Bloodstream: Viral Hemorrhagic Fever, Malaria Flashcards
Viral hemorrhagic fever are caused by
- Arboviruses: dengue, yellow fever viruses
- Filoviruses: Ebola, Marburg viruses
- Rodent borne viruses: Hantaviruses, arenaviruses
Common features of viral hemorrhagic fever
All are enveloped RNA viruses
Humans are not the natural reservoir
Symptoms: fatigue, 🤒, weakness, dizziness 😵💫, muscle aches
Only symptomatic treatment except for Lassa fever
No vaccine except for yellow fever and dengue
Arboviruses of India
1. Hemorrhagic fever group: Dengue, KFD 2. Fever with arthralgia: Chikunguniya 3. Encephalitis: Japanese encephalitis and West Nile encephalitis
Dengue
vector
Aedes aegypti (or A. albopictus)
Bite during day time
Nervous feeder (bites repeatedly to more than one person to complete a blood meal) ➡️ efficient vector
But A. albopictus is aggressive and concordant feeder.
Extrinsic incubation period of 8-10 days for infectivity, but then for life
Transovarial transmission
Dengue virus
basic pathogenesis
- 1° dengue infection:
When a person is infected for the first time with any one serotype - 2° dengue infection:
Months to years later when the person is infected with a different serotype
Dengue
antibody response
- Neutralising: protective
Against infective serotype: lifelong immunity
Against others: diminishes over few months - Non-neutralising: protects the serotype
Heterotypic, i.e, produced serotypes except the infective one
It inhibits bystander B cell activation - ADE antibody dependent enhancement
➡️ mononuclear cell recruitment and cytokines release
Dengue fever
according to traditional classification
1. Abrupt onset of high 🤒: biphasic/break bone/ saddle back fever 2. Maculopapular rashes over chest and upper limbs 3. Severe frontal headache 4. Muscle and joint pain 5. Lymphadenopathy 6. Retro-orbital pain 7. Loss of appetite, nausea, weakening
DHF Dengue hemorrhagic fever
- High grade continuous fever
- Hepatomegaly
- Thrombocytopenia
- Raised hematocrit by 20%
- Evidence of hemorrhages
Dengue shock syndrome
All the criteria of dengue hemorrhagic fever +
- Rapid and weak pulse
- Narrow pulse pressure
- Presence of cold and clammy skin
- Restlessness
2009 WHO classification of dengue
- Dengue with or without warning signs
2. Severe dengue
Dengue
factors determining the outcome
- Infecting serotype:
Type 2 is apparently more dangerous - Sequence of infection:
Serotype 1 followed by serotype 2 can develop into DHF and DSS more often - Age: Children less than 12 yr are more prone to develop DHF and DSS
Dengue during pregnancy
Perinatal transmission of dengue infection can occur
Newborn may present with fever, thrombocytopenia, ascites or pleural effusions
Typically on first week of life
Dengue
antigen detection
NS1 antigen detection
ELISA and ICT are used
Becomes detectable from day 1 of fever upto 18 days
Highly specific: differentiate b/w flaviviruses and also b/w different serotypes
Dengue
antibody levels in 1° infection
Antibody response is low and of low titre
IgM appears after 5 days of fever and disappears within 90 days
IgG is detectable at low titre in 14-21 days of illness and then slowly increases
Dengue
antibody levels in 2° infection
IgG rises rapidly:
• Often cross-reactive and may give false positive result after recent infection of vaccination with yellow fever or JE.
• Low levels remain detectable for over 60 years and is a useful indicator of past infection.
IgM is significantly low and may be undetectable
The recommended serological test for dengue in India
MAC-ELISA: Antibody capture ELISA
Double 🥪 ELISA detecting IgM, then serotype specific envelop protein antigen detection
(Signal enhancement by avidin-biotin complex ABC)
Limitation: Cross reactivity with other flaviviruses
Most specific but cumbersome serological tests for dengue
Plaque reduction test
Micro neutralisation test
Most specific test for dengue
Detection of specific genes of viral RNA (3’-UTR) by real time RT-PCR.
Most sensitive and specific
Detected in blood -1 to +5 days of onset of symptoms
Treatment of dengue
No specific antiviral therapy Symptomatic treatment like: 1. Replacement of plasma losses 2. Correction of electrolyte and metabolic disturbances 3. Platelet transfusion if needed
Dengvaxia
CYD-TDV
Age: 9-45 years
Only in people previously infected with dengue
Not yet available in India
Chikungunya
virus and its transmission
Togaviridae family
Enveloped ss RNA viris
Spread via Aedes aegypti mainly
Rarely vertical transmission from mother to foetus or organ transplantation
Chikungunya
transmission cycle
- Urban cycle:
b/w humans and Aedes aegypti which bites during daytime - Sylvian/ jungle cycle:
b/w 🐒 and forest species of Aedes
Chikungunya
acute clinical manifestations
Incubation: around 5 days
• 🤒 and severe joint pain worsened at morning
• Arthritis is polyarticular, migratory, edematous, mainly affecting small joints of wrist and ankles
• Other symptoms are headache, muscle pain, tenosynovitis or morbiliform skin rashes
• Chik sign out brownie nose appearance
Most patients recover within a week, except for joint pain
Chik disease or brownie nose appearance
Rarely seen in Chikungunya
Hyperpigmentation of centrofacial area
Due to 🔼 intraepidermal melanin retention triggered by Chikungunya
Chikungunya
high risk group
- Newborns
- Older adults >65 years
- Underlying hypertension, diabetes, or heart disease
Only supportive treatment
Chikungunya
antibody changes
IgM appears after 4 days of infection and lasts for 3 months
IgG appears only after 2 weeks but lasts for years.
So detection of IgM or 4-fold rose in IgG is more important.
Chikungunya
recommended test
MAC-ELISA: IgM antibody capture
Good specificity and sensitivity
Only little cross-reactivity with other alphaviruses and dengue
Chikungunya
laboratory diagnostic measures
- MAC-ELISA
- Molecular method: rt-PCR for nsP1, naP4 genes
- Viral isolation
- Haematological findings like leukopenia with lymphocytes predominance, elevated ESR and C-reactive protein
Kyasanur forest disease KFD
Family flaviviridae
Enveloped ssRNA virus
Hard ticks (Hemaphysalis spinigera) are the vector
🐒 , rodents 🐀 and squirrels 🐿 are common hosts (🐒 are the amplifier hosts)
Reported in drier months
KFD
clinical manifestations
Incubation: 3-8 days
1. First stage: hemorrhagic 🤒
Acute high 🤒 with malaise and frontal headache, followed by hemorrhagic symptoms; bleeding from nasal cavity, throat, gums and GIT
2. Second stage: meningocephalitis 7-21 days after first stage
KFD
Laboratory diagnosis
- Virus isolation
- IgM antibody detection by ELISA
- nested RT-PCR and real time RT-PCR have been recently developed to detect viral RNA
- Leukopenia, thrombocytopenia, 🔽 hematocrit, albuminuria and abnormal CSF in 2nd stage
Filoviridae
Pleomorphic, mostly appears as long filamentous threads
Most fatal along the viral hemorrhagic fever
Eg., Ebola, Marburg viruses
Ebola virus
transmission
- Close contact with blood, sections, organs or other body fluids of infected animals like chimps, 🦍, fruit 🦇 or 🐒.
- Human-to-human transmission:
Direct contact through broken skin or mucus membranes
Body fluid, infected surfaces and materials - HCW and family members/close contacts are at high risk
- Can stay in semen for 3 months, but sexual transmission unreported.
Ebola virus
clinical manifestations
Incubation: 2-12 days
🤒, headache, muscle pain and sore throat, followed by:
1. Abdominal pain, 🤮 and severe watery diarrhoea
2. Diffuse erythematous maculopapular rash, petechiae, ecchymosis/bruising; often leading to shock and death ☠️
Mortality: 25-90%
Ebola virus
antibody detection
ELISA detects both IgM and IgG separately by using recombinant nucleoprotein NP and glycoprotein GP antigens
IgM appears after 7 days of symptoms and lasts for 3-6 months
IgG appears after 14 days and lasts for 3-5 years
Other Ab detection assays include IFA and Ab-phage indicator assay
Ebola virus
serum antigen test
electron microscopy 🔬
Detected by ELISA
The target proteins are: NP, VP40, GP
IHC staining and histopathology can also be used to localise viral Ag in tissue
e- 🔬: topical filamentous viruses can be seen
Ebola virus
molecular methods
RT-PCR and real time RT-PCR assays are useful to detect specific RNA such as NP and GP gene 🧬.
Virus 🦠 can be detected 3 days after onset of 🤒 and remains positive for 2-3 weeks
Ebola virus 🦠
Prevention
- Proper infection control and sterilisation (😷 and🧴)
- Isolation
- Avoid direct or indirect contact with blood, body fluids and secretions
- Avoid attending ⚰️ or wear PPE
- Monitoring for 21 days after returning from outbreak area
Marburg virus 🦠
Viral hemorrhagic fever
Reported in Africa
Latest outbreak in Angola with 252 people affected and mortality rate of 90%
Rodent borne viruses
Rodent borne viruses or roboviruses are transmitted from rodents to man by contact with infected body fluids or excretion.
They are maintained in nature by transmission from rodent to rodent and without participation of arthropod vectors.
Major rodent-borne viruses include: Hantaviruses and Arenaviruses
Hantaviruses
Virus
Diagnosis
Family Bunyaviridae
Spherical, enveloped viruses containing triple segmented, negative ssRNA.
Diagnosis is by detection of viral RNA by RT-PCR
Hantaviruses
Clinical manifestations
- Hemorrhagic fever with renal syndrome HFRS:
But several members such as Hantaan 🦠, Dobrava 🦠, Puumala 🦠 and Seoul virus - Hantaviruses pulmonary syndrome:
By Sin Nombre virus
Arenaviruses
Pleomorphic, 50-300 nm in size, enveloped with large, club shaped peplomers and contain a segmented ssRNA.
Grouped into: New world viruses and old world viruses
Classification of Arenaviruses
- New world viruses:
Include Junin, Machupa, Guanarito and Sabia viruses.
They cause South American hemorrhagic fever - Old world viruses:
• Lassa viruses: hemorrhagic fever in Africa
• Lymphocytic choriomeningitis LCM viruses: primarily infect 🐁, rarely causes meningitis in humans
Malaria is caused by
- P. vivax
- P. falciparum
- P. ovale
The above 3 are tertian - 48 hrs - P. malariae: quartan - 72 hrs
- P. knowlesi - quotidian 24 hours
Malaria
cases where sporozoite not the infective form
Trophozoite (or merozoite) is the infective form when it is rarely transmitted through blood transfusion or transplacentally
Malaria
stages of pre-erythrocytic (hepatic) phase
- Sporozoites leave the circulation in 30 min
- Attachment to hepatocyte receptors and entry
- Trophozoite formation and feeding
- Schizogony: several nuclear divisions to form pre-erythrocytic schizont containing several merozoites
- Rupture of hepatocyte to release merozoites.
Malaria
special points about pre-erythrocytic (hepatic) phase
- Circumsporozoite proteins involved in attachment to hepatocyte
- Negligible liver injury
- Lasts for 5-15 days
- Hypnozoites
Hypnozoites
Some sporozoites of P. vivax and P. ovale do not develop further and may remain in liver as hypnozoites and may cause relapse after many years which should be differentiated from recrudescence
Malaria
special points about erythrocytic phase
- Merozoites bind to glycophorin receptors on RBC, endocytosis and then in parasitophorous vacuole.
- Early trophozoites (ring form)
- Late trophozoite or amoeboid form
- Hemozoin formation
- Schizogony to form 6-30 erythrocytic schizont
- RBC rupture ➡️ malarial paroxysm
Malaria
early and late trophozoite
- Early trophozoite or ring form:
Annular or signet ring in appearance containing a central vacuole with a peripheral thin rim of cytoplasms and nucleus
It enlarges and becomes more irregular to form - Late trophozoite or amoeboid form:
It undergoes schizogony to produce 6-30 daughter merozoites (erythrocytic schizont) arranged as rosette which can invade other RBCs
Why in P. falciparum only ring forms are seen in peripheral blood examination
In P. falciparum, the later stages of erythrocytic cycle occur in capillaries of brain and internal organs.
Malaria
gametocytes
Some merozoites transform into round microgametocyte and macrogametocyte (except falciparum where it is 🌙 or 🍌 shaped)
They are capable of transmission only when they are mature, viable and present in sufficient density.
Malaria
mosquito 🦟 cycle
- Microgametocyte undergoes exflagellation and divided into 8 flagellated actively motile bodies called male gametes
Macro gametocyte directly develops into one macrogamete. - Zygote
- Ookinette: motile elongated formed in midgut
- Oocyst
- Sporozoite formation by meiosis
- Release and migration to salivary gland
This in total extends 1-4 weeks (extrinsic incubation period)
Oocyst, ookinette and sporozoites of malaria in 🦟
Ookinette: motile elongated formed in midgut
Oocyst: ookinette penetrates stomach wall becomes rounded and covered by a thin elastic membrane to form oocyst
Sporozoites: 4 spindle shaped sporozoites produced by meiosis
They are released and then they migrate to salivary gland’s
Benign malaria
Milder in nature Can be caused by all 4 species Characterised by triad of: 1. Febrile paroxysm 2. Anaemia 3. Splenomegaly due to macrophage proliferation to ingest RBCs
Stages of malarial febrile paroxysm
- Cold stage:
Lasts for 15 minutes to 1 hr
The patient feels lassitude, headache, nausea 🤢 , intense cold 🥶, chills and rigor - Hot stage:
Patient develops a high grade 🤒 of 39-41°C and dry burning skin
Head ache persists but 🤢🔽 - Sweating stage:
🤒🔽 with profuse sweating 😓
Skin becomes cold and moist, patient feels relieved 😌 and often 💤
Lasts for 2-4 hours
Deviations from benign malarial febrile paroxysm
- In P. falciparum, the 🤒 is more irregular or even continuous with marked prostration, headache and 🤢
- The classical paroxysm may not be always present due to maturation of generations of parasites at different times.
Causes of anemia in benign malarial fever
- Parasite induced RBC destruction
- Splenic removal of both infected RBC and uninfected RBC coated with immune complexes
- Bone 🦴 marrow suppression
Sequestration of P. falciparum
In deep visceral organs like 🧠, kidney,… by
Cytoadherence: binding of infected RBCs to endothelial cells by its antigen called P. f erythrocyte membrane protein PfEMP-1.
This leads to blockade of vessels, congestion and hypoxia of internal organs.
Also they avoid frequent spleen passage
PfEMP-1 undergoes frequent antigenic variation.
Complications of falciparum malaria
- Cerebral malaria: most serious
- Pernicious malaria:
Black water malaria + algid malaria + septicemic malaria - Pulmonary edema and ARDS
- Hypoglycemia: 👶, 🤰, poor prognosis, following quinine Rx
- Renal failure
- Bleeding w/o DIC
- Severe jaundice: in adults
- Severe normochromic, normocytic anemia
- Acidosis
Black water anemia
Sudden intravascular hemolysis followed by fever, hemoglobinuria, and dark urine
1. Occurs following quinine treatment to previously infected falciparum patients
2. Ab develop against parasitised and quininised RBC.
Later immunocomplex formation followed by complement mediated massive destruction of parasitised and normal RBCs.
Algid malaria
Septicemic malaria
Algid malaria: cold clammy skin, hypotension, peripheral circulatory failure and profound shock.
Septicemic malaria: high-grade 🤒 with dissemination of parasite to various organs leading to multiorgan failure.
Chronic complications of malaria
- Tropical splenomegaly syndrome/ hyper active malarial splenomegaly
- Quartan malarial nephropathy:
immunocomplex deposition in glomeruli by P. malariae - Promotes Burkitt’s lymphoma:
Due to immunosuppression.
Tropical splenomegaly syndrome
Hyperactive malarial splenomegaly
Due to abnormal immunologic response to repeated malaria infections and characterised by 🔼 IgM.
Patients respond well to anti-malarial chemoprophylaxis
Special features of transfusion malaria (which includes needle stick injury, organ transplantation)
- The infective form can be intra-erythrocytic forms but not gametocytes.
- There is no pre-erythrocytic stage and no relapse ➡️
- Radical chemotherapy with primaquine is unnecessary.
- Incubation period is often short
Malaria in pregnancy
It increases risk of fetal distress syndrome and can result in premature labor, low birth weight and still birth.
In areas of high malarial transmission, 🤰 are particularly susceptible to severe anemia, hypoglycemia and acute pulmonary edema.
Innate immunity of malaria depends on:
1. Age of RBC: vivax and ovale attacks young RBC malariae attacks older RBC 2. Nature of hemoglobin ✖️ falciparum 3. Hereditary ovalocytosis are resistant 4. G6PD deficiency 5. Duffy negative RBC Duffy blood group acts as receipts for P. vivax 6. Age: children are more prone but not infants 7. Nutritional status: paradoxically
Malaria
acquired immunity
1. Humoral immunity: Against both asexual and sexual forms 2. Cell mediated immunity 3. Premunition/ incomplete: Immunity against Plasmodium remains till original infection is active
Transmission of malaria is proportional to:
- Density of vector and no. of human bites per day per 🦟
- Time of 🦟 bite, more after dusk
- 🦟 longevity for sexual development of plasmodium
- Optimal temperature, humidity (60%) and rainfall
Malaria
microscopic tests
- Peripheral blood smear: gold standard
• thick smear: more sensitive
• thin smear: speciation can be done - Fluorescence microscopy - Kawamoto’s technique
Nuclear DNA stained green - Quantitative buffs coat examination:
Parasitised RBCs appear as brilliant green dots.
Malaria
speciation using thin smear - species wise
- vivax: amoeboid ring form and schizont
- falciparum: ring forms (multiple ring, accole and headphone shaped ring forms), 🍌 shaped gametocytes
- malariae: band forms
- ovale: enlarged fimbriated oval RBC with ring forms
Malaria
Peripheral blood smear - specimen
Site:
• great toe in infants
•👂 or finger prick in the rest
Capillary blood is taken few hours after height of paroxysm before anti malaria drugs
Smeared and stained by Romanowsky stain within 1hr
Examined twice to confirm absence
Malaria
features involved in speciation
- RBC size
- Pigments: prop. to severity
Dark brown except vivax (yellowish-brown) - Schizont
- Gametocytes:
🍌 shaped in falciparum - Ring forms
Malaria
RBC size vs species
Normal: falciparum, malariae
Enlarged: vivax
Enlarged and fimbriated margin: ovale
Malaria
speciation based on schizont
P. vivax: large, which completely fills the enlarged RBC
contains 12-24 merozoites/schizont.
P. malariae and P. ovale: small, fills 3/4th or bit more
contains 8 merozoites/schizont.
P. falciparum: schizonts are not seen
Malaria
ring forms and speciation
Ring forms are most important in speciation.
P. vivax:
• Rings are 2.5 μm, occupies 1/3rd
• late trophozoites are amoeboid shape
P. falciparum:
• rings are 1.5 μm, occupies 1/6th, maybe multiple/cell
• Accole form: ring attached to RBC membrane
• double-dot/headphone shaped ring form: nucleus fragmented
P. malariae:
• early trophozoites are similar to vivax
• late trophozoite is band shaped
P. ovale:
• similar to vivax, but in ovale shaped RBC
Malaria
rapid diagnostic tests RDTs detecting antigens
the antigens are:
Produced by all Plasmodium species: 1. Parasite lactate dehydrogenase pLDH 2. Parasite aldolase Produced by only P. falciparum: 3. Histidine rich protein-2: HRP-II
Malaria
Advantages of RDTs rapid diagnostic tests detecting antigens
- Sensitivity: at >100 parasites/μL they are sensitive, but not so much otherwise
- Prognosis: though not better than🔬
- Pregnancy: HRP-II is reliable marker to diagnose it in🤰
- Severity: intensity of band
Malaria
disadvantages of RDTs rapid diagnostic tests detecting antigens
- Speciation of non-falciparum species impossible
- Expensive than 🔬
- Gametocytes not detected
- Low sensitivity
- Not developed for knowlesi
Severe malaria treatment
DoC include: 1. IV artemisinin derivatives: Against sexual RBC stages and gametocytes 2. IV quinine: Against non-falciparum gametocytes
Anti-malarial drugs
1. Quinolines: Chloroquine, quinine, mefloquine, primaquine 2. Artemisinin and its derivatives 3. Atovaquone 4. Proguanil 5. Pyrimethamine 6. Sulfadiazine and sulfadoxine 7. Tetracycline and doxycycline
Factors contributing to emergence of anti malarial drug resistance
Treatment
- Longer half life of drug
- Mutation in parasite gene 🧬
- Inadequate and irregular usage of drug
- Host immunity
Rx: combination of drugs like ACT artemisinin combination therapy
Mechanisms of drug resistant malaria
- Chloroquine resistance:
Mutation in 🧬 encoding for transport proteins like PfCRT (chlq rs transporter) and PfMDR1 (multi drug rs 🧬 1) - Antifolate resistance: pyrimethamine
mutation of DHFR dihydrofolate reductase
Chemoprophylaxis for malaria
Is recommended for: travelers 🧳, migrant laborers, military 🪖 personnel.
Types:
1. Short term - doxycycline
2. Long term - mefloquine
Vector control strategies
Anti adult measures: 1. Residual spraying 2. Space application 3. Individual protection Anti larval measures: 1. Larvicide 2. Source reduction 3. Biological larvicide
Problems of making a malarial vaccine
- The vaccine 💉 candidates are poor inducer of CMI
- Antigenic variation in malarial antigens such as PfEMP
- Different immune mechanisms occur in different stages of malaria life cycle
