Download HERPESVIRIDAE

RETROVIRIDAE.
Part IILENTIVIRUSES
PETER H. RUSSELL, BVSc,
PhD, FRCPath, MRCVS
Department of Pathology and
Infectious Diseases, The Royal
Veterinary College,
Royal College Street,
London NW1 OTU.
E-mail
Web site
Objective
Students should be able to:
• describe the differing immune-complex or
dysfunction diseases associated with these viruses:
Visna Maedi and caprine arthritis/encephalitis
virus, equine infectious anaemia, feline
immunodeficiency virus (FIV), bovine
immunodeficiency virus.
• compare and contrast the diagnosis and
pathogenesis of FIV and FeLV.
FELINE
IMMUNODEFICIENCY
VIRUS
Once considered to be a major cause of
lymphadenopathy and immunosuppression
in cats, but now field work shows this is
untrue. The virus is neither a death
sentence to cats. Nor zoonotic.
Pathogenesis and clinical signs:
1)Regressive transient infection
with no CD4 decline subclinical, most UK cases.
2) Typical, progressive CD4 decline, 3
idealised stages
Stage 1. High circulating virus for 1-10 weeks.
Lymphoid depletion as a result of virus infection and
destruction of double positive CD4CD8 Tcells.
Thymic aplasia (most important in kittens).
Stage 2. Asymptomatic carrier stage with a
decrease in circulating virus effected by CD8 cells
and polyclonal antibody. Paracortical T cells and
lymphoid follicles expand in lymph nodes, spleen and
thymus, this may be visible as white nodules.
3)Rapidly progressing infection
with high virus and rapid
depletion of CD4 cells in 40%
of cats after vaginal exposure
Clinical signs of virulent
viruses:
Weight loss, pyrexia, anaemia, stomatitis,
abortion, chronic rhinitis, recurrent cystitis,
vomiting, recurrent skin infections,
diarrhoea, abnormally high level of B cell
lymphomas - in combinations but not all
together.
Control:
No vaccine. Early experimental vaccines
exacerbated disease. If a cat is healthy and
positive get a confirmatory test done at
Glasgow. If the cat is positive then keep it
isolated. Addie now considers the cats
protection league's policy of killing any
healthy ELISA positive cat to be
unnecessary.
BOVINE
IMMUNODEFICIENCY
VIRUS
MAFF consider it to be absent from UK and
of little clinical relevance.
VISNA-MAEDI VIRUS (V-M V)
(or Maedi-Visna)
The virus: Isolates are neurotropic or
pneumotropic and cause chronic wasting
disease in sheep. Variants which escape
neutralisation arise during the infection (as
with HIV and Equine Anaemia Virus). Visna
= Icelandic for wasting; Maedi = Icelandic
for dyspnoea.
Immunity and epidemiology:
Infected animals remain carriers. Transmission
is via aerosol, milk, or colostrum. The crowded
6 month winter housing as practised in Iceland
allowed spread not only of V-MV but also of
Johne's disease and SPA.
Infection was introduced into the UK by French
exotic breeds and carriers occur in one third of
flocks containing imported sheep (particularly
Texel).
CAPRINE
ARTHRITIS/ENCEPHALITIS
VIRUS
This is caused by a distinct virus which is
serologically related to V-MV but has
antigenic and genetic differences in its
envelope. It causes an encephalitis of kids or
an insidious polyarthritis of adults.
EQUINE INFECTIOUS
ANAEMIA (EIA) (Swamp
fever)
EIA is an exotic type III immunecomplex haemolytic disease of horses
of great importance in the USA. The
disease is notifiable in the UK.
Immunity and epidemiology:
Animals can be virus-carriers for
several years despite having antibody.
Transmission is by the mechanical
transfer of leucocytes via mosquitoes,
flies, syringe-needles, semen and
milk.
Control:
UK. Horses can only be imported from
virus-free premises. However EIA is
widespread in damp areas of Germany
and Italy and so could enter the UK.
Summary of both lectures
• The retroviruses all contain RT and all
integrate and mutate, but do not cause acute
disease. This replication results in latency
and persistence and chronic diseases eg
tumours, immunosuppression and immune
complex disease.
• FeLV, but not FIV, is the most important
immunosuppressive viral diseases of cats in
the UK and suspect cats are blood tested for
antigen.
Summary of both lectures
(cont.)
• The viruses are labile and cell associated
and so close contact (eg in cat colonies or
winter –housed sheep), or sources of
leucocytes, eg blood, milk and semen,
transfer them
• Vaccines are not usual except to FeLV.
Summary of both lectures
(cont.)
• Visna maedi virus of sheep is endemic and
causes a T-cell based disease whereas EIA
is exotic and causes complement-mediated
haemolysis. Both involve bouts of variant
viruses and immune complex disease.
• The bovine viruses are of little importance
in the UK to date.