Potomac Horse Fever Neorickettsia risticii - NICUvet

Potomac H
Neoricketts

Horse Fever
sia risticii

• Potomac Horse Fev
• Equine Monocytic
• Equine Ehrlichial C
• Equine Ehrlichial A

Synonyms

ver (PHF)
Ehrlichiosis (EME)
Colitis (EEC)
Abortion (EEA)









Poto

• Subclinical infecti

Healthy horses
No history of illness

• Transient, low ant

Repeated exposure t
Cross reaction with

omac horse fever
Epidemiology

ion - 16-33%

s

tibody titers

to subinfective doses
other microbes

Poto
Seas

• Highest number Cl

July
August
September

• 70% of 900 clinic

omac horse fever
sonal Fluctuation

linically affected horses

cal cases in Maryland (5 yrs)





Poto
Clinical D

• Enzootic area

Frequent occurre
Low attack rate (

• Epizootic area

High attach rate

omac horse fever
Disease Sporadic

ence in area
(<5%) on farms

(20-50%) on farms





Poto
Montgom

Year Cas
1982 11
1983 11
1984 10

omac horse fever
mery County, MD

ses Farms
12 51
16 75
01 68





Poto

• Direct
• Insect v
• Oral

omac horse fever
Transmission

vector





Poto

• Vectors of other ehrli
• Only adult tick found

along the Potomac riv

Dermacentor variabilis

omac horse fever
Vector

ichial agents are ticks
d parasitizing horses
ver:

s





Poto
Derma

Larval and nymph stages fe
Attempts to transmit E. risti

field captured adult ticks
Larval and nymph stages fe

transmit to other mice or
Mice from endemic areas co
Dogs uniformly seronegativ

omac horse fever
acentor variabilis

eed on small ground mammals
icii to normal horses using
(D. variabilis) failed
ed on ehrlichemic mice will not
to ponies
onsistently seronegative
ve on endemic farms

Poto

• Dermacentor variabil
• Attempts to transmit h

Rhipicephalus sanguine
Ixodes scapularis
Amblyomma americanu

omac horse fever
Vector

lis is not the vector
have also failed with:

eus

um

Poto
N

• Ho
• Do
• Cat
• Go
• Pig
• Rab
• Fox

omac horse fever
Natural Infection

orse
og
t
oat
g
bbit
x

Poto
Tran

• Cat flea Ctenoceph
• Chigger mite Neot
• Hematophagous fli

Adult stable flies (St

omac horse fever
nsmission Studies

halides felis
trombicula whartoni
ies

tomoxys calcitrans)

Poto

• Ehrlichia shed into co
• Direct contact will no
• Concentration of the E

Neorickettsia helmintho
N. elokominica

omac horse fever
Oral Infection

olon
ot result in transmission
Ehrlichia in a vector

oeca

Poto
Or

• Survival o
• Concentra

Insects
Nematodes

omac horse fever
ral Transmission

outside host
ation

s

Cer
Operculate snails (P

Caddisflies (D

rcariae (fluke larvae),
Pleuroceridae: Juga),
Dicosmoecus gilvipes)



Caddisflies

Poto
Clinica

• Fever
• Depres
• Anore
• Ileus
• Colic
• Diarrh
• Lamin

omac horse fever
al Manifestations

ssion
exia

hea
nitis