Histoplasmosis

Question 1

Histoplasmosis capsulatum

Answer 1

DIMORPHIC FUNGUS
Temperate/subtropical environments
Grows best in nitrogen-rich organic material such as bird or bat excrement
Isolated from 31 states –> mainly around major river valleys

Question 2

Epidemiology

Answer 2

Similar to blasto 
--Big difference = size. Blasto = BIG. Histo = small 
Mycelial stage 
--free living in soil produces spores 
Microconidia = source of IFX to animals

Question 3

Mode of IFX

Answer 3

Inhale microconidia –> terminal bronchioles –> convert to yeast stage at 37C (divide by budding) –> phagocytosed by mononuclear cells (divide) –> dissemination (blood, lymph)

• -Some IFX confined to resp system
• -Most P: cell-mediated immunity controls IFX
• -GI dz can occur w/o resp IFX –> CAN BE INGESTED TO CAUSE INFECTION!!!

Question 4

Clinical Findings

Answer 4

Young <4yr
Working breeds?
Systemic signs common: inapp, WL, fever unresponsive to ABX
Resp signs: dyspnea, cough, harsh lung sounds
–Can be only signs!!!

Question 5

Other CS

Answer 5

GI signs = very common
--usually large bowel diarrhea 
--Severe wgt loss 
Liver, increased LN, increased spleen - infrequent 
Ocular skins, CNS - rare

Question 6

Lab Findings: CBC

Answer 6

Normocytic, normochromic non-reg anemia (chronic disease)
Leukocytosis variabke
Stress leukogram usual
Organisms in cells - rare - bunch of grapes crowding out a macrophage

Question 7

Lab findings: chemistry

Answer 7

Unremarkable in dogs w/ resp dz only
Marked hypoalbuminemia (PLE, blood loss)
Later in disease - also see increased globulins
Increased liver enzymes

Question 8

How clinically distinguish blasto from histo?

Answer 8

Histo produces enlargement of bronchial LN. Blasto does not

Question 9

Cytology

Answer 9

Organisms numerous in affected tissues - aspirate cytology
Lung aspirate, rectal scrapings, skin scrapes
BM may contain organisms when other sites fail
RBC phagocytosis

Question 10

Dx Isolation

Answer 10

Mycelia phrase 7-10d at room temp

Microconidia in culture very infectious

Question 11

Dx immunodiagnosis

Answer 11

Intradermal skin test unreliable in dogs

Serology also unreliable - often false negatives

Question 12

Therapy

Answer 12

Pulmon form may be self limiting - no Tx?
Chemotherapy recommended as dissemination occurs early in infection
Dogs w/ hilar lymphadenopathy - tx with steroids for a few days
Most req 4-6mo of itraconazole

Question 13

Therapy drug choices - itraconazole

Answer 13

Drug of choice but that may be changing

• -does not penetrate ocular or CNS well
• -Cats seem to improve in spite of this
• -Severe dz: combo of AMB induction followed by itraconazole

Question 14

Therapy drug choices - fluconazole

Answer 14

Many use as first choice because cost has come way down
–Penetrates CNS and ocular tissues well
Use in patients refractory to AMB, itraconazole

Question 15

Prognosis

Answer 15

Pulmonary form: fair to excellent
Dissemination: fair to good
GI dz: fair
Ocular or CNS involvement: poor

Question 16

Public Health

Answer 16

Transmission from animal –> animal not reported
–has been reported for blasto
Lab cultures infectious to man