Epidemiology of bacterial zoonotic diseases with their prevention and control
THEIR PREVENTION AND
• 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
• It is characterized by: enlarged spleen
irregular febrile attacks
with profuse sweating
• The disease may last for several days,months or
• 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
1. AGENT: the agents are small,gram negative
rod shaped,non-motile,non-sporing and
intracellular coccobacilli of the genous
Four species infect man:
(a) B.melitensis : most virulent and invasive
species; usually infects goats
(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 INFECTION
The reservoir for human infection are:-
disease of cattle.
• The infected animal excrete Brucella in
urine,milk,placenta,uterine and vaginal
• 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
• ENVOIRMENTAL FACTORS
Conditions favouring the spread of brucellosis are:
Absence of standards of hygiene
Overcrowding of herds
Lack of exposure to sunlight
Unhygienic practices in milk and meat
Highly variable,usually 1-3 weeks,but may last for
6 months or more.
ROUTES OF TRANSMISSION
• Oral : unpasteurised milk & products, raw milk or
• Respiratory: lab workers.
• Skin: accidental penetration or abrasion
– - at risk farmers & veterinarians.
• Other routes:
Conjunctival, Blood transfusion, Transplacental,
person to person.
PATTERN OF DISEASE
• It may vary from an acute febrile disease to a chronic low
• The acute phase is characterized by:
pyrexia(up to 40-41deg c)
rigors and sweating
arthritis/arthralgia involving larger
low back pain
spleenomegaly and hepatomegaly
If patient is treated with tetracycline,the symptoms may
disappear quickly ,but infection ,being intracellular,may
persist giving rise to subacute or relapsing disease. 11
CONTROL OF BRUCELLOSIS• IN THE ANIMALS
The 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
(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
• 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
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
persons at risk should observe high standards of personal
They should wear protective clothing when handling
Exposed areas of skin should be washed and soiled clothing
(d)VACCINATION : human live vaccine of B.abortus strain
19-BA is available.
BRUCELLOSIS WOULD DISAPPEAR IF IT WERE ERADICATED
The national and international centre for brucellosis is
located at FAO/WHO Brucella reference centre, Indian
veterinary research institute ,Izatnagar,(Uttar Pradesh).15
• 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.
• 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
AGENT:- 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.
• 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.
• From an epidemiological point of view,
salmonellae can be classified into three main
(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.
RESERVOIR AND SOURCE OF INFECTION:-
Foods of animal origin, particularly commercially prepared
foods such as meat, poultry and egg products are
considered to be primary sources of salmonellosis.
Animals are the hosts and the principal vectors of zoonotic
salmonellosis. E.g cattle, swine, rodents etc.
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).
• Clinically, the disease may be manifest by one of the
(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
(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
Leptospirosis 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
(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.
(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.
• 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
• 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
• 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
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
• 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
• 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
• 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 .
(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.
• 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
• 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.
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.
• 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.
(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
(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.
(a) AGE AND SEX : All ages and both sexes are
(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.
(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.
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.
• 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’.
(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.
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
3. Wild rodents, predomestic rodents, commensal
rodentswild rodent fleas, predomestic rodent
fleas, commensal rodent fleas man.
4. Manhuman fleasman.
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.
(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
(d) Other methods : these include inoculation of
guinea pigs or mice or immunofluorescent
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
(d) Treatment- must be started without waiting for
confirmation of the diagnosis.
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.
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.