arboviral epidemiology

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Dengue : :

Dengue :

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Dengue Virus:

Dengue Virus Causes dengue and dengue hemorrhagic fever Is an arbovirus Composed of single-stranded RNA Has 4 serotypes (DEN-1, 2, 3, 4) Transmitted by mosquitoes

Dengue Viruses:

Dengue Viruses Each serotype provides specific lifetime immunity, and short-term cross-immunity All serotypes can cause severe and fatal disease Genetic variation within serotypes Some genetic variants within each serotype appear to be more virulent or have greater epidemic potential

II. Vector:

II. Vector

Aedes aegypti Mosquito:

Aedes aegypti Mosquito

Aedes aegypti:

Aedes aegypti Dengue transmitted by infected female mosquito Primarily a daytime feeder Lives in and around human habitation Lays eggs and produces larvae preferentially in artificial containers

Aedes aegypti Breeding Sites:

Aedes aegypti Breeding Sites


Life Cycle Of Aedes Aegypti 2 – 3 Days 4-5 Days 1-2 Days Eggs Larvae Pupae Stagnant water

Biting habits:

Biting habits Only the female mosquito bites Bites mainly in day time Bites humans and animal Powerful bites / fearless bites Bites 3 to 4 times for a satisfactory meal

Resting habits Flying habits :

Resting habits Flying habits Rests in dark corners, walls, umbrellas, book shelves, coolers, bed covers. Flies around 100 mts from breeding places This factor helps in its eradication Transported to long distances by aero planes , ship, train.

Transmission of Dengue Virus by Aedes aegypti:

Transmission of Dengue Virus by Aedes aegypti Viremia Viremia Extrinsic incubation period Days 0 5 8 12 16 20 24 28 Human #1 Human #2 Illness Mosquito feeds / acquires virus Mosquito refeeds / transmits virus Intrinsic incubation period Illness

Replication and Transmission of Dengue Virus (Part 1):

Replication and Transmission of Dengue Virus (Part 1) 1. Virus transmitted to human in mosquito saliva 2. Virus replicates in target organs 3. Virus infects white blood cells and lymphatic tissues 4. Virus released and circulates in blood 3 4 1 2

Replication and Transmission of Dengue Virus (Part 2):

Replication and Transmission of Dengue Virus (Part 2) 5. Second mosquito ingests virus with blood 6. Virus replicates in mosquito midgut and other organs, infects salivary glands 7. Virus replicates in salivary glands 6 7 5

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Manifestation Of Dengue Virus Infections ASYMPTOMATIC DSS SYMPTOMATIC Without haemorrhage With unusual haemorrhage No shock Undifferentiated Fever Dengue Fever Dengue Haemorrhagic Fever

2A) Clinical Characteristics of Dengue Fever:

2A) Clinical Characteristics of Dengue Fever Fever Headache Muscle and joint pain Nausea/vomiting Rash Hemorrhagic manifestations

Symptoms of Dengue Fever :

Symptoms of Dengue Fever

Unusual Presentations of Severe Dengue Fever:

Unusual Presentations of Severe Dengue Fever Encephalopathy Hepatic damage Cardiomyopathy Severe gastrointestinal hemorrhage

2B)Hemorrhagic Manifestations of Dengue:

2B)Hemorrhagic Manifestations of Dengue Skin hemorrhages: petechiae , purpura , ecchymoses Gingival bleeding Nasal bleeding Gastro-intestinal bleeding: hematemesis , melena , hematochezia Hematuria Increased menstrual flow

C1) Clinical Case Definition for Dengue Hemorrhagic Fever:

C1) Clinical Case Definition for Dengue Hemorrhagic Fever Fever, or recent history of acute fever Hemorrhagic manifestations Low platelet count (100,000/mm 3 or less) Objective evidence of “leaky capillaries:” elevated hematocrit (20% or more over baseline) low albumin pleural or other effusions 4 Necessary Criteria:



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23 DHF - petechiae

Tourniquet Test:

Tourniquet Test Inflate blood pressure cuff to a point midway between systolic and diastolic pressure for 5 minutes Positive test: 20 or more petechiae per 1 inch 2 (6.25 cm 2 )

Positive Tourniquet Test:

Positive Tourniquet Test

Four Grades of DHF:

Four Grades of DHF Grade 1 Fever and nonspecific constitutional symptoms Positive tourniquet test is only hemorrhagic manifestation Grade 2 Grade 1 manifestations + spontaneous bleeding Grade 3 Signs of circulatory failure (rapid/weak pulse, narrow pulse pressure, hypotension, cold/clammy skin) Grade 4 Profound shock (undetectable pulse and BP)

C2) Clinical Case Definition for Dengue Shock Syndrome:

C2) Clinical Case Definition for Dengue Shock Syndrome 4 criteria for DHF Evidence of circulatory failure manifested indirectly by all of the following: Rapid and weak pulse Narrow pulse pressure (  20 mm Hg) OR hypotension for age Cold, clammy skin and altered mental status Frank shock is direct evidence of circulatory failure

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Warning Signs for Dengue Shock When Patients Develop DSS: 3 to 6 days after onset of symptoms Initial Warning Signals: Disappearance of fever Drop in platelets Increase in hematocrit Alarm Signals: Severe abdominal pain Prolonged vomiting Abrupt change from fever to hypothermia Change in level of consciousness (irritability or somnolence) Four Criteria for DHF: Fever Hemorrhagic manifestations Excessive capillary permeability  100,000/mm 3 platelets

Clinical Evaluation in Dengue Fever:

Clinical Evaluation in Dengue Fever Blood pressure Evidence of bleeding in skin or other sites Hydration status Evidence of increased vascular permeability-- pleural effusions, ascites Tourniquet test

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AGENT Genus : Flavivirus fibricus , Group B Arbovirus Family : Toga virus The yellow fever virus is 35-40 nm in size. It consists of a single strand of RNA virus

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The photomicrograph shows multiple virions of the yellow fever virus at a magnification of 234,000x



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Aedes mosquitoes , including A. aegypti , A. africanus , A. simpsoni , and A. albopictus (Asian tiger mosquito ) Urban yellow fever is transmitted by the Aedes aegypti mosquito only. Jungle, or sylvatic , yellow fever is transmitted by Haemagogus and other mosquitoes (such as Masoni africana ) of the forest canopy (tree-hole breeding mosquitoes).

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Reservoir: Monkey, Human, Mosquito Incubation period: Intrinsic IP: 3to 6 Days Extrinsic IP: 1to 2 weeks Period of communicability: man: First 4 days of illness, mosquito: after extrinsic incubation period 8-14days Mode of Transmission : 1. Sylvan cycle 2. Urban cycle

Host Factors:

Host Factors

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Race: No known racial predilection exists. Sex: Both sexes are infected equally Age: All ages are susceptible to yellow fever. Jungle yellow fever primarily affects non immunized adults who work as foresters,wood cutters & hunters in endemic areas and persons residing on the edge of the jungle. Infants born of immune mothers have antibodies up to 6 months of life



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The natural host for the yellow fever virus in forest areas is non-human primates (usually monkeys and chimpanzees ). The vectors of yellow fever in forest areas in Africa are Aedes africanus . In South America, the primary vector is the Haemagogus species. In urban areas of both Africa and South America, the vector is Aedes aegypti .

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The natural yellow-fever cycle is mosquito-monkey-mosquito. The shift from jungle yellow fever to urban yellow fever is thought to be the result of humans entering the sylvan setting and becoming part of the yellow-fever cycle: Initially, wood cutters and other forest workers were bitten by forest-canopy mosquitoes carrying the yellow-fever virus.  The humans then returned to the urban settings.

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Clinical features of yellow fever · An acute phase lasting for four to five days and presenting with: - a sudden onset of fever - headache or backache - muscle pain - nausea - vomiting - red eyes ( injected conjunctiva). The diagnosis can be strongly suspected when Faget's sign is present. Faget's sign: The simultaneous occurrence of a high fever with a slowed heart rate.

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A toxic phase can follow the period of remission and presents with: - jaundice - dark urine - anuria - bleeding from the gums, nose or in the stool - hemoptysis - hiccups - diarrhoea - Bradycardia in relation to fever

Chikungunya :


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Group A Alphavirus Chikungunya virus Family : Toga virus It is believed that there are two distinct lineages of the Chikungunya virus, one containing Western African and the second comprising all Southern and East African strains. Isolated for the first time from a Tanzanian outbreak in 1952



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Mosquito born disease Aedes aegypti & aedes albopictus In some part of the world culex species are important Aedes albopictus

Epidemiology Chikungunya risk zones :

Epidemiology Chikungunya risk zones


Symptoms Typically debilitating poly- arthralgia Fever reaching 39°C Petechial or maculopapular rash on limbs and trunk Epitaxis , minor hemorrhage Self-limiting- usually last 5-7 days May become chronic in the elderly !!Not life-threatening!!

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