REVIEW

Dengue and Other Viral Hemorrhagic Fevers in India

Shally Awasthi • U. C. Chaturvedi

Received: 16 September 2011 / Accepted: 14 November 2011 / Published online: 18 January 2012

� The National Academy of Sciences, India 2012

Abstract The important viral hemorrhagic fevers (VHF)

in India spread by an arthropod vectors are Dengue fever/

Dengue haemorrhagic fever and Kyasanur forest disease.

Another VHF is caused by Hanta virus infection and for this

there is no known vector. The diagnosis of VHF is based on

typical clinical presentation and thereafter confirmed by

detection of either virus or viral RNA or by demonstration of

a rise of antibody titres against it. Treatment is by and large

symptomatic as there are no specific drugs available against

the viruses. Dengue fever has acquired epidemic magnitude

in certain parts of India and has about 10% mortality.

Research is going on for the development of effective vac-

cines against Dengue fever. The principles of primary pre-

vention of vector borne diseases is through vector control

measures, elimination of breeding sites in and around human

dwellings and personal protection against vector bite.

Keywords Hemorrhagic fevers � Dengue �Kyasanur forest disease � Virion � Hantaviruses

Introduction

Viral hemorrhagic fevers (VHF) are a distinct group of acute

viral infections which result in severe multisystem syndrome

due to wide spread damage to the vascular system. This

results in varying degree of hemorrhage, including con-

junctivitis, petechia, ecchymosis and shock, sometimes

leading to death. Hemorrhagic fever viruses belong to four

taxonomic families (Table 1), all being single-stranded

RNA viruses and possess a lipid envelope [1].

Flaviviridae

Dengue virus, Yellow fever virus, Omsk hemorrhagic fever

virus, Kyasanur forest disease virus.

Epidemiology/Geographic Distribution

Flaviviridae include Alkhurma HF virus, Kyasanur forest

disease, and Omsk HF. Alkhurma HF virus is a variant of

Kyasanur forest disease virus found in Saudi Arabia and

reported in a small number of patients since 1990s [2].

Yellow fever virus is found throughout sub-Saharan Africa

and tropical South America but its activity is intermittent and

localized [3]. The annual incidence is believed to be about

200,000 cases per year globally. Case fatality rate ranges

greatly depending on the epidemic but may reach up to 50%

in severe yellow fever cases. Dengue virus is found

throughout the tropical Americas, Africa, Australia, and

Asia. Case fatality rate for DHF is generally low 1–10%

depending on available treatment [4]. Kyasanur forest virus

is confined to Mysore state of India but spreading. Case

fatality rate is 3–5%. Omsk Hemorrhagic fever virus is still

isolated to the Omsk and Novosibirsk regions of the former

Soviet Union. Case fatality is 0.5–3%. The South American

HF has a case-infection ratio of more than 50% of those

exposed. The mortality rate is 15–30% (Table 1)1 [3, 4].

S. Awasthi (&)

Department of Pediatrics, CSM Medical University,

Lucknow, India

e-mail: shallya@rediffmail.com

U. C. Chaturvedi

201-Annapurna Apartments, No. 1, Bishop Rocky Street,

Faizabad Road, Lucknow 226 007, India

e-mail: uchaturvedi201@gmail.com 1 http://en.wikipedia.org/wiki/Flaviviridae.

123

Proc. Natl. Acad. Sci. Sect B. Biol. Sci. (January–March 2012) 82(1):69–80

DOI 10.1007/s40011-011-0006-9

Virion Structure

The virion of the Flaviviridae is spherical to pleomorphic

and the virions are enveloped. The virions are measured

40–50 nm in diameter. An envelope and a nucleocapsid are

present in the virion of Flaviviridae. The capsid is envel-

oped with glycoprotein peplomers. The surface projections

of the capsids are made up of small spikes that are sur-

rounded by a prominent fringe. The capsid has a polyhedral

symmetry and it is round. The capsid has an inner core

protein. The core is measured 20–30 nm in diameter, and it

is isometric2 [3–5] (Fig. 1).

Genome Structure

The genome of Flaviviridae consists of a linear, positive-

sense, single stranded RNA of about 11 kb in length, and

the genome is not segmented. The genome has a 50-end

which carries a methylated nucleotide cap or genome-

linked protein. The genome of Dengue virus consists of a

single stranded, non segmented, positive sense ribonucleic

acid (RNA). The genome is translated into a single poly-

peptide which is co- and post-translationally processed by

host signalases as well as the virus encoded serine protease

into the three structural (C, prM/M, and E) and seven non-

structural proteins (NS) in the order C–prM–E–NS1–

NS2A–NS2B–NS3–NS4A–NS4BNS5 that traverse the

endoplasmic reticulum membrane. The three structural

proteins, C–M–E, are located at the amino terminus, while

NS NS–NS2a, NS2b–NS3–NS4a, NS4b, and NS5 are at the

carboxy terminus [3–5].3

Replication

Replication of Flavivirus takes place in the cytoplasm.

Flavivirus cannot replicate in the nucleus because, like

Table 1 Viruses causing haemorrhagic fevers

Family/Viruses Diseases Transmission

to humans by

Incubation

period (days)

Geographical distribution

Flaviviridae

Yellow fever virus Yellow fever Mosquito 3–6 Tropical Africa, South America

DEN Dengue HF Mosquito 3–6 Asia, Americas, Africa

KFD virus KFD Ticks 2–7 India

Bunyaviridae

Phlebovirus Rift valley fever Mosquito 2–5 Africa

Nairovirus Crimean-congo HF Tick 3–12 Europe, Asia, Africa

Hantavirus HF with renal syndrome,

hantavirus pulmonary

syndrome

Rodent 9–35 Asia, Europe, worldwide

Arenaviridae

Lassa fever virus Lassa fever Rodent 5–16 Africa

Junin virus Argentine HF Rodent 7–14 South America

Machupo virus Bolivian HF Rodent 9–15 South America

Sabia virus Brazilian HF Rodent 7–14 South America

Guanarito virus Venezuelan HF Rodent 7–14 South America

Filoviridae

Marburg virus Marburg Unknown 3–16 Africa

Ebola virus Ebola Africa

Fig. 1 Virion structure of Flaviviridae [6]

2 http://en.wikipedia.org/wiki/Flaviviridae. 3 http://en.wikipedia.org/wiki/Flaviviridae.

70 Proc. Natl. Acad. Sci. Sect B. Biol. Sci. (January–March 2012) 82(1):69–80

123

most other RNA viruses, it uses the host cell’s RNA

dependent RNA polymerase to replicate. The genome

mimics the cellular mRNA molecule in all aspects except

for the absence of the poly-adenylated (poly-A) tail. This

feature allows the virus to exploit cellular apparatus to

synthesise both structural and NS, during replication. The

cellular ribosome is crucial to the replication of the flavi-

virus, as it translates the RNA, in a similar fashion to

cellular mRNA, resulting in the synthesis of a single

polyprotein. Once translated, the polyprotein is cleaved by

a combination of viral and host proteases to release mature

polypeptide products. Nevertheless, cellular post-transla-

tional modification is dependent on the presence of a poly-

A tail; therefore this process is not host-dependent. Instead,

the polyprotein contains an autocatalytic feature which

automatically releases the first peptide, a virus specific

enzyme. This enzyme is then able to cleave the remaining

polyprotein into the individual products. One of the prod-

ucts cleaved is a polymerase, responsible for the synthesis

of a (-) sense RNA molecule. Consequently this molecule

acts as the template for the synthesis of the genomic

progeny RNA. New viral particles are subsequently

assembled. This occurs during the budding process which

is also responsible for the accumulation of the envelope

and cell lysis [3–5] (Fig. 2).4

Bunyaviridae

Rift valley fever virus, Crimean-Congo hemorrhagic fever

virus, Hantavirus.

Epidemiology/Geographic Distribution

Bunyaviruses are seen throughout Africa, the Middle East,

the Balkans, southern Russia, and western China. RVF is

found primarily in sub-Saharan Africa and was recently

isolated in Saudi Arabia and Yemen in 2000. The case

fatality rate in humans is generally around 1%. CCHF is

found in most of sub-Saharan Africa, Eastern Europe and

Asia. The case fatality rate is 30% and nosoicomial out-

breaks have been documented through exposure to infected

blood products. Approximately 1% of individuals exposed

to RVF virus become infected, but the mortality rate of

persons infected is 50%. CCHF has an infection rate of

20–100% and a fatality rate of 15–30%. Hantaviruses are

divided into two groups based on location: Old world

viruses are found in eastern Europe and eastern Asia while

new world viruses are found in North and South America

[3, 4] (Table 1).5

Virion Structure

Bunyavirus virions have a complex structure. They consist

of an envelope and three nucleocapsids. Virions are

80–120 nm in diameter. The virions vary in shape from

spherical to pleomorphic. Surface projections are 5–10 nm

long spikes which evenly coat the surface. The nucleo-

capsids are elongated and have helical symmetry

[1, 5–7]6,7,8 (Fig. 3).

Genome Structure

The bunyavirus genome is monomeric and consists of three

segments (large (L), medium (M) and small (S)). Besides,

they exhibit a pseudo-circular structure due to each seg-

ment’s complementary ends. The L segment encodes the

RNA dependent RNA-polymerase, necessary for viral

RNA replication and mRNA synthesis. The M segment

encodes the two envelope glycoproteins which project

Fig. 3 Virion structure of Bunyavirus [49]

Fig. 2 Replication cycle of Flavivirus [7]

4 http://en.wikipedia.org/wiki/Flaviviridae.

5 http://en.wikipedia.org/wiki/Bunyaviridae6 http://en.wikipedia.org/wiki/Bunyaviridae.7 http://www.virology.net/Big_Virology/BVRNAbunya.html.8 http://microbewiki.kenyon.edu/index.php/Bunyaviridae.

Proc. Natl. Acad. Sci. Sect B. Biol. Sci. (January–March 2012) 82(1):69–80 71

123

from the viral surface and aid the virus in attaching to and

entering the host cell. The S segment encodes the nucleo-

capsid protein (N). The L and M segment are negative

sense. These RNA segments are single-stranded, and exist

in a helical formation within the virion. The entire genome

is about 10,500–22,700 nucleotides long [1, 5–7].9,10,11

Replication

Replication begins with the attachment of viral proteins to

host receptors and entry of virus by endocytosis. Acidifi-

cation of endocytic vesicles causes uncoating of the virus

which is followed by fusion of viral membranes with that

of the host endosomes. Primary transcription of viral

complementary mRNA occurs and the L, M and S mRNAs

are translated. This is followed by RNA replication and

morphogenesis. Mature virions are released by fusion of

virus-containing cytoplasmic vesicles with the plasma

membrane and budding [1, 5–7]12,13,14 (Fig. 4).

In India, cases of VHF belong to the family of Flavi-

viridae, which includes Dengue virus and Kyasanur forest

disease virus. There have been recent reports of emerging

public health threats due to Hantavirus, belonging to the

family Bunyaviridae. Studies have been done in India to

look for Nairovirus which causes Crimean-Congo haem-

orrhagic fever but no conclusive evidence is found; neither

in human sera nor in the vector. Table 2 below summarizes

the reservoirs and modes of transmission of hemorrhagic

fever viruses reported from India [1, 3] (Table 3).

Dengue and Dengue Hemorrhagic Fever

Dengue has been recognized since the latter part of the 18th

century as causing epidemics in tropical and subtropical

regions globally. Some 2,500 million (2.5 billion) people

are estimated to currently be at risk of dengue in over 100

countries across the globe. It is estimated that between 50

and 100 million cases of dengue fever, 500,000 cases of

dengue hemorrhagic fever/dengue shock syndrome (DHF/

DSS) and more than 20,000 deaths from DHF/DSS occur

each year [3, 4]. Dengue virus (DEN) is a small single-

stranded RNA virus comprising four distinct serotypes

(DEN-1 to -4). These closely related serotypes of the DEN

belong to the genus Flavivirus, family Flaviviridae [8].

Humans are the only vertebrate hosts of the virus. There

is a jungle cycle between monkeys and mosquitoes, but this

plays no role in human disease (Fig. 5).

The virus is transmitted when a mosquito of the genus

Aedes bites an individual infected with DEN. The virus in

the blood of the infected individual then infects the mos-

quito and travels from the mosquito’s stomach to its sali-

vary glands where the virus multiplies. The virus is then

injected into another person, when the mosquito injects

anticoagulants that prevent blood clotting when the mos-

quito is feeding. The mosquito remains capable to transmit

dengue for its entire life. There is an enzootic dengue

transmission cycle in the forest involving Aedes mosqui-

toes and lower primates in Africa and Asia [9] (Fig. 6).

Aedes aegypti breeds in fresh water and particularly in

manmade containers such as old tyres, pot plant holders,

buckets and tree hollows in urban areas. Aedes albopictus

is a mosquito common in South East Asia and Papua New

Guinea and can also be an important vector. Other Aedes

species are involved in the enzootic monkey cycle. There is

no evidence of person to person transmission [4].

Dengue fever (break bone fever) classically presents as

an acute febrile illness. The incubation period is usually

short but varies from three to 14 days. It is extremely

debilitating with fever lasting 3–5 days, myalgia (particu-

larly backache), arthralgia, retro-orbital pain, anorexia,

gastrointestinal disturbance, rash and increased vascular

permeability. There is a high subclinical rate of milder

disease in children compared to adults and a low fatality

rate. Recovery from infection with one serotype of the

DEN results in homologous immunity but does not provide

protection against infection with other serotypes [3].15

DHF is a severe complication of DEN infection. It

occurs mainly in children and is characterized by abrupt

onset of fever, haemorrhagic phenomena and thrombocy-

topaenia. In its severest form it may result in shock (DSS),

Fig. 4 Replication cycle of Bunya virus (http://www.access

excellence.org/RC/VL/GG/influenza.php)

9 http://en.wikipedia.org/wiki/Bunyaviridae.10 http://www.virology.net/Big_Virology/BVRNAbunya.html.11 http://microbewiki.kenyon.edu/index.php/Bunyaviridae.12 http://en.wikipedia.org/wiki/Bunyaviridae.13 http://www.virology.net/Big_Virology/BVRNAbunya.html.14 http://microbewiki.kenyon.edu/index.php/Bunyaviridae.

15 http://ci.vbi.vt.edu:13001/pathinfo/pathogens/Dengue_virus_Info.

html.

72 Proc. Natl. Acad. Sci. Sect B. Biol. Sci. (January–March 2012) 82(1):69–80

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which has a high fatality rate. The rate of death from DHF

without DSS is usually quoted at 1–5%. This is believed to

be caused by immune enhancement when a person with

dengue antibodies due to a previous infection is subse-

quently infected by a DEN of a different serotype [1–4].

Pathogenesis

After an incubation period of 4–10 days, infection by any of

the four virus serotypes can produce a wide spectrum of

illness, although most infections are asymptomatic or sub

clinical. Primary infection is thought to induce lifelong

protective immunity against the infecting serotype [10].

Individuals suffering an infection are protected from clinical

illness with a different serotype within 2–3 months of the

primary infection but there is no long-term cross-protective

immunity [8]. The DEN enters via the skin while an infected

mosquito is taking a blood meal. During the acute phase of

illness the virus is present in the blood and its clearance from

this compartment generally coincides with defervescence.

Humoral and cellular immune responses are considered to

contribute to virus clearance by the generation of neutraliz-

ing antibodies and the activation of CD4? and CD8? T

lymphocytes. In addition, innate host defense may limit

infection by the virus. After infection, serotype specific and

cross-reactive antibodies and CD4? and CD8? T cells

remain measurable for years. Plasma leakage, haemocon-

centration and abnormalities in homeostasis characterize

severe dengue. The mechanisms leading to severe illness are

not well defined. Individual risk factors determine the

severity of disease and include secondary infection, age,

ethnicity and possibly chronic diseases (bronchial asthma,

sickle cell anaemia and diabetes mellitus) [8].

Seroepidemiological studies in Cuba and Thailand con-

sistently support the role of secondary heterotypic infection

as a risk factor for severe dengue, although there are a few

reports of severe cases associated with primary infection

[10–14]. Antibody-dependent enhancement of infection has

been hypothesized [15, 16] as a mechanism to explain severe

dengue in the course of a secondary infection and in infants

with primary infections. In this model, non-neutralizing,

cross-reactive antibodies raised during a primary infection,

or acquired passively at birth, bind to epitopes on the surface

of a heterologous infecting virus and facilitate virus entry

into Fc-receptor-bearing cells. The increased number of

infected cells is predicted to result in a higher viral burden

and induction of a robust host immune response that includes

inflammatory cytokines and mediators, some of which may

contribute to capillary leakage [17–19]. During a secondary

infection, cross-reactive memory T cells are also rapidly

activated; these proliferate, express cytokines and die by

apoptosis in a manner that generally correlates with overall

disease severity [20, 21]. Host genetic determinants might

influence the clinical outcome of infection [22], though most

studies have been unable to adequately address this issue.

Laboratory evidence requires one of the following:

• Isolation of DEN from clinical material

• Detection of dengue viral RNA in clinical material

• Detection of antibodies against dengue NS1 protein

• Detection of DEN specific IgM in the serum

• A significant rise in the level of DEN specific IgG

Preventive Measures

Vaccines

The first dengue vaccine was prepared in 1945 and still no

effective vaccine is available that indicates problems in its

development. An effective dengue vaccine is a distinct

possibility because the virus causes an acute infection and

the viraemia is removed within 5 days; immunity to infec-

tion with homologous DV serotype is long lasting; and

passive transfer of virus specific antibodies are protective

against subsequent challenge with that specific viral subtype

in animal models. The major obstacles in the development of

an effective dengue vaccine are incomplete understanding

of the pathogenesis of DHF; absence of an animal model of

DHF; and pre-existing heterotypic dengue antibodies, which

are a risk factor for DHF. An effective vaccine will have to be

Table 2 Reservoirs/vectors/modes of transmission reservoirs and modes of transmission for selected hemorrhagic fever viruses found in India

Agent Reservoir Arthropod vector Modes of transmission

Dengue Humans Aedes aegypti Bite of infected mosquito

KFD virus Rodents, bats, and other small mammals;

monkeys (e. g., black-faced langur,

South Indian bonnet macaque) appear

to be amplifying hosts

Ixodid Ticks (Haemaphysalisspinigera)

Bite of infected tick

Airborne through virus-containing

aerosols in laboratory setting

Hanta virus Murid Rodents with horizontal rodent

to rodent transmission

Absent Airborne transmission from

aerosol generated from

contaminated urine, feces and

saliva of infected rodent.

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Table 3 Differential diagnosis for viral hemorrhagic fever

Condition Agent(s) Distinguishing features

Bacterial and Rickettsial infections

Septicemia caused by

gram-negative

bacteria

Various Underlying illness is usually present

Staphylococcal or

streptococcal toxic

shock syndrome

Staphylococcus aureus Streptococcal TSS may be associated with necrotizing fasciitis.

Streptococcus pyogenes Staphylococcal TSS is often associated with characteristic epidemiologic

features (e.g., tampon use in menstruating women, antecedent trauma).

Meningococcemia Neisseria meningitidis Rapid progression to shock and often death may occur.

Secondary syphilis Treponema pallidum Maculopapular rash that begins on the trunk (palms and soles often

involved) is characteristic.

Constitutional symptoms often occur but are not as severe as would be

expected with VHF.

Septicemic plague Yersinia pestis Often occurs secondary to bubonic plague (characteristic bubo present in

groin, axilla, or cervical region).

Typhoid fever Salmonella typhi Symptoms of enterocolitis and abdominal pain may be more prominent

with typhoid fever than with VHF.

Hemorrhagic manifestations are generally less common than with VHF.

Rocky mountain

spotted fever

Rickettsia rickettsii A history of tick exposure may be obtained.

The disease occurs in April through May.

Most US cases occur in southeastern and south-central states.

Ehrlichiosis Ehrlichia chaffeensis A history of tick exposure history may be obtained.

Erhlichia phagocytophilia Petechial rash is uncommon.

Peripheral blood smear may show morulae in neutrophils of patients with

human granulocytic ehrlichiosis.

Leptospirosis Leptospira interrogans This is most often self-limited but may be severe in about 10% of

patients.

The disease is often associated with aseptic meningitis (characteristic of

the immune phase of illness).

Viral infections

Influenza Influenza virus Respiratory symptoms are prominent.

It is not associated with bleeding diathesis or rash.

It is usually seasonal (October to March in United States) or associated

with a history of recent cruise ship travel or travel to tropics.

Measles Rubeola virus Presenting features usually include cough, coryza, conjunctivitis.

Hemorrhagic features are rare.

Rubella Rubella virus Occurs in persons without history of rubella vaccination (such as migrant

workers).

Hemorrhagic features are extremely rare.

Hemorrhagic varicella Varicella-zoster virus Usually occurs in immunocompromised children.

Viral hepatitis Usually hepatitis A, B, C viruses

(hepatitis E and G virus and

other viruses also may cause)

Hepatic findings predominate.

Hemorrhagic manifestations are associated with fulminant hepatic failure.

It is most likely to mimic yellow fever or Rift Valley fever (both

characterized by icteric disease).

Parasitic infections

Malaria Plasmodium species Fever is cyclic (every 48 h for P vivax or P ovale; every 72 h for Pmalariae) or continuous with intermittent spikes (most common pattern

for P falciparum).

Hemolysis commonly occurs; hemorrhagic manifestations are less

common.

Parasites may be seen on microscopic examination of thick or thin

smears.

74 Proc. Natl. Acad. Sci. Sect B. Biol. Sci. (January–March 2012) 82(1):69–80

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tetravalent and should induce immunity to all four DV ser-

otypes simultaneously. Selection of the most promising DV

vaccine candidates rely mostly on comparing vaccine-

induced immune responses to a profile of protective immu-

nity developed from natural DV infections [23].

The dengue vaccine research focuses on the use of live

attenuated or inactivated vaccines, infectious clone-derived

vaccines, immunogens vectored by various recombinant

systems, subunit immunogens, and nucleic acid vaccines.

Serial passages of dengue viruses in PDK cells were used to

develop live attenuated vaccine. Initially, monovalent

vaccines were prepared using each of the DEN serotypes

followed by di-, tri- and tetra-valent vaccines that were

immunogenic and well tolerated by human subjects. A

chimeric YF-dengue type 2 virus vaccine was prepared,

using a recombinant cDNA infectious clone of a Yellow

fever vaccine strain (YF17D) as a backbone, into which the

PrM and envelope E genes of DEN were inserted. This

vaccine induced neutralizing antibodies in monkeys and

protected them against challenge with a wild type of DEN.

The safety as well as protective efficacy of the recombinant

DV tetravalent vaccine has been demonstrated in a monkey

challenge model. A candidate DNA vaccine expressing DEN

PrM and E proteins was developed and used for the immu-

nization of monkeys. This vaccine induces virus-neutraliz-

ing antibodies and gave partial protection against challenge

with homologous DEN. DEN grown in Vero cells was used

for the immunization of laboratory animals after inactiva-

tion, purification and concentration. The vaccine induces the

production of protective level of antibodies in monkeys.

Recombinant DNA techniques have provided the possibility

of cloning specific genes encoding protective antigens and

expressing them in other host cells, including E. coli, yeast

and insect cell systems [24].16

The question of whether any of the candidate dengue

fever vaccines will be ready by 2012 still is an open

question, although it is the declared objective of both GSK

and Sanofi Pasteur, both of which have presented timelines

compatible with licensure by 2012.17

Public Health Measures

Dengue infection can be prevented by:

• Mosquito control measures

• Personal protection measures such as long sleeves and

mosquito repellents

• Avoidance of mosquito-prone areas.

Control of Case

Isolate the patient and prevent mosquito access until fever

subsides.

Investigate the source of infection.

Control of environment

• Search for and eliminate breeding sites of Aedes ae-

gypti in the urban area.

Table 3 continued

Condition Agent(s) Distinguishing features

Acute conditions that may be associated with a bleeding diathesis

Hemolytic uremic

syndrome

Usually occurs as complication of

infection with Escherichia coliO157:H7 or other Shiga toxin-

producing E. coli

Disease involves a triad of renal involvement, thrombocytopenia, and

hemolytic anemia.

It is more common in young children.

Antecedent diarrheal illness occurs.

Hemorrhagic manifestations are uncommon, although bloody diarrhea

often occurs

Thrombotic

thrombocytopenic

purpura

May occur as complication of

infection with E. coli O157:H7

or other Shiga toxin–producing

E. coli, although may be

noninfectious

Disease includes renal involvement, thrombocytopenia, hemolytic

anemia, neurologic involvement

Hemorrhagic manifestations are uncommon

Idiopathic

thrombocytopenic

purpura

Noninfectious Low platelet count is predominant feature

Disease is generally not accompanied by severe systemic toxicity

Acute leukemia Noninfectious Peripheral blood smear shows characteristic features of leukemia.

Collagen vascular

disease

Noninfectious Acute onset of febrile illness not likely

TSS toxic shock syndrome

16 http://www.who.int/vaccine_research/diseases/vector/en/index1.html.17 http://www.who.int/vaccine_research/diseases/vector/en/index1.html.

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• Use mosquito repellents, mosquito nets and other

methods of personal protection.

• Control Aedes aegypti near airports.

• Prevent importation of new vectors, for example Aedes

albopictus.

Individual protective measures to avoid mosquito bites

during the day should include:

• Application of insect repellents (e.g. DEET-based repel-

lent, etc.) on exposed skin: the type and concentration of

repellents depend on age and presence of pregnancy;

• Wearing appropriate clothing (long sleeves and trousers);

• The use of a mosquito net (preferably insecticide-

treated), particularly recommended for children and

viraemic people.

Infected persons should avoid mosquito bites during the

first few days of illness to prevent further dissemination of

the virus.

Local Community Measures

The vector mosquitoes mainly colonize small water col-

lections, such as flower plates and pots, barrels, used tyres,

and sometimes tree-holes and rock pools. Therefore, the

removal of these breeding sites by emptying stagnant water

around the houses is the most efficient way to avoid

mosquito proliferation.

Key Areas of Uncertainty

Key areas of uncertainty include: the lack of vaccines and

antiviral drugs, the resistance of the vector mosquitoes to

insecticides, the role and impact of social mobilisation for

control of mosquitoes, the expansion of the geographic

distribution of potential Aedes vectors, the importance of

increasing international travel, and virus circulation

worldwide [25, 26].

Kyasanur Forest Disease Virus

In 1957, several dead monkeys were noticed in the

Kyasanur forest in Shimoga district in Karnataka along

with a severe prostrating illness in some of the villagers in

the area. A similar illness has been observed in the locality

a year earlier also. A new arbovirus, antigenically, related

to the Russian spring-summer encephalitis complex of

viruses was isolated by investigators from the Virus

Research Centre, (now the National Institute of Virology)

Poona, from patients and dead monkeys. It was named the

Kyasanur forest disease (KFD) virus after the name of the

place from where the first isolations were made [3, 27, 28].

KFD a tick-borne infection, is relatively rare and found

only in one region in the southwestern part of India. KFD

virus was first recognized in 1957 when it was isolated

from a sick monkey from the Kyasanur forest in Karnataka

State, India. Rodents, monkeys, bats, and other small

mammals are the natural reservoirs. Larger animals (such

as goats, cows, and sheep) may become infected, but they

don’t have a role in transmission of the disease. Natural

infections have been identified only in several districts

of Karnataka State. Outbreaks occur periodically and are

usually signaled by epizootics in the local monkey

population [29].

Continuing deaths in monkeys and an average of

400–500 human cases have been seen annually over the

past 5 decades, commonly occurring in evergreen, semi-

evergreen, and neighboring, moist, deciduous forest areas.

An array of tick species, mainly Haemaphysalis spinigera,

acts as vector for KFDV. This species of tick is widely

Fig. 5 Enzootic transmission

cycle

Fig. 6 Life cycle of dengue [10]. Extrinsic incubation period:

incubation occurring in the vector i.e. mosquito. Intrinsic incubation

period: incubation occurring in human

76 Proc. Natl. Acad. Sci. Sect B. Biol. Sci. (January–March 2012) 82(1):69–80

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distributed in tropical evergreen and deciduous forests of

southern and central India and Sri Lanka. KFDV has also

been isolated from 7 other species of this genus and from

Dermacentor and Ixodes ticks. This disease is transmitted

by ticks among ground birds and small mammals such as

the white-tailed rat, white-bellied rat, shrew, and bat. High

titers of virus can be obtained after experimental infection

of black-napped hares, porcupines, flying squirrels,

Malabar giant squirrels, three-striped squirrels, gerbils,

mice, long-tailed tree mice, and shrews [30].

A seasonal pattern has been noted, with most of the

cases occurring in the spring months. Outbreaks of the

disease have occurred in the area periodically since it was

first identified, but it has spread only for a few kilometers

from the original site in all these years. Human cases were

also found among persons who visited forests to collect

firewood, grass, and other forest products.

KFD has an incubation period of about 3–8 days,

manifests with sudden onset of fever with chills, headache,

conjunctivitis, myalgia and severe prostration. The disease

duration is of about 5–12 days. Some cases develop hem-

orrhages into the skin, mucosa and viscera. The major

clinical manifestations are VHF or meningo encephalitis

and case fatality rate is [30% [27–30]. The National

Institute of Virology has produced an effective killed

vaccine against KFD.

Hantaviruses

Hantaviruses causes VHF with renal syndrome (HFRS) and

hantavirus cardiopulmonary syndrome (HCPS). These are

emerging as a global cause of concern and are increasingly

being reported from India. The first Hantavirus to be cul-

tured was Thottapalayam virus from Vellore in 1964.

Serological investigation of patients with pyrexic illness

reveals anti-hantavirus IgM in about 14.7% cases. Sero-

positivity of Hantavirus in the general population is 4%

while it is much higher in persons coming in contact with

the rodents. Since there is no arthropod vector, there is

slow movement of Hantavirus species with natural rodent

to rodent transmission, which is also a rate limiting factor

to wide spreading of the infection [31, 32].

Clinical picture and severity of HFRS and HCPS

depends on the infecting species.

HFRS

The incubation period is of 1–5 weeks and the onset of

diseases is with fever and influenza like symptoms.

Hemorrhagic manifestations, if seen, are in the form of

flushing of face, infection of the conjunctiva and mucus

membranes. The disease is described in five phases:

(1) Febrile phase lasting for 3–5 days: This is character-

ized by development of acute influenza like illness,

nausea, vomiting, back and abdominal pain. Protein-

uria develops on the 4th day. During the end of this

phase flushing of the face and conjunctival suffusion

is seen.

(2) Hypotensive (shock) phase lasting for a few hours to a

few days: This is associated with thrombocytopenia

and in one-third of cases death may occur. Proteinuria

tends to persist.

(3) Oliguric phase lasting for 3–5 days: There are signs

of acute renal failure and about half the deaths occur

during this time.

(4) Diuretic phase: It occurs in those who have survived

the earlier phases and lasts from a few days to a few

weeks with progressive improvement of renal

functions.

(5) Convalescent phase: There is sudden arrest of plasma

leak with concomitant reabsorption of extravagated

plasma and fluids.

Three kinds of clinical presentations of Hantavirus

infections can occur, namely, fever with shock and multi

organ failure, fever with oliguric acute renal failure and

febrile illness without any renal failure. Thus it has to be

differentiated from influenza, viral hepatitis, streptococcal

pharyngitis, leptospirosis, dengue fever and scrub typhus.

HCPS

It occurs mostly in adults with a case fatality rate of 33%.

There is a prodromal phase with fever, headache, chills and

myalgia and can be confused with other viral infections.

The prodrome is followed by the onset of cardiopulmonary

phase with pulmonary oedema, dyspnoea and hypoxemia.

Patients with fatal illness progress to depression, respira-

tory failure and acidosis leading to fatal arrhythmias.

Common laboratory findings are presence of hemocon-

centration, thrombocytopenia and atypical lymphocytes.

HFRS and HCPS are uncommon in children [27].

Treatment and Prevention

While there are no effective antiviral drugs for the treat-

ment of Hantavirus infections, trials of ribavarin done in

China have reported reduction in case fatality rates of

HFRS. Ribavarin, however, is ineffective in the treatment

of HPS. Prevention of exposure to rodents is the best way

to avoid infection. Rodents should be avoided in human

dwellings and proper food storage practices must be

employed. Rodents as pets should be discouraged. There

are a few inactivated vaccines (Hantvax) licensed for use in

Korea but protection is short lived. Baculovirus and

Proc. Natl. Acad. Sci. Sect B. Biol. Sci. (January–March 2012) 82(1):69–80 77

123

vaccinia-expressed Hantavirus glycoproteins confer protect

in animal models. There is ongoing research on nucleic

acid vaccines against Hantavirus [33].

Differential Diagnosis

A wide range of conditions (bacterial, viral, and parasitic

infections as well as noninfectious causes) should be con-

sidered in the differential diagnosis of VHF [34]. However,

most of these conditions do not cause bleeding manifes-

tations as a primary feature and most are not likely to occur

epidemiologically as a point-source epidemic with simul-

taneous presentation of many cases. Primary agents to

consider in the differential diagnosis are outlined in the

Table 3 [24, 31].

When to Consider the Diagnosis of VHF

Most clinicians have little or no clinical experience with

the syndromes that characterize VHF; therefore, a high

index of suspicion is needed to make an accurate diagnosis.

The diagnosis of VHF should be considered for any

patient who presents with:

• Acute onset of fever (less than 3 weeks’ duration)

• Severe prostrating or life-threatening illness

• Bleeding manifestations (i.e., at least two of the

following: hemorrhagic or purpuric rash, petechiae

[particularly in nondependent areas], epistaxis, hema-

temesis, hemoptysis, blood in stool, or other evidence

of bleeding)

• No predisposing factors for a bleeding diathesis

In naturally occurring cases, an appropriate travel or

exposure history will usually be present.

Tests for Detection of Hemorrhagic Fever Virus

Infection (Available Only at Specialized Laboratories)

• Antigen detection by antigen-capture enzyme-linked

immunosorbent assay (ELISA), performed on serum or

other samples, can be used to detect most hemorrhagic

fever viruses [35–38].

• Serology (either testing an acute-phase specimen for

IgM antibody or testing paired sera) also can be used to

diagnose most VHF infections.

• Reverse transcriptase (RT)-PCR methods have been

developed for a number of hemorrhagic fever viruses

[34, 37, 39–46]. As with other rare diseases, the

positive predictive value of PCR in the absence of other

corroborating medical or epidemiologic evidence is

exceedingly low.

• Cell culture: Although this is the ‘‘gold standard’’ of

virus detection and identification, performance of cell

culture with these viruses is time consuming and

extremely dangerous, and should be performed on

suspect cases only at BSL-4 laboratories.

• Generally, hemorrhagic fever viruses can be recovered

from serum or virtually any infected tissue.

• Most hemorrhagic fever viruses will grow in Vero

and other mammalian cell lines. Passage in labora-

tory animals may increase cell culture sensitivity

[29].

Treatment

Supportive care is essential for patients with all types of

VHF and includes the following:

• Maintenance of fluid and electrolyte balance, with

hemodynamic monitoring as needed

• Mechanical ventilation, as indicated

• Dialysis, as indicated

• Steroids have not been shown to be of value; however,

because adrenal involvement may occur in VHF cases,

steroids could be considered in certain situations [47,

48].

• Anticoagulant therapies, aspirin, nonsteroidal anti-

inflammatory medications, and intramuscular injections

are contraindicated

• Appropriate therapy for secondary infections

Management of severe bleeding complications is con-

troversial. Potential therapies include

• Clotting factor concentrates

• Platelets

• Fresh frozen plasma

• Heparin for DIC

Conclusion

VHFs are important cause of morbidity and mortality in

children as well as in adults globally. Since most of VHF

are arthropod vector borne disease, with the exception of

Hanta VHF, therefore public health strategies for elimi-

nation of vector as well as such protective measures by

individuals will act synergistically to reduce incidence of

VHF. Currently there are no specific antiviral agents and

management strategy of VHF is largely symptomatic.

Further research is being done to identify efficient treat-

ment and management strategy which include use of

effective vaccines, especially against Dengue fever, since

humans are the only reservoirs. In countries like India

where VHF is endemic professionals as well as commu-

nity must be aware of its symptoms and management.

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123

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