Plague is caused by the bacterium Yersinia pestis and is transmitted between rodents and humans via flea vectors. Rodents like rats and gerbils serve as reservoirs for the plague bacterium. Fleas become infected by feeding on infected rodents and transmit the bacterium to other rodents or humans during subsequent blood meals when they attempt to feed but cannot due to blockages in their digestive tract. There are three main forms of plague - bubonic, septicemic, and pneumonic - with pneumonic plague being able to spread from person to person. Historically, plague pandemics have contributed to major population declines and changes in societies.

1. ROLE OF VECTORS & ANIMAL
Reservoir IN TRANSMISSION OF
PLAGUE
Presented by :
ANIL
KUMAR
M.Sc. PHE IIND

2. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
INTRODUCTION
Plague is a zoonotic disease caused by highly virulent bacteria Yersinia
pestis.
Distribution of plague is worldwide maintained by wild rodents and
their fleas in the natural foci and localized infection.
Disease takes three main forms: Bubonic, Septicemic and Pneumonic.
Untreated bubonic plague can lead to secondary pneumonic stage
with 100% mortality.
Plague has lead to three pandemics.
 Yersinia pestis bacteria can also be used as biological weapon.
WHO identify plague as emerging disease.

3. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
HISTORY
540-750 AD: Justinian’s plague
50% - 60% people died of Rome along with the death of rats
Fall of the Roman Empire
1346-1400 AD: Black Death pandemic
Quarantine
~30 million European population died
Fall of the feudal system
1660 : Great Plague of London
1865 : Third epidemic in China and India
12 million people died
1894 : Alexandre Yersin and Shibasaburo Kitasato independently find the plague
bacterium in samples from humans and rats during the Hong Kong epidemic
1895 : Wild rodents are confirmed as hosts of plague when wild marmots in Mongolia
and Russia are found infected.
1896 : Waldemar Haffkine develops a partially effective heat-killed vaccine and uses it
during an outbreak in Bombay.
1897 : Yersin proposes a link between rats and plague
1905 : William Glenn Liston provides proof of fleas as the vector of plague.
1914 : Charles James Martin and William Bacot describe transmission of Y. pestis by
rat fleas, Xenopsylla cheopis, with blocked foreguts.

5. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Taxonomical hierarchy of Yersinia
KINGDOM : Eubacteria
PHYLUM : Proteobacteria
CLASS : Gammaproteobacteria
ORDER : Enterobacteriales
FAMILY : Enterobacteriaceae
GENUS : Yersinia
SPECIES : pestis, enterocolitica, pseudotuberclosis

6. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Characters of Yersinia pestis
• Gram –negative
• Non-motile
• Non spore forming
• Coccobacillus
• Size : 0.5-0.8 μm(diameter)
1-3 μm(long)
• Optimum temp: 28-30°C
• Optimum pH : 7.2-7.6 (extreme 5-9.6)
• Cell wall : lipopolysaccharide and enterobacterial antigen
• Obligate parasite
• By developmental mutational changes and gain of two plasmids
from Y. pseudotuberclosis and its progenitor Y. enterocolitia it
become more virulent and able to cause disease.
• Three biovars present : ribotype O/Antiqua, mediaevalis ribotype O
and ribotype B/Orientalis (based on their convesion of nitrate to
nitrite and fermentation of glycerol)

7. DISTRIBUTION
ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Group Number of species
Rodents More than 200
Carnivores 20
Lagomorphs 14
Insectivores 4
Artiodactyla 3
Primates 2
Marsupials 2
Animals naturally infected with Y. pestis
(Data represent relative number of species in each
group and may not include all species ever found
to have been infected : Poland and Barnes, 1979;
Pollitzer,1954)

8. Region Animal resorvoir Primary vector
Common name Scientific name Common name Scientific name
INDIA
Indian gerbil Tatera indica Rat fleas Xenopsylla cheopis
Rat Rattus rattus Gerbil fleas Xenopsylla astia
Nosopsyllus punjabensis
Bandicoot rat Bandicota bengalensis
Bandicota indica
Metad Millardia meltada
Indian field
mouse
Mus booduga
Spiny field
mouse
Mus platythrix
Indian bush rat Golunda ellioti
Palm squirrel Funambulus species
ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Major wild rodents and flea vectors of natural foci
*Sentinal animal :

9. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Indian gerbil Millardia meltada Rattus rattus
Golunda ellioti

10. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE

11. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Cases and Deaths due to Human Plague in India
Year Place Cases Deaths
1963 Throughout India 197 22
1964 Penninsular India 106 13
1965 -do- 1 0
1966 -do- 46 2
1967-1993 - Nil Nil
1994 Maharashtra/Gujarat 876 54
1995-2001 Nil Nil
2002 Simla Dist.Himachal
Pradesh
16 4
2003 Nil Nil
2004 Uttar Kashi
Dist.Uttarakhand
8 3
2005-2015 - Nil Nil

12. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Fleaborne transmission
Direct/physical contact with infected animal/human
Ingestion of infected animal
Inhalation of infectious droplets from animals or humans
Different
routes of
transmission
of
Y. Pestis
to humans
TRANSMISSION

13. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Flea borne transmission of Y. pestis
Day 0
Flea become
infected by
feeding on
mammal host
with bacterial
load of at least of
10000 CFU/ml.
Day 1-4
Some sps of
fleas are able
to transmit Y.
pestis after 3
hours of
getting
infection,
known as
Early-Phase
transmission
Day 5 – later
In some sps of fleas Y. pestis
accumulate in the midgut
and gradually extend into
the proventriculus. The
bacteria produce a biofilm
to adhere to the surface of
the spines, enabling them
to resist being pumped into
the midgut. This blockage
prevents ingested blood to
enter in flea’s stomach.
Thus starving flea tries to
feed, blood taken in mixes
with the Y. pestis and it
regurgitated back on the
mammalian host.
Mammal to fleas
* Y. pestis from bite site
it travels to lymphatic
system where it
multiplies and spread
throughout the body
and cause bubonic
plague.
*untreated cases may
lead to pneumonic
plague.
*uninfected fleas comes
in contact with these
mammals they got the
infection.

14. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Genes responsible for infection
transmission in fleas
Hms
Pgm
ymt
 Murine toxic(ymt):
for enhancing the survival rate of Y.
pestis (all gram negative) in fleas midgut.
 Pigmentation locus(Pgm) :
responsible for dense colonies of Y.
pestis and its blockage in proventriculus
and iron uptake.
 Hemin storage locus(Hms) :
it enables Y. pestis to synthesise
biofilm which allows dense colony growth
in proventriculus and resist it from going to
the midgut.

15. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
TRANSMISSION CYCLE
The Y. pestis transmission cycle and the progression from bubonic plague to pneumonic plague in humans. Y.
pestis is transmitted between rodent hosts and flea vectors in two cycles: domestic and sylvatic. Humans can
become infected by flea bites or by direct contact with infected rodents and other animals. Pneumonic plague can
be transmitted person-to-person. Solid lines: common routes and dashes occassional routes.

16. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
EXAMPLE:
Damaged grain storage or
garbage will attract rodents and
animals
Domestic animals may be affected by infected fleas
and may pass the infection to humans
Rat fall indicate the epizootic of plague

17. ROLE OF VECTORS AND ANIMAL RESORVOIR IN TRANSMISSION OF PLAGUE
Continued…
Infected fleas jump to humans in search of bloodmeal.
People will develop bubonic plague after bittten by
infected flea
Pnemonic plague spreads person-to-person
through inhalation of infectious droplets

18. Reference
s : Plague by Rachel C. Abbott and Tonie E. Rocke , National
Wildlife Health Centre, Circular 1372, US department of
Interior and US department of geological survey,2012
Robert D. Perry and Jacqueline D. Fetherston, Yersinia
pestis – Etiology Agent of plague, Clinical Microbiology
Reviews, Jan. 1997, p. 35-66., Vol 10(1)
Angela Clem and S Galwankar., plague: A Decade Since
the 1994 Outbreaks in India , JAPI, Vol. 53., May 2005
Plague, N. Balakrishnan., National Centre for Disease
Control