VM 607 - Parasitology (Infectious Disease)

define obligate parasite

- Can only exist as a parasite inside a host

define facultative parasite

capable of living either free or have a parasitic existence

define endoparasite

parasite that lives within the body of the host

define ectoparasite

a parasite that lives on the outside of the body of the host infestation

define spurious parasites

false infection - an organism or egg found on fecal examination that is from a source outside of the individual and is not related to an infection of the individual being examined

how do organisms often pick up "spurious parasites"

often derived from eating part of a host infected with a parasite

define zoonotic parasites

parasites that typically infect animals but have ability to infect humans

define host

organism that harbors and nourishes the parasite

define host-specific parasites

can only infect and cause disease in a particular host(s)

define definitive host

host in which parasite undergoes sexual reproduction

define intermediate host

no sexual reproduction of parasite occurs in intermediate host, but parasite can propagate by binary fission

define paratenic/transfer host

atypical (substitute) intermediate host that ingests and harbors the infective parasite stage which remains active and unchanged (collector or storage host)

What happens if a suitable host ingests a paratenic host or part of it containing an infective parasite?

parasite can undergo its usual development and cause disease in the suitable host

define vector host

an organism (often arthropod) that carries a parasite from host to host - parasite can undergo sexual reproduction and binary fission in vector host

define reservoir host

host in which parasite lives and develops but does not cause disease & is available for transmission to another host

modes of parasite transmission

- free living stage ingested by host (passive transmission)

- free living stage penetrates host (active transmission)

- infected intermediate host ingested by definitive host

- vector transmission

general categories of parasites

1. protista

2. nematoda (roundworms)

3. platyhelminths (flatworms)

4. arthropoda (insects)

define protozoa

unicellular eukaryotes classified based on morphology & means of locomotion

examples of protozoa

- trichomonas, trypanosoma, giardia, babesia, leishmania

protozoa are ____ celled

single

Platyhelminths (flatworms) are _______

a. multicellular

b. unicellular

a. multicellular

types of flatworms

1. tapeworms (cestodes)

2. flukes (trematodes)

nematodes are also known as _______worms

roundworms

Roundworms are.....?

a. free-living

b. parasitic

c. both

c. both

most nematodes are ______ (can be male and female in one)

dimorphic

difference between male and female roundworms

males are smaller than females and have a bent tail for holding the female for copulation

what are acanthocephala

Thorny-headed worms

what are examples of arthropods

insects = mosquitoes, lice, fleas

arachnids = ticks and mites

What are the direct effects of parasites?

Feeding and destroying tissues, production of toxins, mechanical interference

What are the indirect effects of parasites?

Host allergic responses, secondary infections, effect on competition & predation

T/F: The effects of a parasite are always size-related.

False - not necessarily related to size

Often, the worst effects of parasites may be found when the parasite is in the wrong _____ or _____

host, site

what are the effects of a narrow host specificity

limits distribution, improves probability of synchronization of parasite & host life cycles

benefits of a host specific parasite

if a parasite only infects certain species, can be easy to control (host finding)

trypanosomes overview

protozoan parasites classified under genus Trypanosoma - can cause serious disease in animals and humans

life stages of trypanosomes

Amastigote

Promastigote

Epimastigote

Trypomastigote

amastigote

round, no external flagellum, intracellular form within host cells (in Leishmania and T. cruzi)

promastigote

kinetoplast is at the anterior end with the flagellum, the extracellular form of Leishmania injected into vertebrae host by insect vector

Epimastigote

kinetoplast is located between anterior end and nucleus (juxtanuclear) with a short undulating membrane running from the middle to the anterior end - extracellular form of other trypanosomes in the insect vector

trypomastigote

kinetoplast posterior to nucleus and the flagellum arising near it to run along a long undulating membrane the length of parasite - bloodstream extracellular stage

african trypanosomes of veterinary importance

trypanosoma brucei, trypanosoma congolense, trypanosoma vivax

Trypanosoma brucei - who does it affect, how is it transmitted, and what is the reservoir?

- african trypanosome transmitted by Tsetse flies

- causes debilitating disease in livestock and humans

- wildlife (buffalo) are reservoirs

Trypanosoma congolense - who does it affect, how is it transmitted, and what is the reservoir?

- african trypanosome transmitted by Tsetse flies

- causes disease in livestock, particularly cattle

- wildlife are reservoirs

Trypanosoma vivax - who does it affect, how is it transmitted?

- livestock trypanosome found in South America & Africa

- transmitted by tsetse flies and hematophagous dipterans

clinical signs of african trypanosomes

- anemia, intermittent fever, edema, chronic wasting, swollen lymph nodes, death

diagnosis of african trypanosomes

- dried thick & thin blood smears during febrile stage stained w/ Giemsa

- dried thin & thick smears from neddle biopsies of prescapular and precrural LNs

- serological (ELISA) tests; PCR

treatment for African trypanosomes

Diminazene aceturate, melarsomine dichlorhydrate, Suramin, Isometamidium chloride.

controls for african trypanosomes

vector elimination using insecticide-treated traps

leishmania characteristics

- intracellular protozoan parasites

- transmitted by sand flies

- causes leishmaniasis (disease affects humans, dogs, and other animals)

Leishmania exists as _______ in the sand fly and ________ in the host's cells, specifically in macrophages.

promastigotes in the sand fly

amastigotes in host cells

which leishmania species cause visceral leishmaniasis?

L. donovani and L. infantum

which leishmania species cause cutaneous leishmaniasis?

L. tropica, L. major, L. braziliensis

Dogs are primarily commonly infected with L. _______

L. infantum/L. chagasi

Infection w/ L. infantum is endemic among what brreds in North America?

foxhounds

clinical signs of visceral leishmania in dogs and humans

initial skin lesion with an incubation period of weeks to months --> leaads to remittent low-grade fever, malasia, pancytopenia, hypergammaglobulinemia, hepato- and splenomegaly, cachexia, bleeding disorders, chronic illness, death

diagnosis of visceral leishmaniasis

- clinical signs and history of travel to endemic areas

- serology and PCR tests

Definitive diagnosis depends on finding the parasite in:

▪ Biopsy, histology, or culture of spleen, liver, bone marrow or lymph nodes

▪ Postmortem examination of RES tissue

▪ Blood smears or blood culture

Diagnosis of Cutaneous & Mucocutaneous Leishmaniasis

▪ Clinical Signs and History of travel to endemic area

▪ Serology

Definitive diagnosis requires finding parasites in:

➢ Biopsy of skin lesion, tissue taken from border of ulcer

➢ Culture of biopsy

➢ Giemsa stain or smear of ulcer scraping

T/F: Leishmaniasis in dogs is less resistant to treatment than in humans.

False - more resistant

What drugs are commonly used in the treatment of leishmaniasis in dogs?

Pentavalent antimonials and allopurinol

Is improvement guaranteed after treatment for leishmaniasis in dogs?

No, relapses are common.

What is the dosage of allopurinol used for maintenance therapy in dogs with leishmaniasis?

10 mg/kg

What are the benefits of maintenance therapy with allopurinol in dogs with leishmaniasis?

Decreases parasitemia, maintains infected dogs in an asymptomatic state, and decreases the likelihood of direct or vector transmission.

What is a method of leishmania control in endemic areas?

Vector control and elimination of stray dogs; use of insecticide-treated dog collars.

What is a method of preventing leishmaniasis in non-endemic areas?

Euthanasia of infected dogs prevents leishmaniasis from becoming endemic.

T/F: Leishmania is a zoonotic disease.

True

importance of leishmania in the USA

- Leishmaniasis is considered zoonotic, meaning it can spread from animals to humans

- There have been outbreaks among foxhounds in the U.S. and Canada, with some evidence of direct dog-to-dog transmission. The absence of sand fly vectors in these areas suggests other transmission methods, like biting or breeding, are involved.

babesia characteristics

- intraerythrocytic hemoprotozoa

- pyriform, round, or oval shaped

- causes disease called babesiosis

- worldwide distribution

- zoonotic parasite

How is babesiosis transmitted?

by tick bite

- brown dog tick (primary), american dog tick (secondary)

also can be iatrogenic transmission = via blood transfusion or blood-contaminated fomites

definitive and intermediate hosts for babesia

two primary hosts: a tick (definitive host) and a mammalian host (intermediate host)

What initiates the life cycle of Babesia in canines and bovines?

Transmission by ticks when an infected tick bites a mammalian host and introduces Babesia sporozoites into the bloodstream.

What happens during asexual reproduction of Babesia in the mammalian host?

Sporozoites invade red blood cells, transforming into trophozoites that undergo binary fission, producing merozoites.

What occurs when infected red blood cells rupture in the Babesia life cycle?

The rupture releases merozoites into the bloodstream, infecting new red blood cells and causing symptoms like anemia, fever, and jaundice.

What happens when a tick feeds on an infected mammal in the Babesia life cycle?

The tick ingests red blood cells containing Babesia merozoites.

What occurs inside the tick after it ingests Babesia merozoites?

The parasite undergoes further development and sexual reproduction in the tick's gut, resulting in zygotes that migrate to the salivary glands.

What is the final stage of Babesia development in the tick before it infects a new host?

The zygotes develop into motile forms that become sporozoites, ready to infect a new mammalian host during the tick's next blood meal.

What is the pre-patent period for canine babesiosis?

1 to 3 weeks

What type of anemia is associated with canine babesiosis?

Moderate to severe hemolytic anemia

What are common clinical signs of canine babesiosis?

Fever, anorexia, depression, pallor, splenomegaly, and bounding pulse

what two babesia species affect cattle

babesia bovis and babesia bigemina

babesia bigemina clinical signs

anorexia, high fever, anemia, and jaundice

babesia bovis clinical signs

infections often more severe w/ potential neurological effects due to brain capillary sequestration

- leads to symptoms like incoordination and involuntary leg movements

T/F: Most babesia-infected animals showing CNS signs die.

True

babesia diagnosis methods

- blood smears (thick or thin and stained with Giemsa) can reveal babesia piroplasms within RBCs

- serological tests like IFA or PCR testing

- can inoculate patient blood into very susceptible species like guinea pigs and hamsters (wtf)

babesia canis piroplasms

larger and often found in pairs

babesia gibsoni piroplasms

small, pleiomorphic, ring-shaped organisms

treatment for babesia canis

- treated w/ imidocarb diproprionate

treatment for babesia gibsoni and babesia conradae

combined therapy with atovaquone and azithromycin

T/F: Treatment for babesiosis eliminates all disease.

False - treatment reduces parasitemia and clinical signs, but infection may not be eliminated and infected dogs remain as carriers

treatment for bovine babesiosis

- diminazene aceturate or imidocarb injections - treatment in cattle much more effective than in dogs

how to prevent/control babesiosis

- tick control through acaricides in livestock, esp. in high-risk areas

- screen blood donors to prevent iatrogenic transmission

- avoid splenectomy or corticosteroid injections of babesia + dogs

- no dog fighting! = avoid mechanical transmission

characteristic features of cytauxzoon felis

- intra-erythrocytic apicomplexan protozoan

- reservoir hosts = bobcats

T/F: Cytauxzoon felis is extremely pathogenic in domestic felines.

True

What is the vector for cytuaxzoon felis?

primarily by ticks - american dog tick

What happens when an infected tick bites a cat?

It introduces sporozoites (infective stage) into the cat's bloodstream.

What do sporozoites infect once inside a cat?

They infect macrophages and undergo asexual reproduction.

What do sporozoites form within macrophages?

They form schizonts that dramatically enlarge the cells.

What happens after schizonts mature in a cat?

They release merozoites into the bloodstream.

What can merozoites infect in a cat?

They can infect red blood cells (RBCs), forming piroplasms.

What occurs when a tick feeds on an infected cat?

It ingests piroplasms and the parasite undergoes sexual reproduction.

Where does the parasite travel after sexual reproduction in the tick?

It travels to the salivary glands, ready to infect another feline host.