Posted by Dr. Bijoykumar Barik on Thursday, 22nd July 2010DENGUE FEVER
Dengue fever (DF) is an acute febrile viral infection presenting with intense headache, bone ache, rash, leucopenia. Dengue haemorrhagic fever (DHF) is associated with pneumonia and circulatory failure leading to Dengue Shock Syndrome (DSS). Currently it poses a threat to 2.5 billion people in over 100 tropical and subtropical areas of World. International travel, new serotype to susceptible populations are a threat. Proper epidemiological and laboratory surveillance is needed to further control, prevent and treat the cases.
Dengue is a Spanish phrase “Ke denga Pepo” meaning “Cramp like seizure caused by evil spirit” during Carribean out break in 1827-1828. Worldwide incidence is 100 million. In India outbreak occurred in 1993, 1996, 2003 and 2006. In recent outbreak there were 167 death out of which at Delhi there was 61.
Belongs to family Flaviviridae (Genus – Flavivirus, species – Dengue) having 4 sero subtypes (DEN-1,2,3,4) distinguished by serological method. The virus has a single standard RNA genome surrounded by icosahedral nucleocapsid and covered by lipid envelope. The virion is about 50nm diameter. The genome is about 11 kilobases in length, the genome sequence of all 4 types are known. The genome is composed of 3 protein genes core (C), membrane associated (M) and envelope (E) and seven nonstructural protein genes. Infection by one serotype produces lifelong immunity against same serotype by partial or temporary immunity against other serotypes.
The mosquito Ae aegypti found around the globe in tropical and subtropical region usually between latitude 350N and 350S and altitude of 100meters. The mosquitoes invade in warm season and die in winter. Because of its high anthropophilic nature and close proximity to human and indoor efficient vector for arbovirus. Its eggs can withstand long period of desiccation even more than a year.
Other Aedes mosquitoes for dengue are Ae albopictus, Ae polynesiensis, several species of Ae scutillaris complex.
The mosquito is known as Tiger mosquito as it has white strips on black body. It is a fearless biter. The biting hour is 2 hour after sunrise and few hours before sunset. It can fly upto 10 meters. The mosquito breads on artificial accumulation of water like discarded tin, flower pot, cocoanut shell, earthen pots, cooler water etc.,
All 4 serotypes infect human. At different settings DEN-2, DEN-3 and DEN-4 has been responsible for epidemics. The acute phase of infection following an incubation of 3-14 days lasts about 5-7 days and followed by immune response. Usually high viraemia in human leads to greater percentage of infection to feeding mosquitoes.
. The commonest age group is below 12 years.
. Females suffer more than male
. Race – Caucasian> Black
. Nutritional status – Poor nutritional status is protective.
Once infected the Ae aegypti mosquito remain infected lifelong and transmit to human during probing and feeding. Infected female mosquito transmits to next generation by transovarian transmission. Though human is the commonest amplifying host, monkeys at some places may be the host. The virus circulates during fever and viraemia. The virus develops in the biting mosquito for 8-10 days before infecting a healthy human. This extrinsic incubation period depends on environmental factors.
PATHOGENESIS OF DHF/DSS
The two main pathophysiological changes in DHF/DSS are:
. Increased vascular permeability giving rise to plasma loss, haemoconcentration, low pulse pressure and signs of shock.
. Disorder of haemostasis involving vascular changes, thrombocytopenia coagulopathy.
Activation of complement system with decrease of C3 and C5 levels are seen. Mediators of vascular permeability and bleeding phenomena are not clear. Platelet defects are quantitative and qualitative. There is enhanced viral replication in macrophages by heterotype antibodies. The secondary infection by a different serotype , cross reactive antibodies may increase the number of infected monocytes as dengue virus antibody complexes are taken into these cells. This results in increase of CD4+ and CD8+ cytotoxic antibodies. Activation of T cells releases cytokines rapidly. Lysis of infected monocytes mediated by cytotoxic lymphocytes result in plsma leakage and haemorrhage.
Sequence of infection:
. Serotype 1 Serotype 2 more dangerous
. Serotype 4 Serotype 3 Less dangerous
. Serotype 2 Most dangerous.
PATHOLOGY OF DHF
In autopsy it has been found in order of incidence - skin and S.C. tissues, G.I mucosa, heart , liver. Subarchnoid and cerebral haemorrhage are rare.
Serous effusion (exudative) seen in pleura, peritoneum, rarely in pericardium. The capillaries and venules of involved organs show perivascular bleeding , monocyte and lymphocyte infiltration, intravascular clot.
In liver there occurs focal necrosis of hepatic cells , swelling , councilman bodies hyaline necrosis of Kupffer cells. Mononuclear proliferation occurs commonly in sinusoids and rarely in portal areas.
In autopsy viral antigen commonly seen in liver, spleen, thymus, lymphnode, lung cells. Virus has been isolated from bone marrow, brain, heart, kidney, liver, lung, lymphnode, GIT.
In nonfatal DHF the bone marrow shows depression of all haemopoitic cells which improve after fever subsides. Kidney shows mild immune complex type glomerulonephuits which resolve after 3 weeks without any residue. Biopsy of skin rash shows perivascular oedema of the terminal microvasculature of dermal papillae with infiltration of lymphocytes and monocytes. Phagocytes bearing antigen have been found in this area. Deposition of serum complement, immunoglobulin and fibrinogen on vessels has been detected.
Dengue infection may present as asymptomatic, undifferentiated fever, DF, DHF and DSS.
I. Dengue fever:
. The clinical features depends on age. Infants and young children have febrile illness with maculopapular rashes.
. Older children and adult may have mild febrile syndrome or classical disease by high fever of abrupt onset sometimes with 2 peaks (sadodle backed) severe headache, pain behind eyes, muscle, bone , joint pain (break bone fever), nausea, vomiting, rash. Petechial skin lesions are common. Leucopenia and thrombocytopenia is common. Recovery is associated with fatigue and depression. In some epidemics may have bleeding complications like epistaxis, gum bleeding, GI bleeding , haematuria, monorrhagia.
. The case fatality is < 1%.
. Haemorrhage in DF is to be differentiated from DHF where there is haemoconcentration.
. DF is to be differentiated from Chikungunya fever a similar vector borne viral disease with similar epidemiology and overlapping distribution.
II. Dengue Haemorrhagic fever (DHF)
. The 4 typical manifestations are high fever, haemorrhagic phenomena, hepatomegaly and circulatory failure.
. Moderate to marked thrombocytopenia with haemoconcentration distinguish it form DF. So also plasma leakage giving rise to serous effusion and hypoproteinemia.
. Commonly sudden high fever accompanied by facial flush and various nonspecific symptoms and signs may occur like anorexia, nausea, vomiting, constipation, diarrhoea, abdominal pain, infected pharynx, rhinitis , maculopapular rash, myalgia, arthralgia, enanthema, abnormal reflex, palpable spleen, febrile convulsion (children) coma.
. Common haemorrhagic phenomenon is a positive tourniquet test, easy brushing and bleeding from venepuncture site. Discrete fine petechiae over extremities, axillae, face , soft palate are seen during febrile period. Epistaxis, gingival bleeding are infrequent and GI bleeding may occur during fever.
. Liver is palpable in early febrile phase and varies in size but does not correlate with severity though hepatomegaly is more in shock syndrome. Liver is tender without jaundice. Splenomegaly is common in infants.
. The course – In severe cases after 2-7 days of fever, rapid fall of temperature, circulatory disturbances. In less severe cases mild symptoms reflect less plasma leakage. Many patients recover spontaneously after fluid and electrolyte correction. In severe cases patient may go to shock and death.
. DHF can be graded as per severity of symptoms and signs
Grade – I: Fever , nonspecific constitutional symptoms. Only haemorrhagic sign is +ve , Tourniquet test and /or easy brushing.
Grade – II: Grade I symptoms with spontaneous bleeding manifestation of skin and other sites.
Grade – III: Circulatory failure in form of rapid, thready pulse , hypotension, cold , clammy skin and restlessness.
Grade – IV: Profound shock with undetectable pulse and BP.
. During convalescence from DHF sinus bradycardia, arrythmia, confluent petechial rash with small round normal skin are seen. Maculopapular rash are less common in DHF than DF. The course of DHF is usually 7-10 days.
III. Dengue shock syndrome (DSS)
Sudden deterioration of patient after 2-7 days of febrile illness when sudden fall of temperature with signs of circulatory failure like cold, clammy skin, circumoral cyanosis, rapid, thready pulse and low pulse pressure, hypotension. Initially lethargic later may be restless. Acute abdominal pain may proceed shock. If not timely treated patient passes to profound shock stage with imperceptible BP and pulse. But consciousness is intact throughout. The duration of shock is short. The patient dies within 12 – 24 hours or recovers following volume replacement. Pleural effusion and ascites may be detected clinically or radiologically.
Uncorrected shock can give rise to complications like metabolic acidosis, severe bleeding from GIT and other organs with poor prognosis. Convulsion may occur in intracranial haemorrhage and may be comatose. Encephalopathy may occur due to metabolic, electrolyte disturbance and intracranial bleeding.
Convalescence in corrected DSS is short and uneventful. Reviving from shock patient recovers within 2-3 days with adequate urination and appetite. Ascites and pleural effusion may recover later.
COMPLICATION AND UNUSUAL MANIFESTATIONS
The unusual manifestations like CNS involvement giving rise to convulsion, spasticity, altered sensorium , transient paresis. Febrile convulsion may occur in children. Encephalopathy may be due to hypotonic solution replacement or DIC. Intracranial bleeding and brainstem herniation due to cerebral edema may occur.
Some iatrogenic complications like sepsis, pneumonia, wound infection and overhydration may occur.
Liver failure may occur in serotype1, 2, 3 with both primary and secondary infection. Hepatic necrosis with detectable dengue antigen in hepatocytes. The cause of liver damage is not known. Renal failure is a terminal event.
Other unusual manifestations are acute renal failure, haemolytic uraemic syndrome (in cases of haemoglobinopathy and G6PD deficiency). Simultaneous infections like leptospirosis , Hepatitis B, typhoid fever, chicken pox, melioidosis contribute to unusual manifestations.
1. Thrombocytopenia and haemoconcentration is a constant finding of DHF.
A. Platelet count < 100000/mm3 found between 3-8th day, often along with or before changes in Haematocrit.
B. A rise in Haematocrit is always present more so in shock. A rise of 20% or more is definite evidence of increased vascular permeability and plasma leakage.
C. A relation of drop in platelet and rise in Haematocrit is unique of DHF and occur before defervescence and onset of shock.
D. The WBC count is variable at onset ranging from leucopenia to mild leucocytosis but leucopenia with fall of neutrophil is common at the end of febrile illness. Ralative lymphocytosis with atypical lymphocytes is common before shock.
E. A transient mild albuminuria with +ve occult blood in stool is seen.
F. Coagulation profiles may show reduced fibrinogen, prothrombin, factor VIII, IX and antithrombobin III.
G. Reduced antiplasmin seen in some cases, serum albumin reduced.
H. In severe liver dysfunction reduced level of Vit K dependent factors like factor V, VII, IX, X are seen. Prothrombin time and partial thromboplstin time is prolonged in 30-50% cases of DHF. Thrombin time is prolonged in severe cases. BT and CT are prolonged..
I. Platelet function is impaired and reduction of complement specially C3 is seen.
J. Other common findings are – Hypoproteinaemia, hyponatraemia and raised serum asparate aminotransferase. In shock there is metabolic acidosis with raised blood urea nitrogen.
K. X-ray chest may show pleural effusion (right side). In shock there is bilateral pleural effusion.
2.Virus and serological test
L. Isolation and detection of virus – Since all patients have a period of viraemia, the virus can be isolated in the course of the disease.
Detection of dengue virus by culture is definitive diagnostic test though practically it has many limitations. As antibody develops within days and the virus being heat labile collection and transport of specimen need care. Detection of dengue RNA using specific oligonucleotide primers, reverse transcriptase and thermostable polymerase – a test known as reverse transcription polymerase chain reaction (PCR) amplification assay is useful. The plasma , serum or cell can be used for this. Determination of virus and antibody type is preferable. Inoculation of clinical specimen to adult or larval mosquito is used for virus culture.
M. MAC ELISA Test: In primary and secondary dengue infection ELISA can measure the rise of specific IgM collected in the acute phase. Four fold rise of Ig G and IgM antibody is diagnostic.
N. Haemagglutination inhibition (HI test) – useful for diagnosis.
O. Neutralization Test: Most sensitive and specific test is serum dilution, virus constant, plaque reduction test. Following primary infection specific neutralizing antibody is seen in early convalescence. Following secondary infection high titre neutralizing antibody is produced against at least 2 or all 4 serotypes.
P. Dot bolt immuno assay: Now technique under consideration.
Q. Complement Fixation Test (CFT) : Though less sensitive it appears later than IgM or HI antibody but more specific . Useful for confirmation in later period. A 4 fold rise of CFT antibody where the interval between acute and convalescent is < 2 weeks signifies secondary seroresponse pattern.
R. Dengue virus antigen is autopy tissues may also be detected by immunohistochmistry, immunofluroscence.
In the early febrile phase DHF/DSS a wide spectrum of viral, bacterial, parasitic infections are to be taken into consideration. Chikungunya fever is difficult to differentiate from dengue clinically. But by 3-4 days the laboratory findings will establish dengue. Shock never occurs in Chikungunya. Thrombocytopenia and haemoconcentration excludes endotoxic shock.
Chikengunya fever (compared to DF)Duration of fever - < 7days
Haemorrhage - Less
Gn bleedig - 0
Haematemesis /Melana - 0
Shock - 0
Coma - 0
Abnormal reflux - 0
Hepatomegaly/palyarthralgia - more
. The major pathological abnormality in DHF/DSS is increased vascular permeability leading to loss of plasma volume. The major haemostatic changes in DHF are vascular changes (due to short acting mediators), thrombocytopenia and disorder of coagulation which leads to DIC and haemorrhagic complications.
. Early and effective replacement of plasma by plasma expander or fluid and electrolyte correction leads to favourable outcome even DSS may be reversible. Resuscitation from shock, correction of acidosis have good prognosis.
. Repeated Haematocrit and platelet count during illness is essential to assess signs of deterioration.
. DHF – Oral hydration with electrolyte is encouraged. Antipyretics are to be avoided to prevent acidosis, bleeding and Reye and Reye like syndrome. Paracetamol is preferable. Parenteral IV fluid is indicated if vomiting or hypotension. Bicarbonate containing IV fluids should be avoided initially. Vital signs, urine output are to be monitored.
. Calculation of maintenance of IV fluid
Body Weight Maintain volume (ml) over 24 hours
10 Kg 100/kg
10-20 Kg 1000+50 for each kg in excess of 10
>20 Kg 1500+20 for each kg in excess of 20
Total fluid required = +10ml /1% normal body weight loss
It is a medical emergency. Immediate IV fluid or plasma expander are given. Hyponatremia and metabolic acidosis are to be corrected. Sedatives may be indicated if patients is restless. Avoid hepatotoxic and long acting drugs. A single dose of chloral hydrate (12.5 –15mg /kg) orally is preferable. Oxygen therapy is given if needed. Blood transfusion – indicated when there is internal haemorrhage. Fresh whole blood is preferable. Fresh frozen plasma or concentrated platelets indicated is coagulopathy
. To be given or done - Rest, Fluid/Electrolyte and Acetaminophen.
. Not to be done or given - Aspirin, Brufen, IV therapy before haemorrhage, Blood transfusion, Antibiotic, No injection and No steroid.
PREVENTION AND CONTROL
. Killing of adult mosquitoes by space spray. Theramal fog (insecticide +oil), ULV aerosal (cold fog) and mist. Insecticide used as – Malathion, Fenitrothion, Fenthion, Pyrethroids
. Control of mosquito bite: using repellant oil, use of full clothing, mosquito net
. Eliminate breeding site: Spray larvicides like Temephos sandgranules and insect growth regulator Methoprine in form of brequets.
. Biological control by using Bacillus thurigienisis – H-14 BTI.
. No vaccine yet available.
. Health education,environmental sanitation is best way for prevention.
Dengue fever is one of the commonest arthropod borne viral haemorrhagic fever found in tropical or subtropical countries worldwide. The vector has close proximity to human. The virus has 4 serotypes out of which serotype 2 is dangerous. Dengue fever may lead to DHF or DSS depending on the serotype, adequate early treatment and host response. Dengue fever may simulate other fevers specially Chikungunya fever. The pathophysiology of DHF and DSS is increased vascular permeability, haemoconcentration and disorder of haemostasis including thrombocytopenia. The diagnosis depends on clinical symptoms and signs with laboratory findings and commonly thrombocytopenia, rise in haemotocrit value. Virus can be detected on culture. Different serological test are helpful to establish the diagnosis. The treatment is symptomatic with special emphasis in maintaining fluid and electrolyte balance. The measures to eradicate the vector is best prevention.
In tropical and subtropical countries the menance of Dengue is a constant feature. Epidemics occur very often with high morbidity and mortality . Early proper diagnosis, adequate management of DHF and DSS decreases the mortality. Control of mosquitoes and environmental sanitation is best way to prevent the disease.