|
|
| (13 intermediate revisions by 3 users not shown) |
| Line 1: |
Line 1: |
| − | {{review}}
| + | #REDIRECT[[:Category:Tissue Cyst Forming Coccidia]] |
| − | | |
| − | {{toplink
| |
| − | |backcolour =
| |
| − | |linkpage =Parasites
| |
| − | |linktext =PARASITES
| |
| − | |pagetype=Bugs
| |
| − | |sublink1=Protozoa
| |
| − | |subtext1=PROTOZOA
| |
| − | }}
| |
| − | <br>
| |
| − | | |
| − | ==Neospora==
| |
| − | *2 main species
| |
| − | **''Neospora caninum'' in the dog
| |
| − | **''Neospora hughesi'' in the horse
| |
| − | | |
| − | *Sporulated oocysts measuring just 10μm
| |
| − | | |
| − | *Oocyst contains 2 sporocysts with 4 sporozoites
| |
| − | | |
| − | *Route of transmission not fully understood
| |
| − | | |
| − | *Often misdiagnosed as ''Toxoplasma gondii''
| |
| − | **''Sarcocystis'' cysts have thicker walls
| |
| − | | |
| − | *Infection diagnosed by IFAT, ELISA or PCR
| |
| − | **Identification of lesions and organisms in tissue using immunohistochemical staining
| |
| − | **Eliminate other causes of abortion first
| |
| − | | |
| − | '''Life cycle'''
| |
| − | *Life cycle similar to ''Toxoplasma gondii''
| |
| − | | |
| − | *Limited range of warm-blooded intermediate hosts
| |
| − | **Asexual reproduction occurs in intermediate host forming tissue cysts
| |
| − | | |
| − | *Host range of sexual stage is unknown for ''N.caninum''
| |
| − | **Intermediate host for ''N.hughesi'' is the horse, but the definitive host is unknown
| |
| − | | |
| − | *Final host
| |
| − | **Dogs pass oocysts
| |
| − | **Role not fully understood in pathogenesis
| |
| − | **5 day prepatent period
| |
| − | **Other wild canids may also act as final definitive hosts
| |
| − | | |
| − | *Intermediate host
| |
| − | **Mostly cattle
| |
| − | **Natural infection has been documented in other herbivores
| |
| − | | |
| − | *Transmission
| |
| − | **Transplacental infection occurs in all intermediate hosts and in the canine final host
| |
| − | ***Transplacental can occur in '''successive pregnancies'''
| |
| − | **In cattle, vertical transmission occurs
| |
| − | ***Post-natal infection occurs but is less common
| |
| − | | |
| − | '''Pathogenesis'''
| |
| − | *Dogs
| |
| − | **Occurs mainly in puppies
| |
| − | **Causes ascending paralysis, especially of hind limbs, with muscle wasting
| |
| − | **Causes sudden collapse due to myocarditis
| |
| − | **More than puppy in a litter may be affected, although this may not occur simultaneously
| |
| − | **Successive litters affected
| |
| − | | |
| − | *Cattle
| |
| − | **Commenest cause of infectious abortion in dairy cattle
| |
| − | **Congenitally infected calves can have encephalomyelitis and paresis
| |
| − | **Abortion usually occurs between 5-7 months of gestation but can occur as early as 3 months
| |
| − | **No other clinical signs in the cow
| |
| − | **Repeat abortions possible in same cow (persistently infected)
| |
| − | | |
| − | *Horses
| |
| − | **Myeloencephalitis
| |
| − | **Transplacental infection occurs
| |
| − | **Disease only diagnosed in USA
| |
| − | | |
| − | *''Neospora caninum'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
| |
| − | | |
| − | '''Prevention and Control'''
| |
| − | *Do not allow dogs access to calving cows, placental membranes and aborted or dead calves
| |
| − | | |
| − | *Do not allow dogs to defecate in cattle feeding areas
| |
| − | | |
| − | *Identify and cull seropositive cattle, or do not breed from them or their progeny
| |
| − | | |
| − | *Select seronegative cattle for breeding
| |
| − | | |
| − | *Vaccinate
| |
| − | **Only in the USA
| |
| − | **Neoguard or Intervet
| |
| − | **Killed protozoal vaccine for healthy, preganant cows
| |
| − | **Dosed in first 3 weeks of pregnancy and then every 3-4 weeks during gestation
| |
| − | **Revaccination with 2 doses during each subsequent pregnancy
| |
| − | | |
| − | ==Sarcocystis==
| |
| − | [[Image:Sarcocystis Life Cycle.jpg|thumb|right|150px|''Sarcocytis'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
| |
| − | [[Image:Sarcocystic.jpg|thumb|right|150px|''Sarcocytis'' - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]
| |
| − | *Most infections are asymptomatic
| |
| − | | |
| − | *Heavy infections are causes of chronic wasting in large animals, hide sondemnation and downgrading of carcasses
| |
| − | | |
| − | *''Sarcocystis'' should be differentiated from other tissue-cyst forming coccidia
| |
| − | | |
| − | *There are many species of ''Sarcocystis'' which differ in size from microscopic to several centimetres in length
| |
| − | **''S.neurona'' is an important equine pathogen in the USA
| |
| − | | |
| − | *Infective cyst in the intermediate host is called a '''sarcocyst'''
| |
| − | | |
| − | '''Life Cycle'''
| |
| − | *Individual life cycles incompletely misunderstood
| |
| − | | |
| − | *Indirect life cycle
| |
| − | | |
| − | *Life cycle alternates between the final and the obligatory intermediate host
| |
| − | | |
| − | *Only '''one''' final and '''one''' intermediate host
| |
| − | | |
| − | *Sporulated oocyst has 2 sporocysts containing 4 sporozoites
| |
| − | **Naked oocyst usually seen in faeces as the oocyst wall is very delicate
| |
| − | **Oocyst measures 15μm in length
| |
| − | | |
| − | *No schizogony in final host
| |
| − | | |
| − | *Gametogeny occurs deep in subepithelial tissue
| |
| − | | |
| − | *Faecal oocyst count is low
| |
| − | | |
| − | *Oocysts are sporulated when passed
| |
| − | **Difficult to find on faecal examination as the sporocysts are few in number and small
| |
| − | | |
| − | *Ingestion of sporocyst by intermediate host
| |
| − | **2 phases of rapid asexual reproduction in vascular endothelial cells
| |
| − | **Slow multiplication of bradyzoites in muscle tissue
| |
| − | **Sarcocyst forms with bradyzoites inside, surrounded by a cyst wall and divided into compartments
| |
| − | | |
| − | '''Epidemiology'''
| |
| − | *Final hosts are carnivores and omnivores
| |
| − | | |
| − | *Intermediate hosts are herbivores and omnivores
| |
| − | | |
| − | *Humans are the final host for some species and the intermediate hosts for others
| |
| − | **Final host for species infecting cattle and pigs
| |
| − | | |
| − | *Dogs are final hosts for species infecting cattle, sheep, goats, pigs and horses
| |
| − | | |
| − | *Cats are final hosts for species infecting cattle, sheep and pigs
| |
| − | | |
| − | '''Pathogenesis'''
| |
| − | *Widespread infection but mostly asymptomatic
| |
| − | | |
| − | *Cause meat inspection losses
| |
| − | | |
| − | *''Sarcocystis'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
| |
| − | | |
| − | *Experimental infections cause severe, acute pyrrhexic disease when the organism multiplies in the vascular endothelium
| |
| − | | |
| − | *Can cause chronic wasting disease in cattle and horses
| |
| − | **Causes abortion and post-natal disease in sheep
| |
| − | | |
| − | *Equine protozoal myeloencephalitis
| |
| − | **Necrotising encephalomyelitis affecting the grey and white matter of the CNS
| |
| − | **Caused by ''S.neurona''
| |
| − | **Opossum thought to be the definitive host
| |
| − | **Horses thought to be accidental hosts
| |
| − | **Natural intermediate hosts currently unknown
| |
| − | **Western Blotting shows 50% of horses in the USA are seropositive
| |
| − | **Risk factors poorly understood
| |
| − | **Causes spinal cord dysfunction
| |
| − | ***Ataxia and paralysis
| |
| − | | |
| − | ==Toxoplasma==
| |
| − | [[Image:Toxoplasma gondii.jpg|thumb|right|150px|''Toxoplasma gondii'' - Ke Hu and John Murray]] | |
| − | [[Image:Toxoplasma Life Cycle.jpg|thumb|right|150px|''Toxoplasma'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
| |
| − | *1 major pathogenic species called ''Toxoplasma gondii''
| |
| − | | |
| − | *Causes disease in a wide range of animal species including humans
| |
| − | | |
| − | *Important cause of abortion in sheep
| |
| − | | |
| − | *Zoonotic
| |
| − | **Can cause abortion
| |
| − | **Can cause congenitally aquired defects
| |
| − | | |
| − | *Forms a sporulated oocyst which is only 10μm
| |
| − | **Contains 2 sporocysts with 4 sporozoites
| |
| − | | |
| − | *Transmission through ingesting the intermediate host or via the faecal-oral route
| |
| − | | |
| − | '''Life Cycle'''
| |
| − | *Complex
| |
| − | | |
| − | *Usually indirect
| |
| − | **Reffered to as '''facultatively heterxenous'''
| |
| − | **Intermediate host is not essential for completion of the life cycle
| |
| − | | |
| − | *Gametogeny (sexual stage) is host specific for felids
| |
| − | | |
| − | *Any warm blooded animal can act as a facultative intermediate host
| |
| − | **Asexual reproduction occurs in the intermediate host forming tissue cysts
| |
| − | **Intermediate host swallows sporulated oocysts or tissue cysts
| |
| − | **Can be transferred between intermediate hosts by carnivorism
| |
| − | | |
| − | *Cats
| |
| − | **Sporulation occurs in 2-3 days
| |
| − | **Cats either swallow infective (sporulated) oocysts where ''Toxoplasma gondii'' as a prepatent period of 3 weeks
| |
| − | **Or eat the tissues of an infective intermediate host where ''Toxoplasma gondii'' as a prepatent period of 3-10 days
| |
| − | **Self-limiting infection
| |
| − | **Oocysts shed for 1-2 weeks
| |
| − | ***Shedding can occur later if immunity wanes or cat is immunocompromised
| |
| − | | |
| − | *Intermediate host
| |
| − | **3 sources of infection
| |
| − | ***Oocysts from environment contaminated by cat faeces
| |
| − | ***Eating cysts in tissues or other infected hosts through carnivorism or undercooked meat
| |
| − | ***Transplacental transmission in some host species during the acute phase of infection
| |
| − | | |
| − | *Acute phase of infection
| |
| − | **After infection of the intermediate host the organism undergoes a phase of rapid division and dissemination throughout the body
| |
| − | ***Parasite enters cell and asexual reproduction occurs by '''endogeny''' (budding) producing 8-16 '''tachyzoites'''
| |
| − | ***Tachyzoites are released when host cell bursts
| |
| − | ***Haematogenous spread as more cells are infected
| |
| − | ***Infection continues until the animal develops an immunity in 2 weeks when the infection enters the chronic phase
| |
| − | | |
| − | *Chronic phase of infection
| |
| − | **Occurs once the host's immune response has become effective
| |
| − | ***Groups of slow growing intracellular '''bradyzoites''' become walled off forming infective '''cysts'''
| |
| − | ***Bradyzoites inside cysts are protected from the host immune response whereas extracellular tachyzoites are killed
| |
| − | ***Cysts remain viable for months to years and are particulary numerous in muscle and nervous tissue
| |
| − | ***If immunity is suppressed the infection can revert to the acute form
| |
| − | | |
| − | '''Pathogenesis'''
| |
| − | *Cat
| |
| − | **In the intestinal phase of infection only the superficial cells at the tips of the villi are affected
| |
| − | **Little significant pathogenicity
| |
| − | | |
| − | *Sheep
| |
| − | **Mostly asymptomatic
| |
| − | **If a non-immune ewe is infected during pregnancy the consequences will be serious
| |
| − | ***Infection during the first trimester leads to resorbtion
| |
| − | **Infection during the second trimester leads to fetal death and mummification
| |
| − | **Infection during the last trimester leads to a weak or stillborn lamb
| |
| − | **Aborted ewes show focal necrotic placentitis with white lesions in the cotyledons and foetal tissue
| |
| − | **Diagnosis is confirmed by Giemsa and serology of the ewe's blood
| |
| − | | |
| − | *Clinical outbreaks of toxoplasmosis are '''sporadic'''
| |
| − | **Immunity is aquired before tupping
| |
| − | **Significant ill-effects are unlikely if immune ewes are infected during pregnancy
| |
| − | **Not shed from sheep to sheep so predicting outbreaks is difficult
| |
| − | | |
| − | *Humans
| |
| − | **Mostly asymptomatic
| |
| − | **Virulent strains cause flu-like symptoms, malaise and/or lymphadenopathy
| |
| − | **In immunodeficient patients, disease can be caused by even avirulent strains
| |
| − | **If a non-immune women is infected during pregnancy, abortion or the birth of a congenitally infected child can result
| |
| − | ***E.g. Hydrocephalus, opthalmitis, mental retardation
| |
| − | | |
| − | *Dogs
| |
| − | **Complication of canine distemper
| |
| − | **Causes [[Respiratory Parasitic Infections - Pathology#Toxoplasmosis|pneumonia]] and encephalitis
| |
| − | | |
| − | *Cattle and horses
| |
| − | **Sometimes infectious causing opthalmitis
| |
| − | | |
| − | *Toxoplasma can cause [[Pancreas Inflammatory - Pathology#Acute haemorrhagic pancreatitis|acute interstitial pancreatitis]] in systemic toxoplasmosis
| |
| − | | |
| − | *''Toxoplasma gondii'' causes [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
| |
| − | | |
| − | '''Epidemiology'''
| |
| − | *Serology
| |
| − | **Sabin-Feldman Dye test (old method)
| |
| − | **ELISA
| |
| − | **Mouse innoculation for confirmation
| |
| − | | |
| − | *Cat
| |
| − | **30-80% test seropositive
| |
| − | **Each cat sheds oocysts for 1-2 weeks of its life
| |
| − | | |
| − | *Human
| |
| − | **30% seropositive in UK, 70% seropositive in France
| |
| − | | |
| − | *Meat animals
| |
| − | **Significant proportion of cattle, sheep, pigs and rabbits can tissue cysts
| |
| − | | |
| − | '''Prevention'''
| |
| − | *Cat
| |
| − | **Impossible if cat is allowed outdoors (will hunt!)
| |
| − | **If kept indoors, only canned food should be fed and vermin controlled
| |
| − | **ELISA to check if seropositive
| |
| − | | |
| − | *Human
| |
| − | **Avoid oocyst ingestion
| |
| − | ***Wash potentially contaminated raw food thoroughly
| |
| − | ***Wash hands after gardening or handling cats and especially before eating
| |
| − | ***Clean out cat litter trays every day before oocysts sporulate
| |
| − | **Avoid ingestion of tissue cysts
| |
| − | ***Do not eat undercooked meat
| |
| − | ***Wash hands after eating raw meat
| |
| − | ***Take care when lambing or dealing with sheep abortions and stillbirths
| |
| − | ***Pregnant women should avoid lambing altogether when pregnant
| |
| − | | |
| − | *Sheep
| |
| − | **Toxovax vaccine
| |
| − | ***Live, avirulent strain of ''Toxoplasma''
| |
| − | ***Does not form bradyzoites or tissue cysts
| |
| − | ***Killed by host immune system
| |
| − | ***Single dose given 6 weeks before tupping
| |
| − | ***Protects for 2 years
| |
| − | ***Immunity boosted by natural challenge
| |
| − | **Medicated feed can be given daily during the main risk period
| |
| − | ***14 weeks before lambing
| |
| − | **The best method of protection is to prevent cats from contaminating the pasture, lambing sheds and feed stores
| |