Dengue Guideline PDF

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Dengue Guideline pdf

Dengue Guideline


Dengue is a self limiting acute mosquito transmitted disease characterized by fever, headache, muscle, joint pains, rash, nausea and vomiting. Dengue Fever (DF) is caused by an arbovirus and spread by Aedes mosquitoes.

Some infections result in Dengue Haemorrhagic Fever (DHF) and in its severe form Dengue Shock Syndrome (DSS) can threaten the patientís life primarily through increased vascular permeability and shock.

Over the past two decades, there has been global increase in the frequency of DF, DHF and its epidemics, with a concomitant increase in disease incidence.

Various factors responsible for the resurgence of dengue epidemic are:

(i) un-precedented human population growth;

(ii) un-planned and un-controlled urbanization;

(iii) inadequate waste management;

(iv) water supply mismanagement;

(v) increased distribution and densities of vector mosquitoes;

(vi)lack of effective mosquito control has increased movement & spread of dengue viruses and development of hyper endemicity and

(vii) deterioration in public health infrastructure.

Dengue in India

The first evidence of occurrence of DF in the country was reported during 1956 from Vellore district in Tamil Nadu.

The first DHF outbreak occurred in Calcutta (West Bengal) in 1963 with 30% of cases showing haemorrhagic manifestations. All the four serotypes i.e. Dengue 1,2,3 and 4 have been isolated in India.

As Ae aegypti breeding is more common in urban areas the disease was observed mostly prevalent in urban areas.

However, the trend is now changing due to socio economic and man made ecological changes, It has resulted in invasion of Ae.

aegypti mosquitoes into the rural areas, which has tremendously increased the chances of spread of the disease to rural areas.

Recurring outbreaks of DF/DHF have been reported from various States/UTs namely Andhra Pradesh, Delhi, Goa, Haryana, Gujarat, Karnataka, Kerala, Maharashtra, Rajasthan, Uttar Pradesh, Pondicherry, Punjab, Tamil Nadu, West Bengal and Chandigarh.

Epidemiology Dengue is one of the most important emerging viral disease of humans in the world afflicting humanity in terms of morbidity and mortality. Currently the disease is endemic in all continents except Europe.

The Epidemiology of dengue is a complex phenomenon that mainly depends upon an intricate relationship between the 3 epidemiological factors: the host (man and mosquito), the agent (virus) and the environment (abiotic and biotic factors).

The complexity of relationship among these factors eventually determines the level of endemicity in an area. 2.2 Agent Factor The dengue viruses are the members of the genus flavivirus. These small (50nm) viruses contain single stranded RNA.

There are four virus serotypes, which are designated as DEN-1, DEN-2, DEN-3 and DEN-4.

Although all four serotypes are antigenicaly similar, they are different enough to elicit cross-protection only for a few months after infection by any one of them.

Infection with any one serotype confers lifelong immunity to the virus serotype.

Man and mosquito are reservoirs of infection. Transovarian transmission (infection carried over to next progeny of mosquitoes through eggs) has made the control more complicated.

Vector Dengue viruses are transmitted by the bite of female Aedes (Ae) mosquitoes. Ae.

aegypti is the most potential vector (Fig.3) but other species such as Ae albopictus, Ae. polynesiensis and Ae. niveus have also been incriminated as secondary vectors. In India Ae.

aegypti is the main vector in most urban areas; however, Ae albopictus is also found as vector in few areas of southern India.

FemaleAedes mosquito deposits eggs singly on damp surfaces just above the water line.

Under optimal conditions the life cycle of aquatic stage of Ae. aegypti (the time taken from hatching to adult emergence) can be as short as seven days.

The eggs can survive one year without water.At low temperature, however, it may take several weeks to emerge.

Ae. aegypti has an average adult survival of fifteen days. During the rainy season, when survival is longer, the risk of virus transmission is greater. It is a day time feeder and can fly up to a limited distance of 400 meters.

To get one full blood mea the mosquito has to feed on several persons, infecting all of them.

4 Environmental Factors The population of Ae. aegypti fluctuates with rainfall and water storage.

Its life span is influenced by temperature and humidity, survives best between 16º-30º C and a relative humidity of 60-80%. Ae.

aegypti breeds in the containers, in and around the houses.

Altitude is an important factor in limiting the distribution of Ae. aegypti, it is distributed between sea level and 1000 ft above sea level. Ae. aegypti is highly anthropophilic and rests in cool shady places.

The rural spread of Ae. aegypti is a relatively recent occurrence associated with the development of rural water supply schemes, improved transport systems, scarcity of water and like style changes. Ae.

aegypti breeds almost entirely in domestic man-made water receptacles found in and around households, construction sites and factories; natural larval habitats are tree holes, leaf axils and coconut shells.

In hot and dry regions, overhead tanks and ground water storage tanks become primary habitats.

Unused tyres, flower pots and desert coolers are among the most common domestic breeding sites of Ae.

Aegypti Host Factor Dengue virus infects humans and several species of lower primates but in India man is the only natural reservoir of infection.

All ages and both sexes are susceptible to dengue fever. Secondary dengue infection is a risk factor for DHF including passively acquired antibodies in infants.

Travel to dengue endemic area is an important risk factor, if the patient develops fever more than 2 weeks after travel, dengue is unlikely.

Migration of patient during viremia to a non endemic area may introduce it into the area. 2.6 Transmission cycle The female Ae. aegypti usually becomes infected with dengue virus when it takes blood meal from a person during the acute febrile (viraemia) phase of dengue illness.

After an extrinsic incubation period of 8 to 10 days, the mosquito becomes infected and virus is transmitted when the infective mosquito bites and injects the saliva into the wound of the person (Fig 5).

There is evidence that vertical transmission of dengue virus from infected female mosquitoes to the next generation occurs through eggs, wihch is known as transovarian transmission.

Language English
No. of Pages39
PDF Size2 MB

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