Clinical Pathology - Lecture 9

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Veterinary Parasitology

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- The science that deals with the parasites of domestic animals

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Parasite

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- May be defined as a two-species association.

▪Which one species, the parasite, lives on or in a second species, the host, for a significant period of its life and obtains nourishment from it

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Macroparasites

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- Multicellular, readily multiply within the host, have a long generation time (weeks to months), and feature chronic infections

•Microorganisms such as bacteria and viruses are also considered parasites

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Parasites

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- An extremely varied group

- Ranges from species such as flies, fleas and ticks to roundworms(nematodes) such as the heartworms and hookworms.

- Endoparasites

- Ectoparasites

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Endoparasites

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- internal parasites , where the mature stage or sexual stage is present within the body of the host.

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Ectoparasites

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- External parasites that attach to the skin and body openings of the hosts organisms.

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Phylum Arthropoda (arthropods)

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- Invertebrate animals, such as insects and arachnids, that have a segmented body, paired jointed appendages, and usually a chitinous exoskeleton

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▪Subphylum Crustacea

•Class Insecta

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- Order Siphonaptera

•Family Pulicidae

▪Ctenocephalides spp.

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▪Subphylum Crustacea

•Class Insecta

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- Order Diptera

•Family Oestridae (bot flies)

▪Gastrophilus spp.

• Family Tabanidae (horse and deer flies)

▪Tabanus spp.

▪ Chrysops spp.

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•Phylum Arthropoda

▪Subphylum Chelicerata

- Class Arachnida (Subclass: Acari)

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- Order Parasitiformes [Suborder Ixodida (= Metastigmata)]

•Family Ixodidae (hard ticks)

▪Amblyomma americanum (lone star tick)

▪Dermacentor spp. (dog tick)

▪Ixodes scapularis (deer tick)

•Family Argasidae (soft ticks)

▪Otobius megnini

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•Phylum Arthropoda

▪Subphylum Chelicerata

- Class Arachnida (Subclass: Acari)

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- Order Sarcoptiformes

•Family Sarcoptidae

▪Sarcoptes scabiei

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•Phylum Arthropoda

▪Subphylum Chelicerata

- Class Arachnida (Subclass: Acari)

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- Order Trombidiformes

•Family Demodicidae

▪Demodex spp

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Parasites within each major group share similar what?

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- Morphologic, Physiologic, and Reproductive features

•Each feature a set of well-defined and recognizable life cycle stages unique to their group

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Definitive Host

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- Host which harbors the adult, mature, or sexual stage of a parasite

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Intermediate (biological) Host

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- The host, which is required, harbors a developing larval, immature, or asexual stage of a parasite

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Paratenic (mechanical) Host

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- Host where no parasite development or infection occurs

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Larvae

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- An immature, intermediate stage of development of a parasite

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Life cycle

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- The development of the parasite, tracking it through the various phases of its life history; life cycle patterns can be quite simple or very complex

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Ovum

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- An egg

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Zoonotic

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- A disease which can be spread from animals to humans

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Vector

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- A parasite which transfers disease (usually bacterial or viral) from one animal to another

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Life Cycle

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- The development of the parasite from adulthood, through any intermediate stages, into sexual maturity and into egg production

- The intermediate stages may involve one or more intermediate hosts ( a host which is required to harbor a developing larval, immature, or asexual stage of a parasite)

▪ In some cases, dogs, cats, or domestic animals ARE the intermediate hosts

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Young parasites

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- Always complete some part of their development somewhere other than on its definitive host

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Most internal parasites complete their life-cycle by doing what?

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- Depositing their eggs in the feces of the host animal

▪Examination of host feces for parasitic ova (eggs) generally establishes the diagnosis

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Diagnosis of external parasites generally involves:

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- Direct observation of the adult or immature parasite on the host animal

- Observation of “signs of infestation” on the host animal

- Observation of characteristic lesions and clinical signs in the host animal

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Flea

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Fleas

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- Small (1 - 5 mm), brown to black, wingless, laterally compressed insects

- Reside in the hair coats of mammals, including the dog and cat

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Flea development stages

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- Egg. larva, Pupa and Adult

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How do fleas attach to the skin of a host?

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- By their peircing mouthparts

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What do fleas do before they feed on blood?

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- They inject saliva to prevent clotting

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What does a flea have that helps them make long jumps?

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- Long bristley legs

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How far can a flea jump?

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- Over 300 mm horizontally

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Two most significant flea species in dogs and cats:

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- Ctenocephalides canis (the dog flea)

- Ctenocephalides fenis (the cat flea)

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Ctenocephalides canis

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- Infects the dog and cat

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Ctenocephalides fenis

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- It is the most frequent flea affecting both dogs and cats

•It also infects many different hosts worldwide including ferrets, racoons, opossums, wild canids, and when necessary, humans

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The fleas mouth has two functions

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- Squirting saliva or partly digested blood into the bite

- Sucking up blood from the host 》This process can mechanically transmits pathogens that may cause disease

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When fleas smell exhaled carbon dioxide from humans and animals what do they do?

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- They jump rapidly to the source to feed!!

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Wingless fleas

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- Cannot fly, but it can jump long distances with the help of small powerful legs

•A flea can use its legs to jump up to 200 times its own body length

•It can also jump about 130 times its own height

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How big is a fleas body?

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- About one tenth of an inch

• Constructed to make it easier to jump long distances

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The fleas body consists for three regions:

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1. Head

2. Thorax

3. Abdomen

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The fleas head and the thorax have rows of bristles which are called what?

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Combs

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The fleas abdomen consists of how many segments?

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- Eight visible segments

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Flea ovoid (eggs)

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- 0.5 mm long

- White eggs are laid on host

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Flea eggs can fall on what type of surfaces?

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- Carpet

- Floor

- Soil

- Lawn

- Etc..

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What type of temperature do the flea eggs need to be in?

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- Warm temperature and humidity (moderate to high) is right

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How many days do white, legless, worm-like larvae usually hatch from eggs?

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10 days

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Larvae move under what type of surfaces?

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- soil surface or organic material outside and into carpets and cracks in the floor inside

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What do flea larvae feed on and how many days does it take for them to produce?

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- They Feed on adult flea feces and in 5 - 12 days they produce a silk-like cocoon in which they pupate (the cocoon is sticky, attracting bits of debris

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How many days does it take for adult fleas to emerge?

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- Adults emerge, depending upon conditions, in 5 to 140 days

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Where do the flea adults move to and home many days do they last?

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- They move to the host where they reside for their entire life which lasts up to 100 days

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The Fleas life cycle

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- Usually completed in 3-4 weeks

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When do fleas mate and what do they do after?

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Fleas mate after feeding and begin egg production within 48 hours of taking their first blood meal

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Fleas are susceptible to what kinds of temperatures?

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- Cold and the various stages do not survive the North temperate winter outside

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Primary clinical feature

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Pruritis (itching)

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Pruritis

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- Secondary to inflammation caused by irritation from the flea saliva

- Host skin is generally reddened (erythema) and features raised papules

- Repeated scratching often leads to secondary bacterial skin infection (pyoderma) and crusting

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As fleas consume quantities of blood, this ingested blood is excreted as?

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- Reddish-black fecal pellets or long tubular coils on the animal’s hair and skin

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Excreted blood is referred to as...

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- "flea dirt"

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Fleas can consume relatively large amounts of blood which can cause:

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- Heavy flea infestations》 blood loss and anemia (flea anemia), particularly in puppies and kittens

- Prolonged blood loss》 (iron-deficiency anemia)

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Flea Allergy Dermatitis (FAD)

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- Hypersensitivity occurring in some animals associated with flea bites

- Involves an overreaction of the body’s immune system (hypersensitivity) to the flea saliva causing a much more severe clinical syndrome

- Most frequent skin disease of dogs and is also an important disease of cats

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In both dogs and cats, the most severely affected areas are those where most fleas locate and feed:

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- The back near the base of the tail

- Inner thighs

- Ventral abdomen

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FAD Signs depend upon the extent of exposure and the degree of sensitivity

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- Intense pruritus, restlessness and discomfort

- Scratching, biting and rubbing exacerbates the dermatitis

- May have areas of alopecia, scaling, hyperpigmentation, and thick, leathery skin = lichenification

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Uncontrolled FAD = Pyoderma

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- In cats, the numerous small, papulocrusting lesions are referred to as miliary dermatitis

》Often found affecting areas around the neck and tail-head

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What can fleas transmit?

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Tapeworm》 Dipylidium caninum

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Tapeworm eggs are ingested by who in what type of environment

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- Ingested by the flea's larval stages when feeding in the pet's environment

- The eggs develop into a dormant life stage within the developing flea

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What will happen if the flea is ingested by the animal while grooming?

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- he tapeworm is released and continues to develop into the adult worm within the intestine of the animal

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The Black Death (Bubonic Plague)

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- One of the worst natural disasters in history

- Caused by the bacteria Yersinia pestis

- Spread throughout Asia, Europe, and Africa (killed 75 – 200 million people overall)

》Killed one third of the population of Europe in 1347 - 1350

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What was the primary culprits in transmitting The Black Death (Bubonic Plague) disease?

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- Oriental Rat Fleas carried on the back of black rats

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What happened to the fleas when the bacteria multiplied inside of them?

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- Bacteria blocked the flea's stomach causing it to be very hungry

- Flea would then start voraciously biting a host and continued to feed in a frenzy

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What was happening when the diseased fleas kept biting the host?

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- Infected blood carrying the plague bacteria, flowed into the human's wound

- The plague bacteria now had a new host and the flea soon starved to death

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Corticosteroids

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- Used topically and systemically in the palliative treatment of FAD

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Chlorinated hydrocarbon and organophosphates

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- Occasionally used

- Potential toxicity compounds》should be used with caution

- Some compounds used topically in dogs and cats over six months of age

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Botanically derived compounds

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- Synthetic pyrethrins