Dengue fever

Etiology: Dengue virus

 there are totally 4 serotypes in it namely 1,2,3,4

Transmission: Aedes aegypti 

Clinical features: Fever- high-grade type,  Myalgia- - joint pain (Break bone fever), Petechiae

Presence of rash and bleeding manifestations.

Stages of the disease
Dengue fever
Dengue hemorrhagic fever
Dengue shock syndrome

Complications
Disseminated intravascular coagulation
Shock

Laboratory Diagnosis
Complete blood count
Platelet count - decreased (Thrombocytopenia)
Confirmatory diagnosis
Detection of NS1 antigen by ELISA- can be detected as early as within 3 days of onset of fever
NS1 is a non-structural protein present in the dengue virus, hence the method is antigen detection and indicates current infection, but the same type is shared with other viruses like chikungunya hence makes it less specific.
Detection of IgM antibodies by Elisa - This is more specific and indicates current infection
Detection of IgG antibodies by Elisa- The presence of this indicates past infection.
If all three are positive then its an indication that the patient is affected for the second time by a different serotype and there is a high chance that the patient is prone for complications.
Dengue viral load - Real-time PCR

Scrub typhus

Etiology : orientia tsutsugamushi
Transmission : mite ( larva )
Clinical features :
Fever
Myalgia
Petichiae
Presence of Eschar - at the site of bite of the mite

Complication
ARDS
Ascitis
Peritonitis
Acute renal failure

Laboratory diagnosis
 Total count - leukocytosis
Weil Felix test positive for OxK
IgM ELISA
Immunoflurescence - antigen detection

Cholera

Clinical features
Rice watery stool (painless)
Severe dehydration  with following features
Tready pulse
Sunken eyes
Skin turgor decreased
Low blood pressure
Causative agent: Vibrio cholerae

Laboratory diagnosis
Stool sample for culture

Stool sample inoculated into alkaline peptone water and hanging drop done after 6 hrs

Hanging drop showing darting motility is suggestive of Vibrio cholerae

Then the broth is plated onto TCBS and MacConkey
After overnight incubation
TCBS- yellow coloured colonies
MacConkey- non lactose fermenting colonies 
Further identification 
Gram stain - gram negative curved bacilli
Oxidase- positive 
Indole- positive
TSI- A/A no gas and no H2S 
Citrate - positive 
Urease- negative
Mannitol - fermented 

Cholera red reaction - innoculate peptone water with few colonies of Vibrio cholerae
After overnight  incubation add few drops of concentrated H2SO4 along the sides of the test tube a red colour ring is formed indicating nitrosoindole ring 

Confirmatory test
Agglutination with antisera
1. Polyvalent O
2. Ogawa
3. Inaba
4. Hikojima

Diagnosis of melioidosis

Melioidosis
The disease has a insidious onset, fever for more than 3 weeks, body pain and loss of appetite
Multiple abscess in the lungs, liver, kidney and soft tissue

Caused by - Burkholderia pseudomallei

Diagnosis
Mainly based on the culture of blood,urine or pus from abscess


Identification of the organism is based on the following
Grey moist colonies on blood agar with metallic sheen which has a crumbled paper appearance on 48 hrs of incubation
Gram stain reveals - safety pin appearance of the gram negative bacilli
Mac Conkey agar - non lactose fermenting colonies crumbled paper appearance 

Oxidase positive
Indole negative
TSI - k/k no gas,no H2S
Citrate positive
Urease negative
Mannitol motility- fermented, motile
OF glucose      Oxidatively utilised
OF mannitol              "
OF lactose                 "
OF maltose                "
Arginine de hydrolysed

Polymyxin B (300units) - resistant


Treatment
 Cotrimoxazole is the drug of choice given over a period of 6 months
In severe cases carbapenems are the drug of choice

Diagnosis of Malaria

Clinical features
Fever with chills and rigors
Type of fever: Intermittent---

quotidian fever as an intermittent fever that occurs each day,

Tertian (fever every third day) 

quadrant(fever every 4 days)

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Splenomegaly
Haematuria
Jaundice

Caused by

P. vivax, P. falciparum, P. ovale, P. malariae

Transmitted by the bite of culex mosquito

Laboratory diagnosis
Peripheral smear - leishman's stain for the detection of the parasite ( gametocytes/ring forms and schizonts)

Multiple ring forms are seen specifically only in P.falciparum.

ICT test for detection of the LDH or Histidine rich protein II from blood
Quantitative Buffy coat test

diagnosis of anthrax

Patient usually presents with the following clinical features

Fever acute onset

Edema due to lymphaatic obstruction

Malignant eschar (vesicle ruptures , forms a ulcer and is covered by a scab which is black coloured and is surrounded by erythema ), the eschar is painless and the fluid inside is usually serosanguinous.(blood tinged)

Bleeding manifestaions

Meningitis usually haemorrhagic

Types of manifestation : cutaneous anthrax: which is usually non fatal resolves

                                     intestinal anthrax: due ingestion of the carcasses of the infected animal

                                     pulmonary antharax : due to inalation of the spores

Laboratory diagnosis

Blood culture is very sensitive- colony morphology- Blood agar- non haemolytic greyish dry colonies with serrated edges.

Nutrient agar - Medusa head appearance can be visualized in the edges of the colony with the help of the inverted microscope.

gram stain of the culture -thick gram positive bacilli with bamboo stick appearance

Demonstration of the capsule - polychrome methylene blue staining is done. (thick blue coloured bacilli surrounded by a pale pink coloured amorphous material)

Smear from the in-duration beneath eschar or the fluid from eschar

Smear shows thick gram positive bacilli with bamboo stick appearance

Direct fluroscent antibody testing detection of capsule

ELISA for toxin detection

Typhoid fever

Clinical features

Symptoms
Fever ( usually high grade)
        has a step ladder pattern i.e. temperature keeps on increasing and does not come down.
Vomiting
Abdominal pain

Signs
the patient has a coated tongue 

There is relative bradycardia( meaning high temperature but the heart rate is low)
hepatomegaly
The child usually presents with failure to thrive

Causative agent: Salmonella Typhi, Salmonella Paratyphi A, B, C

Diagnosis

Blood culture is the gold standard

positivity is 80% -90% in 1st week of fever
60%-70% in the 2nd week
<50% in 3rd week
 Bone marrow culture is most sensitive

Widal test Antibody detection( non- specific test)
it is positive by the end of 1st week
Urine culture is positive by the 3rd week of fever

Treatment
Third-generation cephalosporins are the drug of choice
(Tab.cefexime 200 mg twice daily for 7 days )

Complications
Intestinal hemorrhage and perforation
Septicemia
Meningitis