Urogenital Parasites - Toxo + Neo

Toxoplasma gondii and Neospora

Toxoplasma gondii

protozoa - apicomplexa phylum

infects most warm blooded animals and all tissues with them

causes toxoplasmosis - forms cysts

Facultatively heteroxenous (can use multiple hosts)

Toxoplasma gondii lifecycle OVERVIEW of host variation

Cat = definitive host

MAIN LIFECYCLE - successful due to complexity

• prepatent period: oocyst = ~ 3 wks; tissue cyst: 3-10 days

(cats can be directly infected by ingesting faecal oocyst they produce → self limiting for 1-2wks)

OR cat ingest infected rodents or birds (common intermediate hosts - cat natural prey) that contain tissue cysts

OTHER INTERMEDIATE HOSTS

• affects a range of livestock - SHEEP + PIGS produce tissue cysts

• humans can ingest sheep/pig tissue cysts and therefore become infected

• or human infected DIRECTLY from cat

  • ingest oocyst from contaminated cat faeces:

  • 1) from contaminated water or fruit

  • 2) not washing hands after cleaning cat litter tray

• or human to human transmission

  • 1) transplacental infection (mother→ foetus)

  • 2) from infected organ transplant

  • 3) latent infection → once infected & immunocomprimised

T. gondii - Lifecycle in cat more detail

1) infected cat produces oocyst

2) unsporulated oocyst shed from cat

3) oocyst sporulates in the env (2-3 days)

4) oocyst becomes sporulated with sporozoites [2 sporocysts containing 4 sporozoites 2×4)

5) sporulated oocyst enters the intermediate host

• contamination of birds and rodents via soil and water

6) 8-16 tachyzoites → killed within 2 weeks killed by immune system = acute phase

7) but by that stage already converted into bradyzoites which form tissue cysts in muscle or nervous tissue = chronic phase

8) IH = rodent or bird - eaten by cat

9) cat infected and cycle continues

Neospora caninum

intro

definitive host - dogs

main intermediate host of relevance - cows - abortion risk

Phylum Apicomplexa, subgrouo coccidia

• Coccidia group:

  • cyst forming = toxo and neo

  • non-cyst-forming = eimeria

N. caninum life cycle - Horizontal Transmission

• Dog shed unsporulated oocyst [definitive host = canids]

  • dogs - UK, Coyote + Dogs - USA

  • foxes are not - so no sylvatic cycle in the UK

• contaminates environment

• sporogony occurs - 2 (cytes) x 4 (zoites)

• Ingestion of Sporulated Oocyst by Intermediate Host

  • usually cattle (others = goats and sheep)

  • Cattle ingest oocysts from contaminated feed, water, or pasture

• Excystation: In the small intestinal enzymes break down oocysts to release 8 sporozoites (infective stage).

• Migration to Tissues: Sporozoites invade enterocytes, enter the bloodstream, and spread to tissues (muscles, brain, placenta).

• Tissue Cyst Formation: Sporozoites become tachyzoites (rapidly dividing via endo-dyo-geny) and later form bradyzoites (encysted form) in tissues.

  • Endodyogeny = two daughter tachyzoites inside the mother cell - mother cell bursts open

  Canids eat infected tissue of IH/cow

  • same as toxoplasm

• Bradyzoites → Trophozoites → schizonts

• → Schizogony [asexual]: schizonts → merozoites)

• Gametogony [sexual] : meroziotes form macro and microgamtes

• Sporogony: shed unsporulated oocysts in faecesthat sporulate in the env.

N. caninum life cycle - Vertical Transmission

2 instances of vertical transmission when:

• when sporozoites invade the placenta and form tachyzoites (that replicate via endodyogeny)

  • Final host: bitch → puppies}

  • Intermediate: cow → calf

Pregnant cows, Neospora can be transmitted to the fetus via the placenta, causing abortion or stillbirth.

• Clinical Signs: Infected cows may show reproductive issues, but many are asymptomatic. Chronic infection can affect the nervous system.

Zoonotic? Toxo vs Neo

Toxo - yes

Neo - no

Difference btw Toxo and Neo tissue cysts

Toxo - thinner cyst wall

Neo - thicker cyst wall (cows are bigger than rodents)

However - they are antigenically distinct (different serological tests)

Toxo vs Neo - which one has wider host range?

Toxo

Localisation of tissue cysts - Toxo

Mostly muscle and heart

(some in CNS)

Localisation of tissue cysts - Neo

Mainly CNS
A few in the muscle and heart

Patent period definition

period of acute infection when the parasite is reproductively active and producing detectable life stages

Presence → detection via diagnostic tests (when tachyzoites are present)

Prepatent definition

The prepatent period is the time between when a parasite enters the host and when it becomes detectable

time host entry → detection (usually in faeces)

Toxo final host - patency and prepatency (x2)

Tissue cyst prepatency [when next see oocysts in faeces]

• 3-10 days

Oocyst prepatency [when next see oocysts in faeces]

• ~3 wks

Patency [when tachyziotes detectable]

• 1-2 weeks

Neo final host - patency and prepatency (x1)

Tissue cyst prepatency [when next see oocysts in faeces]

• 5 days

• dogs less likely to reinfect themselves compared to toxo

  • due to very low prevalence of oocyst shedding in dogs

  • seroprevalence > oocyst shedding

  • dogs can act as intermediates host as well as the final host

  • therefore can have tissue cyts without shedding oocysts

Patency [when tachyziotes detectable]

• 2-3 weeks - could reach 4 months

Canine neosporosis

• Pups more likely to have disease than older dogs (immunocomprimised)

• uneven distribution of infection within a litter → vertical transmision varies between litter mates

• Neo - tissue infection primarily CNS → clincial signs = paralysis and muscle wasting

• occasional myocarditis - occasionally tissue cysts in myocardium

• Limited natural immune protection

Neo Caninum DIRECT diagnosis

Serology, Histopatholoy, PCR

other methods

• immunohistology

• cell culture

• can infect animal from samples - possible but not used

Bovine Neospora

Significant cause of abortion in dairy cattle

Coinfections may exacerbate

Repeated abortions likely - due to limited natural immune response

Otherwise asymptomatic unlike in final host - link to CNS

Variable seroprevalence in herds

At what point does abortion occur over resorption in bovine neosporosis?

5+ months = abortion

(remember 9 month pregnancy)

What are the different kinds of bovine neosporosis vertical transmission?

1) Exogenous

• cow mothers are infected from dog sporulated oocyst

• epidemic-like abortion seen on farm - up to 50% abortion rate

• only one wave - not persistently infected

• so

2) Endogenous

• calf born after transplacental infection

• REMAINS PERSISTENTLY INFECTED

• calf grows up with chronic-persistent infection

• higher risk of abortion (permanent abortion episodes) - 2-7 higher

• immune system doesn’t recogise infection

• well below average reproductive success on farm

• Neospora irregularly infects foetuses

• Both routes have potential to produce non-infected calves from infected mothers

Neo vs Toxo - prevalence of vertical transmission

Neo

• repeated infections after mother gets infected

• all future offspring at risk

• and then infected offspring CAN vertically transmit neosporosis

Toxo

• ONCE - usually when primary infection when pregnant

• latent infections usually leaves foetus alone

• infected offspring do not vertically pass on unless primary infection occurs

N. caninum Ab detection

Samples from serum, single or tank milk sources

ELISA
Immunofluorescence

Immunoblot - gel electrphoresis and then use immunofluorescence

Neo Dog prevention

Limit access to cows, their placentas, their abortions and dead calves

Feed processed (dry/tinned food) rather than raw

Neo cattle prevention

Cull or do not breed (select seronegative for breeding) infected cattle + progeny - females

Prevent dogs defaecating near cattle

US vaccinations

• Neoguard → killed vaccine, weak immune response so many boosters

Toxo cat pathogenesis

• final host

• limited pathogenicity

• superficial cells (eneterocytes) of villi

Sheep Toxo - When does foetal death and reabsorption occur?

ewe primary infection @ 0-40 days/147

Sheep Toxo - When does foetal death and abortion/mummification occur?

ewe primary infection @ 40-110days/147

Sheep Toxo - when do stillborn or weak lambs occur?

ewe primary infection @ 110-147

Sheep Toxo Pathogenesis

bradyzoites appear as white foci of necrosis on cotyledons of the placenta

(strawberry lesions)

How do bradyziotes cause Toxoplasma abortions in sheep

• disrupt blood flow to foetus - containing nutrients and oxygen

• disrupts waste removal from foetus

• disrupts progesterone production and maintenance of endometrium lining

• invasion of immune cells causes inflammation

Immunocompetent human Toxo postnatal infection

mostly asymptomatic

life long persistence of infection

will have tissue cysts but will not be aware of them

Immunocompromised human Toxo postnatal infection

Can be highly lethal

flu-like symptoms, cerebral or opthalmic disorders

Reactivation of toxoplasmosis in immunodeficiency

• can cause cerebral manifestations (brain lesions, fever, dizziness, headaches), necrosis and CNS abscesses

Primary or reactivated Human Prenatal infection (foetus)

• cerebral necrosis

• opthalmic disorders

• hydrocephalus

• death

Cat epidemiology - Toxo

seropositive > patent (acute infection) oocyst excreting cats

• because infection eventually becomes latent

• higher levels of toxoplasma at cat latrines

• majority of cats are infected

Toxo oocyst - environmentally resistant

can remain in soil greater than a year

but vulnerable to heat

• destroyed in 10 mins when food cooked

Meat epidemiology

Lowest risk of tissue cyst ingestion - cattle

Mid - horse and intensively farmed chicken

High risk - pigs, goats, sheep and free-range chickens + others

• many seropositive sheep - key disease causing sheep abortions

Human Toxo epidemiology

approx 1 in 3 people are seropositive in UK
750 cases of prenatal (foetal) cases a year

France - very high prevalence (80%)

Epidemiology Overview - insert pi

Toxo diagnosis (4 methods)

1) Giemsa - stains free zoites and cysts

2) ELIZA

3) PCR

4) Agglutination

Serology for Toxo

IgM high → primary immune response

IgG high → secondary immune response

Cat Toxo prevention

control impossible outdoors

Indoors

• diet control → restrict to processed food

• no vermin

Human Prevention

Oocysts

• cook food - wash raw food

• wash hands when cleaning litter tray and clean them daily

Tissue cysts

• cook meat

• wash hands after handling raw meat

• wear gloves around lambing/sheep/abortions/stillbirths

Sheep Prevention (primarily preventing abortions)

Vaccinate - ToxoVac

• live - Tachyzoites that have lost ability to form bradyzoites/cysts

• susceptible hist immunity

• <2 years protection - decent length as live vacciation

• minimise exposure to cat faeces

Lamb medication put in their feed to for Toxo

De-co-quin-ate

Decoquinate

Neospora hughesi

Horse intermediate host

definitive host unknown

Restricted to US

Causes myeloencephalitis (CNS inflammation)in horses

Related to sarcocystis neurona → CVRS protozoa group

Neospora hughesi lifecycle

unsporulated oocyst → sporogony/sporulation→ enters horse (intermedate host→ [sporzoites converted to tachyzoites] → endodyogeny → bradyzoites and cyst formation → unknown final host eats tissue cyst