24 - Vector Borne Diseases Flashcards
Sporozoite
Infective stage from mosquito salivary gland
Hypnozoite
Dormant or slow-developing trophozoite of P. vivax
Schizont
Asexual, multiple fission stage in liver or blood
Merozoite
Product of schizont
Trophozoite
Asexual form in red blood cells
Microgametocyte
Male gametocyte producing microgametes
Exflagellation
Process of forming microgametes from microgametocyte
Macrogametocyte
Female gametocyte producing macrogametes
Zygote
- Fertilised ovum
- Fusion of micro and macrogametes
Ookinete
Motile zygote
Oocyst
- Zygote with cyst wall
- Produces sporozoites
Romanowsky stain
Mixture of dyes used to stain blood film of malaria
Schuffer’s dots
Pinkish, small round stippling: P. vivax & P. ovale
Incubation period
Interval between infection and first clinical manifestations
Pre-patent period
Minimum time between infection and appearance
of parasite in RBC
Relapse (recurrence)
Renewed manifestation of infection due to invasion of RBC by hynozoite
Recrudescence
Renewed manifestations of infection due to survival of
blood form
Latency
Duration between primary attack and relapse
Paroxysms
Bouts of malarial fever (cold, hot and sweating stages)
General characteristics of Malaria parasite
- Obligate intracellular blood sporozoan parasite
- Primarily tropical and sub tropical
- Five human pathogenic species
Examples of human pathogenic species of malaria
- Plasmodium falciparum
- Plasmodium vivax
- Plasmodium malariae
Species differentiation of malaria
- Morphology and staining characteristic of various stages
- Number of merozoites in blood schizont
- Appearance of infected blood cell
- Pathology
Human liver stages of life cycle of Plasmodium species
Exo-erythrocytic cycle:
1. Mosquito takes a blood meal (injects sporozoites)
2. Infected liver cell
3. Schizont
4. Ruptured schizont
Human blood stages of life cycle of Plasmodium species
Erythrocytic cycle:
5. Infect RBC
6. Ruptured schizont
7. Gametocytes
8. Mosquito takes a blood meal (ingests gametocytes)
Mosquito stages of life cycle of Plasmodium species
Sporogonic Cycle:
9. Macrogametocyte enters microgametocyte, forming exflagellated microgametocyte
10. Ookinete
11. Oocyst
12. Ruptured oocyst, release of sporozoites
Distinctive features of Plasmodium falciparum
Banana shaped gametocytes and can effect any stage of RBC
Malaria transmission
- Infective bite of female Anopheles mosquito during blood meal
- Sporozoites injected via saliva
- Infection through blood transfusion recorded, doesn’t cross placenta
Malaria pathogenesis/clinical features
- Results from infection of, and repeated cycles of replication in blood cells of susceptible host
- Infected blood cells less deformable, sticky, carry less oxygen
- Adhere to lining of blood vessels (blockage)
- Massive destruction of blood cells (release toxic debris)
Malaria diagnosis
- Detection of early trophozoites (ring stages) and gametocytes in blood especially during febrile paroxysm
- Immunochromatographic tests
- PCR based tests
Prevention of malaria
- Control of vector by spraying insecticide
- Barrier methods (bed nets at night)
- Mass survey and chemotherapy and/or
chemoprophylaxis - Vaccine
How many protozoan diseases of man do we have
a vaccine for
1 (malaria, 18-36% efficacy)
Malaria treatment
- Excessive use of chloroquine led to widespread resistance
- Frequent doses of antibiotics (doxycyclin) used as prophylaxis
General characteristics of Babesiosis
- Obligate intracellular blood sporozoan
- Infection transmitted by ixodid ticks
- Significant veterinary pathogen
- Haemolytic anemia in animals
Diagnosis of Babesiosis
- Thin blood films, similar to malaria but get ‘Maltese cross’
- Serological: Detect IgG and IgM, help differentiate to malaria
- PCR based tests
Kinetoplastid diseases
All belong to a specialised group of protozoan parasites that are recognisable by the specialised single mitochondrial body (Kinetoplast)
Examples of Kinetoplastid diseases
- Leishmaniasis
- Chagas’ Disease
- Sleeping sickness
General characteristics of Leishmaniasis
- Visceral (systemic infection, fatal unless treated)
- Mucosal (progressive chronic destruction)
- Cutaneous (usually self healing, scaring)
- Diffuse cutaneous leishmaniasis is incurable
- Post Kala Azar Dermal Leishmaniasis
Leishmania species
Obligate digenetic protozoal parasites that have a mammalian host and sand fly vector
Leishmania life cycle in mammals
- Metacyclic promastigotes transferred during feeding
- Metacyclic promastigotes invade macrophages or granulocytes
- Promastigotes transform into amastigotes and multiply by simple division
- Asmastigotes leave infected cells, infect new macrophages and are transferred to sandfly
Leishmania life cycle in female sandflies
- Amastigotes released into the midgut
- Amastigotes transform into procyclic promastigotes
- Procyclic promastigotes by simple division change into metacyclic promastigotes
- Promastigotes migrate to pharyngeal valve
Causative agent of visceral leishmaniasis
Leishmania donovani complex
Visceral leishmaniasis symptoms
- Fatal
- Onset of disease is gradual
- Patients have a depressed cell mediated immunity
- Death due to haemorrhage or secondary infection
- Complete recovery leads to long lasting immunity
to re-infection (due to persistent parasites) - No vaccines, prophylaxis or multi drug therapy
L. major
Acute infection with a 3-6
months duration, wet lesions
L. tropica
Chronic disease, lasts for a
year or longer, dry lesions that ulcerate
L. aethiopica
Chronic disease often difficult to treat, dry lesions
Treatment of Leishmaniasis
- Anti leishmanial drugs all toxic
- High levels of drug resistance
- Pentavalent antimony
Chagas’ disease
- Trypanosoma cruzi
- Parasites in heart muscles leading to cardiac failure
- Parasites in nervous system leads to loss of control of alimentary canal
- No treatment for chronic diseases
- No vaccine or prophylaxis
Trypanosoma cruzi life cycle in human
- Triatomine bug takes blood meal (passes metacyclic trypomastigotes in feces )
- Metacyclic trypomastigotes penetrate various cells at bite wound cite and transform into amastigotes
- Amastigotes multiply by binary fission in cells of infected tissues
- Intracellular amastigotes transform into trypomastigotes then burst out of cell and enter blood
Trypanosoma cruzi life cycle in triatomine bug
- Triatomine bug takes blood meal (trypomastigotes ingested)
- Epimastigotes in midgut
- Multiply in midgut
- Metacyclic trypomastigotes in hindgut
African trypanosomes
- Haemoflagellates of Africa
- Vector-borne, confined to
where the vector, (tsetse fly)
breeds - Causes African sleeping sickness
African trypanosomes stages
- Various stages: in
insect or blood - Only trypomastigote, the typical, slender form occurs in human
- Inhabits blood, lymph
nodes, cerebrospinal
fluid
Pathogenesis/clinical features of T. gambiense
- Inflammation at site of
inoculation - 3 progressive stages (blood, lymph
nodes and CNS) - Fever with headache
- Daytime sleeping
- Coma
- Death in years
‘miracle drug’ effective against T. gambiensie
Eflornithine
