Can you see something on the screen. Enemy’ size (Vector & microbes they carry) may not determine the potential of its threat always.
Vectors shouldn’t be thought of as mere dumb vessels or flying hypodermicneedles. It is helpful to think of them as tiny, well-programmed robots.
The Black Death, decimator of Europe, killer of tens of millions worldwide is the work of a tiny flea vectoring the bacilli that cause bubonic plague from rats to people.
The arthropods are by far the most successful phylum of animals, both in diversity of distribution and in numbers of species and individuals. They have adapted successfully to life in water, on land and in the air.
Malaria parasites in human blood - Laveran, 1894- Ross, 1897Transmission of bird malaria by Culex mosquitoes - Ross, 1898Complete development of human malaria parasite in mosquitoes - Grassi, 1898Transmission of human malarial parasite by mosquitoes - Sambon and Low, 1899Only Anopheles mosquitoes transmit human malarial parasites - Watson and Christophers, 1899
History of VBDs continues to evolve not only due to new agents being discovered but also due to Changing epidemiology of VBDs and adaptation and evolution of the vector due to ecological pressures.
Malaria has shaped the course of history for millennia. It has always been part of the ups and downs of nations; of wars and of upheavals. Kings, popes, and military leaders were struck down in their prime by malaria.Alexander the Great, conqueror of many nations, was vanquished by the bite of a tiny mosquito bearing malaria parasites in the marshes of what is now called Iraq.
These aresome statistics from different wars highlighting the contribution made by VBDs to the burden of Non- Battle casualties. The Malaria and typhus fevers being major problems of the soldiers. The history of many campaigns would have been different but for malaria.
Now we shall see some basic concepts related to VBDs.
The defining characteristic of a vector-borne infection is its high transmissibility.Vectors help pathogens bridge the gap from a diverse array of host animals (mice, rats, monkeys, birds, prairie dogs, pigs, etc.) to humans.Vectors generally don’t become “ill” from carrying their various viral, protozoan and nematode infections. They might accrue some damage to their tissues, but in some cases this “damage” actually makes them more likely to transmit and infect. A mosquito with problems in its feeding apparatus will need to take additional bites to complete a blood meal. A flea with a gut clogged with plague bacteria will regurgitate more.
Most vectors are arthropods which have the characteristics as given on slide.
Head is a multifunctional unit in insects responsible for feeding, sensory inputs and nervous system.
ASSOCIATION Demonstrate feeding or other effective contact with host.2. SPECIFIC CONNECTION A convincing biological association in time and/or space of suspected arthropod and host with occurrence of clinical or subclinical infection of host.3. TRANSMISSION Ability to transfer infectious agent under controlled conditions.4. BIOLOGICAL GRADIENT Low and high populations of suspect vector results in low and high cases in susceptible hosts, respectively.
When can an Arthropod function as a vector.
Blood meals provide an arthropod with nutrients necessary for the metabolism, metamorphosis, and reproduction
The reproductive cycle of an arthropod is called its gonotrophic cycle.
Propagative transmission-organism undergoes a change in its numbers, i.e. amplification only in the body of the vector. (e.g. viruses, YF, WNV, EEE, etc.)Cyclo-developmental transmission-organism undergoes cyclical change but does not multiply. (e.g. Wuchereriabancrofti-Bancroftianfilariasis)Cyclo-propagative transmission-organism undergoes a cyclical change and multiplies.(e.g. malaria, Chagas)
Transstadial transmission:sequential passage of parasites from one life stage to next when it occurs from adult to egg called: transovarial transmissionalso termed transgenerationalvenereal transmission: occurs as a result of passage of parasites between male and female vectors. RARE
In an era of NCDs like CHD, DM, HTN which our colleagues in the clinics so fondly talk of, why should we in the field of Public Health be harping on VBDs. Malaria has reduced, Typhus has come down, so many infections can now be prevented by a shot of vaccine. There are a number of reasons to explain our concern.
The toll from other vector-borne diseases like trypanosomiasis, leishmaniasis, Japanese encephalitis, onchocerciasis and yellow fever add more millions of cases each year.
If only mortality due to VBDs was not enough, these VBDs can put humans through lifelong suffering.
Filariasis is one such disease. Can you name another dreaded disease though not a VBD ------Leprosy.
The Dengue virus continues to spread its area of influence relentlessly, thanx to our indiscriminate urbanisation and use of disposable containers which we tend to throw around so carelessly.
Malaria was, is and will continue to be with us for ages to come. Malaria has reminded us of our limitations in our abilities to combat this tiny but very powerful adversary in hsitory of Public health.
The National Vector Borne Disease Control programme (NVBDCP) is providing 100% centralassistance to the seven North Eastern states for malaria control activities including provision ofmanpower, bed nets and spray wages. The Enhanced Malaria Control Project (EMCP) with WorldBank assistance was implemented during 1997-2005 in 100 districts of eight high malaria incidencestates. The World Bank is assisting the programme again through the National Vector BorneDisease Control Project (2008-2013) which was launched in September 2008. The IntensifiedMalaria Control Programme (IMCP) funded by Global Fund to Fight AIDS, Tuberculosis and Malaria(GFATM) is in operation since 2005 in 106 districts of 10 states. These projects provide special inputs in these areas in the form of Rapid Diagnostic Tests (RDTs), Artesunate CombinationTherapy (ACT), Insecticde Treated Bednets (ITNs) and Health Systems Strengthening (HSS).
Insecticide resistance has been a problem in all insect groups that serve as vectors of emerging diseases. Although mechanisms by which insecticides become less effective are similar across all vector taxa, each resistance problem is potentially unique and may involve a complex pattern of resistance foci. The main defense against resistance is close surveillance of the susceptibility of vector populations.
Ever since the discovery of the first case of chloroquine resistance along the Thai-Combodian borderin the late 1950s, Southeast Asia has played an important role as a focus for the development of drugresistance in Plasmodium falciparum. Molecular markers for antimalarial resistance have been identified, including pfmdr-1 and pfcrt polymorphisms associated with chloroquine resistance and dhfr and dhps polymorphisms associated with SP resistance. The dihydrofolatereductaseinhibitors include proguanil, chloroproguanil, pyrimethamine and trimethoprime and sulfa drugs like dapsone, sulfalene, sulfamethoxazole and sulfadoxine. In India chloroquine resistance was first detected in 1973 in Karbi-Anglong district in Assam19 and in 1974 in Nowgong district of Assam. Gradually it has spread towards the west and south, covering almost the entire country. Resistance to SP was first described from theThai-Cambodian border in 1960s. Resistance in P. falciparum to SP combinationwas first detected in Delhi in 1987. Mefloquine resistance was first observed in late 1980snear the Thai-Cambodian border It is frequent in some parts of Southeast Asia. Resistance in P. falciparum to mefloquine in India was detected in Surat district in Gujarat state. .
This slide shows the change in temp all over the world. Different lines represent isotherms.
IPCC, 2007: Climate Change 2007: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change.
Stockholm International Peace ResearchInstitute (SIPRI) published a meticulous analysis of themost likely pathogens to be developed as biologicalweapons (Geissler, A New Generation of BiologicalWeapons) .
vector borne diseases-ASK
"India lives in its villages"
Why we took more than 60 years to realize the value of
health of rural India (NRHM )
EPIDEMIOLOGY OF VBDs
Enemy’ size -------------------- potential of its threat
570 million years
SCHEME OF PRESENTATION
BASIC CONCEPTS IN VBDs
WHY VBDs SHOULD CONCERN US
CLIMATE CHANGE & VBDs
CHALLENGES IN VBDS
WORST SCOURGES OF MANKIND
THREAT TO HUMAN SURVIVAL
KILLED MORE MEN THAN ALL THE WARS
CAHNGED THE COURSE OF HISTORY
History of Medical Entomology:
• References to associations between humans
and arthropods – historical
(Homer and Aristotle, among others, wrote about the nuisance caused
by flies, mosquitoes, lice and/or bedbugs.)
• Important discoveries:
•1700’s - Microscope - Leeuwenhoek
•1800’s - Infectious Disease - Koch et al.
History of Medical Entomology
• 1877- Manson, --Mosquitoes (Culex pipiens) and filarial
worms (Wuchereria bancrofti) • 1891 - Smith & Kilborne, -Tick (Boophilus annulatus) and
Texas cattle fever (piroplasmosis) transmission • 1900- Finlay, Reed, Carroll, Agramonte and Lazear,
Mosquito (Aedes aegypti) and yellow fever virus • 1895- Bruce- Trypanosomes in cattle blood -
History of Medical Entomology –:
• Laveran – MP in blood
• 1896- Bruce, Tsetse fly (Glossina sp.)
transmission of trypanosomes • 1903- Bruce, Tsetse fly transmission of
trypanosomes to humans (African Sleeping
• Ronald Ross - Anopheles mosquitoes with
History of Medical Entomology - :
• Graham, 1902-- Mosquito transmission of dengue virus • Liston, Verjbitski et al., --1895 – 1910-- Fleas and plague • Chagas, 1908--Triatomine bugs and trypanosomes (Chagas
disease) • Blalock, 1926--Black flies and onchocerciasis (river blindness)
• Mosquitoes and viral encephalitides - Hammon and Reeves,
• Ticks and Lyme disease - Spielman, early 1960’s
>10000 years ago Malaria in Africa
19th Century AD- Malaria almost all over the globe
Early 20th Century AD- Millions die of malaria
almost all over the world
Early 1950s - Malaria almost disappears from North
America and from almost all of Europe; deaths mainly
1960-70s: Malaria strikes back with vengeance
MALARIA & WARS
"The history of malaria in war
might almost be taken to be the
history of war itself
Col. C. H. Melville, Professor of hygiene, Royal Army Medical College, London (1910) in
Ronald Ross's book The Prevention of Malaria.
Cause of Deaths in War
Battle Injuries (BI)
Civil War (Union)
World War I
World War II
Military Entomology - World War I
By World War I, the connection between insects
and disease was well established.
Entomologists (6-8) were commissioned as officers
in the Sanitary Corps.
Over 9,600 cases of malaria occurred in troops
training in the southern U.S.
Trench fever and louse-borne typhus were the
primary arthropod-borne diseases in Europe as
troops were often infested with lice.
SCHEME OF PRESENTATION
BASIC CONCEPTS IN VBDs
WHY VBDs SHOULD CONCERN US
CLIMATE CHANGE & VBDs
CHALLENGES IN VBDS
HOST ANIMALS -----VECTOR-----HUMANS
VECTORS DON’T BECOME “ILL”
Phylum Arthropoda :• Bilaterally symmetrical
• Jointed legs
• Dorsal heart – open circulatory system
• CNS (organized central nervous system)
• Striated muscle
Class Crustacea - lobsters, crabs, etc.
Class Chelicerata - spiders, mites, ticks, scorpions,
Class Diplopoda - millipedes
Class Chilopoda - centipedes
Class Insecta - beetles, flies, moths, mosquitoe.
THREE distinct body regions:
- Head (feeding, sensory, CNS)
- Thorax (locomotion, respiration)
- Abdomen (feeding, reproduction)
Arthropods & Health
• Direct Causes of Disease or Distress
• Vectors or Hosts of Pathogenic
• Natural Enemies of other medically
INCRIMINATING A VECTOR
Must be susceptible to infection by pathogen.
Live long enough for pathogen to complete
multiplication or development.
THIS AFFECTS THE transmission rate in nature.
COMPONENTS OF TRANSMISSION CYCLE
• A vector must take at least 2 blood meals during
its lifetime to transmit a parasite.
• Once to acquire the infection.
• Second to transmit parasite.
This includes the sequence of 5 steps :
1. searching for a host (questing)
2. blood feeding
3. blood meal digestion
4. egg maturation
ARTHROPOD ACQUISITION & DEVELOPMENT
(SALIVARY GLANDS, or
PATHOGEN PASSAGE THRU
GUT WALL OR EPITHELIAL
PATHOGEN TRANSPORT BY
HEMOLYMPH TO TISSUES OF
Suitable host must be found:
Anthropophagic (feed on humans only)
endophilic (inside loving)
exophilic (outside loving)
Zoophagic (feed on vertebrates other than humans)
ILLUSTRATION EXTRINSIC & INTRINSIC
Mosquito refeeds /
Mosquito feeds /
PATHOGEN DEVELOPMENT IN BODY OF
• Propagative transmission- (e.g. viruses, YF, WNV,
• Cyclo-developmental (e.g. Wuchereria bancroftiBancroftian filariasis)
• Cyclo-propagative transmission-. (e.g. malaria,
PATHOGEN ACQUISITION BY HOST
HOST INGESTS OR
BACK PRESSURE DIGESTIVE
ESCAPE THROUGH BODY WALL
INFECTIVE FLUIDS FROM
GLANDS (e.g. tick coxal glands)
MODES OF TRANSMISSION
Passage of parasites/pathogens from one life stage to next
life stage or generation to generation.
MODES OF TRANSMISSION
Passage of parasites/pathogens between vector
“Bridging” mosquito species in yellow fever
another infected mosquito species
transmits pathogen now to humans
Vectorial Capacity is thus, a function of
(a)the vector's density in relation to
its vertebrate host,
(b) the frequency with which
it takes blood meals on the host species,
(c)the duration of the latent period in the
(d) the vector's life expectancy.
FACTORS THAT STRONGLY AFFECT
PATHOGEN TRANSMISSION BY VECTORS
Vector competence (ability to get infected & transmit)
Incubation period in vector (influenced by temperature)
Vector contact with critical host
Population abundance of vector & hosts
Diurnal feeding habits of vector
Pathogen replication in host
Host feeding preferences
Precipitation – flooding & drought
Proximity of vectors/reservoirs to human populations
Mosquitoes and Key VBDs
Responsible for a great VBD burden
Malaria – parasite
Yellow fever – virus
Dengue fever/hemorrhagic fever – virus
Other viral fevers
West Nile, Rift Valley, Bunyamwera
Filiariasis – helminth
Encephalitis – viruses
Western Equine, Eastern Equine, St. Louis, etc.
Fleas and VBDs - Plague
Plague: Pasteurella (now Yersinia) pestis
Historically, a cause of major epidemics and
Now readily controllable with antibiotics
Concern as a bioterrorism agent
Why should we be concerned ?
These diseases represent 17% of the global disease
300 million malaria cases (WHO, 2009a),
50–100 million dengue cases (WHO, 2009b),
120 million filariasis cases (WHO, 2000).
Every year, 500 million people become severely ill with
causes 30% of Low birth weight in newborns Globally.
>1 million people die of malaria every year. One child dies
from it every 30 seconds
40% of the world’s population is at risk of malaria. Most
cases and deaths occur in SSA.
Malaria is the 9th leading cause of death in LICs and MICs
11% of childhood deaths worldwide attributable to malaria
SSA children account for 82% of malaria deaths worldwide
Why worry about vector-borne diseases?
Negative impact on commerce, travel, & economies
(e.g., Rift Valley fever, yellow fever)
Explosive debilitating outbreaks (e.g., yellow fever)
Poorest are worst affected – min access to health care
Preventable cause of human illness & death
Charrel et al. 2007. N Engl J Med 356;8
How Env change affects VBDs?
Dr. Paul Reiter:
“The natural history of mosquito-borne diseases is
complex, and the interplay of climate, ecology, vector
biology, and many other factors defies simplistic
Environmental Health Perspectives, Vol. 109, 2001. pp. 141-161.
Human-Driven Ecological Changes that alter
Incidence of Mosquito-Borne Diseases
Large-scale water projects
Global climate change
Industrial agriculture practices
Industrial animal husbandry practices
Widespread use of pesticides
Introduction of exotic species
Tendency towards monoculture
The combination of increasing population and resource consumption, along with waste
generation, drives the regional environmental change typically indicated by trends in land
use and land cover change. Three characteristic processes occur in relation to land use:
urbanization, agricultural intensification (including food production and distribution)
and alteration of forest habitat which drives disease emergence.
Global Climate Change
+ 8 - 16 C
Interactive map: www.actoncopenhagen.decc.gov.uk
Source: Met Office Hadley Centre
What diseases are the most
effects of storms
air pollution effects
Hypothesis: global warming will increase the incidence
of vector-borne infectious diseases
“Bugs” like warmth
Vector-borne diseases don’t occur much in winter, or in
the Arctic or Antarctic, or on high mountains.
Environment and Exposure
Where might Climate Impact?
Environment and Exposure
Where might Climate Impact?
Most arboviral diseases
increases in global temperatures,
more frequent extreme weather events,
warmer winters and evenings
Other cofactors (biodiversity loss, urbanization)
opportunity for increased distribution,
expanded breeding, prolonged mosquito
incubation period .
Increased Malaria Risk
The IPCC has noted that the global population at risk
from vector-borne malaria will increase by between
220 million and 400 million in the next century
While most of the increase is predicted to occur in
Africa, some increased risk is projected in Britain,
Australia, India and Portugal
FACTORS CONTRIBUTING TO EMERGENCE OR REEMERGENCE OF INFECTIOUS DISEASES
Resistance of the vectors of vector-borne
infectious diseases to pesticides.
Immunosuppression of persons due to medical
treatments or new diseases that result in infectious
diseases caused by agents not usually pathogenic
in healthy hosts.(e.g. leukemia patients)
Of the 22 prime candidates, half were arthropod-borne
Lockwood JA. Six-Legged Soldiers: Using Insects as Weapons of War.
Oxford University Press, Inc., New York, 2009, pp 400.
Land use and
Modified from Sutherst R.W. Clin Micribiol Rev 2004;17:136-73
Areas affected by Malaria – Env change
P. falciparum proportion
Paradigms – Border, Project, Migrant, Tribal
Epidemics of VBDs - Dengue
Diagnostics- Microscope to RDTs
Treatment- Chloroquine to ACT
Resistance – reported and rising
Prevention – IRS to LLINs
Control - Eradication - Control
RS & GIS – Surveillance