal of wastes & health education etc.

vaccination• Immunization of farmers & pets prevent

disease. In some countries for instance Italy, USSR & China, where certain occupations carry a high risk of infections, vaccines are available.

• It is important that they should incorporate stains of the serotypes that predominant in the particular area since immunity to one type of leptospira may not protect against infection by another.

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PLAGUE• Plague is primarily and basically a zoonoses,

caused by Y. pestis, involving rodents and fleas. It exists in natural foci, and is transmitted by infected flea bites to human living or intruding into the same ecological environment. Plague occurs in many forms- enzootically, epizootically, sporadically and in epidemics of all types including anthroponotic and primary pneumonic forms.

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PROBLEM STATEMENT

• WORLD Plague is often seen as problem of the past or an

ancient disease that is unlikely to reappear. But continued outbreaks throughout the world attest to its tenacious presence. Although plague is predominantly a rural disease, there have been outbreaks among urban population in Madagascar and the United Republic of Tanzania.

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Cont..

• The data shows that from 2004 to 2009, a total of 12,503 cases of human plague, including 843 deaths, were reported by 16 countries in Africa, Asia and America. The global case-fatality rate was 6.7%.

• In 2004, India reported a localized outbreak of bubonic plague (8 cases and 3 deaths) in the Dangud village, District of Uttarkashi.

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EPIDEMIOLOGICAL DETERMINANTS

(a) AGENT : The causative agent, Y. pestis is a Gram-negative, non-motile, cocco-bacillus that exhibits bipolar staining with special stains ( Wayson’s stain). The bacilli occur in great abundance in the buboes, blood, spleen, liver and other viscera of infected persons, and in the sputum in cases of pneumonic plague.

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Cont..

(b) RESERVOIR OF INFECTIION : Wild rodents are the natural reservoirs of plague. These are found in mountains, deserts, cultivated areas and forests in temperate and tropical regions.

(c) SOURCE OF INFECTION : Infected rodents and fleas and case of pneumonic plague.

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Cont..

HOST FACTORS(a) AGE AND SEX : All ages and both sexes are susceptible.(b) HUMAN ACTIVITIES : Man may come into contact with

natural foci in the course of hunting, grazing, cultivation.

(c) MOVEMENT OF PEOPLE : Plague is associated with movement of people and cargo by sea or land. Rats and fleas are transported in this way.

(d) IMMUNITY : Man has no natural immunity. Immunity after recovery is relative.

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ENVIRONMENTAL FACTORS

(a) SEASON : Plague season starts from September until May. The disease tends to die out with the onset of hot weather.

(b) TEMPERATURE AND HUMIDITY : A mean temperature of 20 to 25 degree C and a relative humidity of 60% and above are considered favourable for the spread of plague.

(c) RAINFALL : Heavy rainfall, especially in the flat fields tend to flood the rat burrows.

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VECTORS OF PLAGUE• The commonest and the most efficient vector

of plague is the rat flea, X. cheopis, but other fleas may also transmit the infection, e.g X. astia , X. brasiliensis and Pulex irritants (human flea). Both sexes of the flea bite and transmit the disease.

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BLOCKED FLEA

• A flea ingest upto 0.5 cu.mm of blood which may contain as many as 5,000 plague bacilli. The bacilli multiply enormously in the gut of the rat flea and may block the proventriculus so that no food can pass through. Such a flea is called a ‘blocked flea’.

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FLEA INDICES

(a) TOTAL FLEA INDEX : the average number of fleas of all species per rat.

(b) CHEOPIS INDEX : the average number of X. cheopis per rat.

(c) SPECIFIC PERCENTAGE OF FLEAS : the percentage of different species of fleas that are found on rats.

(d) BURROW INDEX : the average number of free-living fleas per species per rodent burrow.

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HUMAN PLAGUE

MODE OF TRANSMISSION : There are atleast 5 basic types of transmission cycles in plague.

1. Commensal rat rat fleas man.2. Wild rodentswild rodent fleas or direct contactman.3. Wild rodents, predomestic rodents, commensal

rodentswild rodent fleas, predomestic rodent fleas, commensal rodent fleas man.

4. Manhuman fleasman.5. Manman.

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DISEASE IN MAN(a) Bubonic plague : most common type of the disease. The

infected rat fleas usually bite on the lower extremities and inoculate the bacilli. The bacilli are intercepted by the regional lymphatic glands where they prolifetare. Incubation period-2 to 7 days.

(b) Pneumonic plague : Primary pneumonic plague is rare. Pneumonic plague is highly infectious and spreads from man to man by droplet infection. Incubation period – 2 to 7 days.

(c) Septicaemic plague : Primary septicaemic plague is rare except for accidental laboratory infections. Incubation period- 1 to 3 days.

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LABORATORY INVESTIGATIONS

(a) Staining : it is important to prepare smears of the clinical materials (e.g. bubo fluid, sputum)

(b) Culture : blood for culture should be collected from all patients.

(c) Serology : acute and convalescent specimens of blood sera should be collected for antibody studies.

(d) Other methods : these include inoculation of guinea pigs or mice or immunofluorescent microscopic test.

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PREVENTION AND CONTROL

1) Control of cases (a) Early diagnosis- it is essential that plague-suspected

humans and rodents be examined bacteriologically to confirm the presence of plague.

(b) Notification- If a human or rodent case is diagnosed, health authorities must be notified promptly.

(c) Isolation- all patients with pneumonic plague should be isolated.

(d) Treatment- must be started without waiting for confirmation of the diagnosis.

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Cont..

2) Control of fleas The most effective method to break the chain of

transmission (rodentfleaman) is the destruction of rat fleas by the proper application of an effective insecticide.

3) Control of rodents Continuous mass destruction of rodents is an

important plague-preventive measure.

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Cont..

4) Vaccination

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Cont..

5) Chemoprophylaxis Chemoprophylaxis is a valuable preventive

measure, highly recommended. It should be offered to all plague contacts, medical, nursing, and public health personnel exposed to the risk of infection. The drug of choice is tetracycline. For adults, the dose is 500 mg 6 hourly for 5 days.

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