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1

Arbovirus: general

Group of viruses transmitted by arthropod vectors

RNA virus

2

Arbovirus: three types of ticks

Blacklegged

Lone Star

Dog tick

3

Clinical syndromes of the mosquito-borne viruses

Systemic febrile illness

Fever with arthritis

Encephalitis

Hemmorrhagic fever

4

Alphavirus - 4 encephalitic viruses

Eastern equine encephalitis

Western equine encephalitis

Venezuelan equine encephalitis

Everglades virus

5

Eastern Equine Encephalitis

Eastern USA

Transmitted by mosquitoes

Bird reservoir

Can appear as an influenza-like illness or can be more severe encephalitis

Highest incidence of developing encephalitis (compared to WEE, and VEE)

6

Japanese Encephalitis Virus: general

Produces encephalitis with high mortality and morbidity

Positive sense ssRNA

5 genotypes

Affects mainly southeastern Asia

Transmitted by Culex mosquitoes

Pig and bird reservoirs - Pig reservoirs have high titer viremia

Two vaccines available

7

Japanese Encephalitis Virus: clinical features

Wide spectrum: from febrile headache to aseptic meningitis to encephalitis

Prodrome (2-3 days) - headache, fever, chills, anorexia

Acute (3-4 days) - High fever, seizure, unblinking eyes, rigidity, Tremor

Subacute (7-10 days) - Tremors, paresis, incoordination, lip smacking, rapid CNS changes

Poor prognosis - respiratoryy dysfunction, prolonged seizures and fever, albuminuria

8

Yellow fever virus: general

Divided into West and East African lineages

West African lineage spread by slave trade

Increased transmission in Africa due to decrease in vaccination

Seasonal incidence and geographic localization to tropical regions of Africa and South America

Transmitted by mosquitoes

Non-human primate reservoir

Adverse reactions to vaccine

9

Adverse effects to yellow fever vaccine

 

Immediate hypersensitivity - anaphylaxis

YF vaccine-associated neurologic disease

YF vaccine-associated viscerotropic disease

10

YF vaccine-associated viscerotropic disease

Febrile illness begins 3-5 days after vaccination

Clinically resembles naturally acquired yellow fever

 

11

Yellow Fever: clinical features

Incubation - 3-6 days

Can manifest as mild febrile illness or a fatal hemmorrhagic disease

Severe YF - fever chills, myalgia, nausea, vomiting, gingival hemmorrhages, epistaxes, faget's sign

12

Faget's sign

 

Presence of bradycardia despite a rising temperature

13

Yellow fever - hemmorraghic phase

Coffee-ground hematemesis, melena, petechiae and ecchymoses

Volume depletion

Renal failure - albuminuria, oliguria

Presence of jaundice, hypotension, azotemia, hypothermia, stupor, coma

Death - occurs on 7th-10th day

14

Yellow fever - convalescent phase

Prolonged

Can occur with asthenia

Elevated serum transaminase levels can persist after recovery

15

Dengue virus: general

Flavivirus

Most common arboviral disease in the subtropical and tropical regions

Transmitted by Aedes egypti mosquito

NO VACCINE

16

Characteristics of Aedes egypti mosquito

 

Urban

Breeds in standing water

Daytime feeder

Humans preferred host

17

Spread of dengue

Urbanization

Global warming

Population growth

18

Dengue fever: Primary dengue clinical features

2-7 day incubation

High fever, headache, lumbosacal pain, facial flushing

Fever lasts 6-7 days with myalgia, bone pain, nausea, vomiting, weakness

WBC count is depressed

19

Dengue fever: secondary dengue clinical features

 

Hemmorhagic fever

Petechiae, epistaxis, GI bleeding, positive tourniquet test, myocarditis, neurological disorders.

Prolonged convalescence with generalized weakness, depression, bradycardia and ventricular extrasystoles

 

20

Shock syndrome

Severe form of viral hemmorhagic fever

Results from: intravascular volume depletion and cardiovascular collapse

21

C. Tetani: bacteriology

 

Gram +ve
Environmental
Soil contamination of wounds beneath skin surface
Tetanospasmin- exotoxin
Locus of infection

22

C. Tetani: 4 types of disease

Neonatal - contamination of umbilical cord/no maternal immunization

Cephalic - Contamination of head wounds. Cranial nerve palsy

Local - Rigidity of a single muscl group

Generalized - full body symptoms/rigidity. Respiratory failure leads to death

23

C. Tetani: Tetanospasmin

Two subunit (AB subunit motif)

Large subunit opens pore in motor neuron and allows small subunit to enter

Small subunit travels via retrograde axonal transport

Inhibits motor neurons by cleaving synaptobrevin in inhibitory motor neurons of CNS

Loss of inhibitory activity on motor neurons leads to spasms

24

C. Tetani: Dx

Difficulty swallowing

Strong muscle spasms/paralysis

Lockjaw, risus sardonicus (grimace), opisthotonis (strong arching of back)

Spatula test - patient will bite down instead of gag

Lab: Tennis racket spores

25

C. Tetani: Treatment

Tetanus antitoxin - human sourced - neutralizes the toxin, shipped from CDC

Can use metronidazole as antibiotic

Airway support

Benzodiazepines to prevent spasms

26

C. Tetani: Prevention

Vaccination with tetanus toxoid

deep puncture wounds - cleaned and debrided - give vaccine booster

27

C. botulinum: Bacteriology

Gram +

Spore-forming

Environmental, food-borne botulism through alkaline vegetable

8 botulinum toxins - A and B are most toxic

28

C. botulinum pathogenesis

Bacteria die in gut, but exotoxin is readily absorbed and carried to peripheral nerve synapses

Cleaves synaptobrevin in stimulatory motor neurons of peripheral nerves

Prevents release of ACh and contraction of muscle - flaccid paralysis

Irreversible loss of function at affected nerve terminals

29

C. botulinum: less common presentations

 

Infant botulism - floppy baby and breathing problems

Wound botulism - Spores germinate in infected wound and secrete exotoxin

30

C. botulinum: Dx

Exam - History is important, nausea, vomiting, diarrhea, trouble swallowing, double vision, fized/dilated pupils

Lab - Culture not generally useful, test for toxin in suspected food/patient samples