Parasitology and Physiology

Define the terms:

• Endotherm

• Ectotherm

• Homeotherm

• Poikilotherm

Endotherm: an animal that generates their own body heat through internal metabolic processes

Ectotherm: an animal that relies on external environmental sources to heat their body

Homeotherm: an animal that maintains a stable, constant internal body temperature within a narrow range, regardless of the surrounding environment

Poikilotherm: an animal whose internal body temperature changes and varies depending on the surrounding environment

Define the terms:

• Thermoneutral zone

• Lower and upper critical temperatures

• Zone of thermal comfort

• Thermal setpoint

Thermoneutral zone: the range of ambient environmental temperatures where an organism maintains its core body temperature using basic dry heat loss mechanisms without changing metabolic heat production

Lower and upper critical temperatures: minimum and maximum temperatures of the thermoneutral zone

Zone of thermal comfort: the range of temperatures resulting in psychological thermal satisfaction

Thermal setpoint: the target core body temperature value

Describe the process of conduction in heat exchange

• Heat transfers through direct physical contact between particles

• Fast-vibrating particles collide with neighbouring particles, passing kinetic energy along

Describe the process of convection in heat exchange

• Heat transfers through the movement of fluids, which includes both liquids and gases

• Warm fluid expands and rises, while cooler fluid sinks to replace it- creating a circulating current

Describe the process of radiation in heat exchange

• Heat transfers via electromagnetic waves through space, without needing any medium or contact

• Objects emit infrared waves that travel outward until they strike another object and warm it

Describe the process of evaporation in heat exchange

• Heat transfers away from a surface as a liquid changes state into a gas

• High-energy liquid molecules escape into the air as vapour, leaving cooler molecules behind

Describe the Q10 effect

Metabolic rate increases for every 10℃- this is the Q10 effect

• A Q10 value of 2 means that metabolic rate doubles for every 10℃

• A Q10 value of 3 means that metabolic rate triples for every 10℃

Give the equation linking M, CD, C, R and E- including what is represented by these letters

M: metabolic rate 

CD: conduction

C: convection 

R: radiation

E: evaporation 

Hs = Hm - (∓Hcd ∓Hc ∓Hr - He)

Describe the action of the thermoregulatory centre, including its location

The thermoregulatory centre is located in the hypothalamus, specifically within the preoptic area

• The centre uses a negative feedback mechanism to constantly balance heat gain and heat loss

• Temperature receptors monitor the temperature of blood flowing through the brain 

• Receptors in the skin detect external changes and send nerve impulses to the hypothalamus

• If the core temperature strays from the normal set point, the centre sends electrical impulses to effectors (muscles, sweat glands, blood vessels) to correct it

List the physiological mechanisms used by endotherms against low temperatures

• Vasoconstriction

• Shivering: involuntary rapid muscle contraction

• Non-shivering thermogenesis: brown adipose tissue breaks down fats to release heat

• Piloerection: erector muscles pull hair/feathers up to trap an insulating layer of warm air 

• Hormonal regulation: thyroxine increases the basal metabolic rate to produce more internal heat

• Decreased sweating: prevents evaporative cooling

List the behavioural mechanisms used by endotherms against low temperatures

• Huddling: reduces exposed surface area and shares body heat between animals

• Increased activity: moving around generates friction and muscular heat

• Torpor/hibernation: metabolic rate/body temperature is lowered to conserve energy

• Seasonal changes in fat/fur: allows for better insulation

List the physiological mechanisms used by endotherms against high temperatures

• Vasodilation

• Sweating: absorbs body heat through evaporation

• Panting: increases water evaporation from the respiratory surfaces of the mouth/lungs

• Gular fluttering: rapidly vibrating membranes of the throat and floor of the mouth to increase evaporative cooling

• Thermal windows: highly vascularised appendages are designed to radiate excess heat

List the behavioural mechanisms used by endotherms against high temperatures

• Habitat selection: seeking shade, burrowing underground or entering water to avoid direct solar radiation

• Stretching out: increases surface area exposed to moving air 

• Shifting to nocturnal or crepuscular activity to avoid the hottest parts of the day

• Licking the fur/skin: utilises the cooling effect of moisture evaporation

• Urohidrosis: excreting urine onto the legs so the evaporating liquid cools blood vessels in the limbs

Give the lower critical temperature range of:

• Naked human

• Newborn lamb (wet)

• Newborn lamb (dry)

• Newborn piglet

• 100kg pig

• Arctic fox

• Dairy cow producing 30L milk/day

Naked human- 28 to 29

Newborn lamb (wet)- 38 to 40

Newborn lamb (dry)- 25 to 30

Newborn piglet- 34 to 35

100kg pig- 0 to 5

Arctic fox- -40 to -70

Dairy cow producing 30L milk/day- -15 to -30

What happens during the last few weeks of pregnancy in ewes to help the lamb survive for the first few hours?

In the final weeks of pregnancy, brown fat is laid around the heart and kidneys to act as an energy source

Describe how you can recognise the different severities of hypothermia in lambs

• Normal temperature: 39-40℃

• Mild-moderate hypothermia: 37-39℃

  • Hunched posture, lowered head

  • Hollow flanks 

  • Lethargy

  • Excessive bleating

• Severe hypothermia: <37℃

  • Inability to hold the head up

  • Lying flat out and unresponsive

How could you manage hypothermia in lambs under five hours old?

1. Towel dry

2. Place in a warming box or under a heat lamp until temperature rises above 37℃

3. Give 50ml/kg warmed colostrum via stomach tube

4. Continual gradual warming to 39℃ before returning the lamb to the ewe

How could you manage hypothermia in lambs over five hours old?

1. Administer an intraperitoneal injection of warm 20% glucose solution (10ml/kg) into the abdomen, before attempting to warm or feed

2. Towel drug

3. Place in a warming box or under a heat lamp until temperature rises above 37℃

4. Give 50ml/kg warmed colostrum via stomach tube

5. Continual gradual warming to 39℃ before returning the lamb to the ewe

In which clinical scenarios (aside from hyperthermia) might you lower the body temperature of an animal?

• Cardiac arrest: neuroprotection

• Status epilepticus: neuroprotection

• Acute spinal cord injury: minimises swelling

• Cardiac and vascular surgeries: restricts blood flow to specific areas

• Topical anaesthesia: numbs peripheral nerve endings

When might Bair Huggers be used?

FAM (forced air warming) systems such as Bair Huggers are often used to treat perioperative hypothermia, affecting up to 80% of anaesthetised cats and dogs

Define the terms:

• Tidal volume

• Inspiratory reserve volume

• Expiratory reserve volume

Tidal volume (Vₜ): the amount of air inhaled or exhaled during one normal, quiet respiratory cycle

Inspiratory reserve volume (IRV): the extra volume of air that can be maximally inhaled after a normal tidal inhalation

Expiratory reserve volume (ERV): the extra volume of air that can be maximally exhaled after a normal tidal inhalation

Define the terms:

• Residual volume

• Inspiratory capacity

• Viral capacity

Residual volume (RV): the volume of air remaining in the lungs after maximal forced expiration, preventing lung collapse

Inspiratory capacity (IC): the maximum amount of air that can be inspired following a normal tidal expiration 

Vital capacity (VC): the maximum volume of air that can be exhaled after a maximal inhalation

Define the terms:

• Functional residual capacity

• Total lung capacity

• Respiratory rate

Functional residual capacity (FRC): the amount of air remaining in the lungs at the end of a normal tidal expiration

Total lung capacity (TLC): the absolute maximum volume of air the lungs can hold after a maximal inspiratory effort

Respiratory rate (f): the number of breaths taken per minute

Define the terms:

• Minute ventilation

• Dead space

• Alveolar exchange

Minute ventilation (Vₑ): the total volume of air inspired or expired per minute

Dead space (V_d): the volume of the respiratory tract that does not participate in gas exchange

Alveolar ventilation (Vₐ): the volume of air per minute that reaches the alveoli and takes place in gas exchange 

Give the equation for inspiratory capacity

Inspiratory capacity (IC) = Tidal volume (Vₜ) + Inspiratory reserve volume (IRV)

Give the equation for vital capacity

Vital capacity (VC) = Tidal volume (Vₜ) + Inspiratory reserve volume (IRV) + Expiratory reserve volume (ERV)

Give the equation for functional residual capacity

Functional residual capacity (FRC) = Expiratory reserve volume (ERV) + Residual volume (RV)

Give the equation for total lung capacity

Total lung capacity (TLC) = Vital capacity (VC) + Residual volume (RV)

Give the equation for minute ventilation

Minute ventilation (Vₑ) = Tidal volume (Vₜ) x Respiratory rate (f)

Give the equation for alveolar ventilation

Alveolar ventilation (Vₐ) = (Tidal volume (Vₜ) - Dead space (V_d)) x Respiratory rate (f)

Draw a diagram to show:

• Inspiratory reserve volume

• Tidal volume

• Expiratory reserve volume

• Residual volume

• Inspiratory capacity

• Functional residual capacity

• Vital capacity

• Residual volume

• Total lung capacity

When does a ventilation/perfusion mismatch occur?

A V/Q mismatch occurs when the normal ratio of air entering the alveoli (V) to the blood flow in the capillaries (Q) is disrupted

What is a high V/Q mismatch? What is it caused by?

• Ventilation exceeds perfusion, meaning there is airflow to an area of the lung, but blood flow through the capillaries is reduced/blocked

• Causes: pulmonary embolism, pulmonary hypertension, decreased cardiac output

What is a low V/Q mismatch? What is it caused by?

• Perfusion exceeds ventilation, meaning blood flows through the capillaries but the matching alveoli receive little to no air 

• Causes: chronic obstructive pulmonary disease, pneumonia, atelectasis, acute respiratory distress syndrome, pulmonary fibrosis

List the two endoparasite groups of veterinary importance

Nemathelminths (threadworms)

• Nematoda (roundworms)

Platyhelminths (flatworms)

• Cestoda (tapeworms)

• Trematoda (flukes)

Describe 3 examples of canine respiratory parasites

• Nematodes (lungworms): Angiostrongylus vasorum, Crenosoma vulpis, Eucoleus aerophilus

  • Infects the airways and lung tissue

  • Transmitted by ingesting infected slugs/snails

• Lung flukes: Paragonimus sp.

  • Forms cysts inside the lung tissue

  • Transmitted by ingesting raw/undercooked intermediate hosts (crayfish, crabs, rodents)

• Nasal mites: Pneumonyssoides caninum

  • Live inside the nasal passages and sinuses

  • Transmitted by nose-to-nose contact with another infected animal

Describe 3 examples of canine cardiac parasites

• Nematodes (lungworms): Angiostrongylus vasorum

  • Also known as French Heartworm 

  • Adults live in the heart and pulmonary arteries 

  • Transmitted by ingesting infected slugs/snails

• Heartworm: Dirofilaria immitis

  • Live in the pulmonary arteries and the right side of the heart 

  • Transmitted by mosquito bites

• Parasitic kinetoplastid: Trypanosoma cruzi

  • Attacks the heart muscle

  • A protozoan parasite carried by ‘kissing bugs’

Define the terms:

• Parasitism

• Mutualism

• Commensalism

Parasitism: only one organism benefits from the interaction, at a detriment to the other

Mutualism: organisms of different species both benefit from the interaction

Commensalism: only one organism benefits from the interaction, without causing any harm to the other

Define the terms:

• Facultative parasite

• Obligate parasite

• Endoparasite

• Ectoparasite

Facultative: may survive in the absence of the host 

Obligate: at some or all stages of the life cycle cannot survive in the absence of the host

Endoparasite: lives internally inside the host 

Ectoparasite: lives in/on the outer body surfaces of the host

Define the terms:

• Definitive host

• Intermediate host

• Permissive host

• Non-permissive host

• Reservoir host

• Paratenic host

• Vector (include both types)

Definitive: the host in which parasite sexual reproduction occurs 

Intermediate: the host in which parasite asexual reproduction occurs 

Permissive: not usually used by the parasite, but still favours life cycle completion

Non-permissive: the host in which the parasite cannot complete the life cycle

Reservoir: temporary host used in the absence of the natural host

Paratenic: will host the parasite without any further development

Vectors:

• Mechanical: a vector which mechanically spreads the parasite, and is not utilised in the life cycle

• Biological: a vector needed by the parasite to complete part of the life cycle

How can parasites be transmitted?

Food

Water

Soil

Direct contact

Airborne

Vector-borne

Mother-to-fetus

What is the difference between a direct and indirect parasite life cycle?

Direct life cycle: parasitic stages develop in/on one host

Indirect life cycle: intermediate host(s) is needed for the development of some stages of the parasite

What kind of information should you know about the life cycle of a parasite?

1. What is the type of life cycle?

2. Who serves as a definitive host?

3. Who serves as an intermediate host (if any)?

4. What is the infective stage?

5. What is the route of infection?

Why is it useful to study the parasite life cycle?

• Determine an appropriate therapeutic window 

• Manage disease properly

• Protect other animals from cross-infection

• Protect the public from zoonotic infections

How can you control the spread of parasites?

Bovine lungworm is the only vaccine-preventable parasitic disease

Hygiene

Nutrition

Disruption of transmission

Describe the 3 different ways of detecting parasites

Microscopic

• Coproscopic faecal samples using Baermann’s larval migration assay

• Cytological profile of bronchoalveolar lavage fluid 

Serological

• Antigen-based assays

• Antibody-based assays

Molecular

• Conventional PCR: inhibitors in faeces can limit sensitivity

• Real-time PCR: for detection of infection in definitive and intermediate hosts, and can detect DNA circulating in canine blood

How can you differentiate between nematode sp.?

Size differences

Species specificity

Morphological differences

Describe the life cycle of dipylidium caninum

1. Infected adult flea is ingested

2. Adult worms develop in the small intestine

3. Posterior segments of the adult worms are passed in the faeces

4. Segments and egg packets are found in faeces and on fur 

5. Eggs are ingested by larvae flea

6. Larvae flea develops into an adult flea, and contains an immature tapeworm

Describe the life cycle of fasciola hepatica

1. Metacercaeriae cysts in grass are ingested

2. Fluke develops into an adult within the host

3. Eggs are passed in faeces

4. Miracidium larvae form 

5. Intermediate snail host

6. Cercaeriae develops into Metacercaeriae cysts in grass 

Describe the life cycle of d.viviparus

1. Host ingests L3 whilst grazing on contaminated pasture

2. L3 larvae leave their protective sheath, and pierce the wall of the host’s intestine

3. Larvae move to the local lymph nodes and molt into L4

4. They travel through the lymphatic system and blood vessels to the heart and lungs

5. Once in the alveoli/bronchioles, they break through into the airways and molt into L5

6. L5 move into the trachea and bronchi, where they grow into full adults

7. Females lay eggs containing L1, which are passed through the digestive tract and into the environment via faeces

8. Once outside, L1 molt twice in warm, damp weather to become infective L3 larvae in 5-7 days

Describe the life cycle of angiostrongylus vasorum

1. A dog/fox becomes infected by ingesting an infected slug or snail, containing L3 

2. The L3 larvae burrow through the intestinal wall and travel to nearby lymph nodes, where they molt into L4 and L5

3. The L5 travel to the pulmonary arteries and the right side of the heart, where they grow into adult worms and lay eggs 

4. The eggs move to the lung capillaries, where they hatch into L1

5. L1 break through the alveolar walls, move into the digestive tract and exit the body through faeces

6. Once in the environment, L1 is either eaten by a snail/slug, or will actively penetrate the foot

7. Inside, they grow and molt twice- until they reach the infective L3 stage 

Describe the life cycle of aelurostrongylus abstrusus

1. Cat becomes infected by eating an infected paratenic host

2. The L3 larvae burrow through the intestinal wall and travel to nearby lymph nodes

3. They travel via the lymphatic/circulatory system to the lungs, where they develop into adults

4. Adult worms live in the terminal respiratory bronchioles and alveolar ducts 

5. Female worms lay eggs in the lung parenchyma, which hatch into L1

6. L1 break through the alveolar walls, move into the digestive tract and exit the body through faeces

7. Once in the environment, L1 is either eaten by a snail/slug, or will actively penetrate the foot

8. Inside, they grow and molt twice- until they reach the infective L3 stage 

Describe the life cycle of ascaris suum

1. Pigs ingest eggs containing L3 from contaminated soil, food or water

2. The larvae hatch inside the small intestine, and penetrate the intestinal wall

3. Larvae travel to the liver, where they burrow through tissue leaving fibrous scars (milk spots)

4. The blood carries larvae to the heart and lung capillaries, where they break through the alveolar walls, and move into the digestive tract

5. Back in the small intestine, they undergo molts to become L4 and L5

6. By 6 weeks, they reach adulthood and live in the lumen of the small intestine 

7. Females produce eggs, which are passed via faeces into the environment

8. Fertilized eggs develop into L3 in the soil within 3-4 weeks under warm, moist conditions

Describe the life cycle of toxocara Canis

1. A puppy is infected by ingesting eggs from contaminated soil/objects

2. Eggs hatch in the small intestine, and larvae pierce the gut wall

3. Larvae travel via the blood stream to the heart and lungs

4. The blood carries larvae to the heart and lung capillaries, where they break through the alveolar walls, and move into the digestive tract

5. Back in the small intestine, they undergo molts to become L4 and L5

6. By 6 weeks, they reach adulthood and live in the lumen of the small intestine 

7. Females produce eggs, which are passed via faeces into the environment

8. Environmental development takes 2-6 weeks, where the eggs embryonate and become infectious

Describe the different types of arthropod

Pentastoma: tongue worms

Insecta: diptera (flies), phthiraptera (lice), siphonaptera (fleas)

• Lice can either be biting (mallophaga) or sucking (anoplura)

Arachnida: astigmata (mites), prostigmata (mites), mesostigmata (mites), metastigmata (ticks)

• Ticks can either be hard (ixodidae) or soft (argasidae)

How do diptera affect animals?

Lucilia sericata- green bottle/blow fly

• Attracted by dirty wool due to scouring or foot rot wounds

Fly strike

• Eggs are deposited on skin

• Larvae lacerate skin and burrow 

• This is a distressing condition, and may be fatal due to secondary infection/septicaemia

Describe the pulmonary parasites that commonly affect ruminants and equids

Dictyocaulus sp.

• D.viviparus (cattle, deer and camelids)

• D.filaria (sheep and goats)

• D.arnfledi (donkeys and horses)

Adult lungworms live in the trachea and bronchi, causing parasitic bronchitis (‘husk’)

Deposition of eggs or newly hatched larvae may lead to parasitic pneumonia

The male has a copulatory bursa

How can you detect d.viviparus?

• Baermann apparatus is used to detect L1 larvae in faeces

• ELISA testing 

• Postmortem of lungs

• Histopathology

Describe the differences between mild, moderate and severe infection of d.viviparus

Clinical Sign	Mild Infection	Moderate Infection	Severe Infection
Coughing	Intermittent, more pronounced on exercise	Frequent even at rest	Deep, harsh cough
Respiratory rate	Often normal (30 bpm)	Tachpnoea (40-60 bpm)	Severe tachypnea (>80 bpm)
Lung auscultation	Often normal, some occasional squeaks	Pronounced squeaks and crackles	Pronounced squeaks and crackles
Other signs	None	Usually none	Dyspnoea, salivation, fever

Why has cattle lungworm increased?

Increased reliance on anthelmintics instead of vaccination comprises the build-up of immunological responses

Survival of L3 on pasture may have improved due to climatic change

Describe the clinical signs of d.arnfieldi

• Persistent cough

• Not responding to certain drugs 

• Lung sounds on auscultation

How does d.arnfieldi differ between donkeys and horses?

Donkeys

• Infection has a pre-patent period of 13 weeks

• Adult parasites are found in small bronchi 

• Patent infection with eggs in faeces

Horses

• Horses are most likely infected when kept on pasture with donkeys 

• Not patent, very few (if any) eggs in faeces

How can you diagnose d.arnfieldi?

A bronchoalveolar lavage or a tracheal wash may reveal worms, and larger numbers of eosinophils

Which pulmonary parasites commonly affect dogs?

• Angiostrongylus vasorum

• Oslerus osleri 

• Eucoleus aerophilus

• Filaroides sp.

• Crenosoma vulpis

Which pulmonary parasites affect cats?

Aelurostrongylus abstrusus

Which pulmonary parasites affect sheep and goats?

• Muellerius capillaris 

• Protostrongylus rufescens

Which pulmonary parasites affect swine?

Metastrongylus apri

What is the type of life cycle of angiostrongylus vasorum?

Life cycle is indirect

• Dog is the definitive host

• Slug/snail is the intermediate host

What do the antigens of angiostrongylus vasorum cause?

• Type III hypersensitivity (immune complex deposition)

• Complement activation

• Immune infiltrate in lungs and other tissues

What does L1 of angiostrongylus vasorum cause?

• Pulmonary inflammation/granuloma

• Pulmonary arteriolar vasoconstriction

How can you detect angiostrongylus vasorum?

• Radiography (interstitial pulmonary patterning, right ventricular/atrial enlargement

• Detection of L1 in faeces

• Detection of L1 in BAL fluid

How can you treat angiostrongylus vasorum?

• Fenbendazole

• Moxidectin

• Milbemycin

What is the type of life cycle of aelurostrongylus abstrusus?

Life cycle is indirect

• Cat is the definitive host

• Slug/snail/rodent/bird is the intermediate host

How can you detect aelurostrongylus abstrusus?

• Radiography (bronchiointerstitial patterning)

• Detection of L1 in faeces

• Detection of L1 in BAL fluid

How can you treat aelurostrongylus abstrusus?

• Fenbendazole

• Ivermectin

• Levamisole

What are nontrue lungworms?

Nontrue lungworms only have a lung phase during their migration 

The residing tissue for adults is not the lungs (commonly the intestine)

How does toxocara Canis affect all types of dog?

• In older/adult dogs, larvae bypass the lungs and undergo somatic migration- spreading through the blood stream to go dormant in skeletal muscles and organs

• In pregnant females, the dormant larvae ‘wake up’ due to hormonal shifts in the final trimester

• Puppies can be infected through the mother’s milk

What are the different types of larva migrans?

Visceral larva migrans: migration through organs 

Ocular larva migrans: migration through the eye

Cutaneous larva migrans: migration through the skin

Describe how the different species of dilofilaria affect different animals

• Dogs/cats (cardiac/pulmonary): D.immitis

• Dogs/cats (ocular): D.repens

• Raccoon (subcutaneous): D.tenius

• Bear (subcutaneous): D.ursi

• Porcupine (subcutaneous): D.subdermata

Describe the factors affecting d.immitis distribution

Maturation of microfilariae to infective L3 requires 2 weeks at 27℃, and the temperature should not be below 14℃

Mosquito breeding on water (all juvenile stages are aquatic)

Mosquito species which support the microfilariae

The presence of susceptible hosts

Describe the life cycle of d.immitis

1. A mosquito carrying L3 bites a dog and deposits the larvae onto the skin, where they actively enter through the wound into the body

2. Within 3 days, L3 molt into L4 in the skin and connective/muscle tissues 

3. Over the next 2 months, L4 larvae migrate to the pulmonary arteries and the right side of the heart, where they undergo their final molt 

4. Over several months in the pulmonary vessels, they grow significantly and release microfilariae into the bloodstream

5. A mosquito bites the infected dog, and ingests the circulating microfilariae 

6. Inside the mosquito’s Malpighian tubes, the microfilariae molt twice, progressing to L3

7. The L3 larvae migrate to the mouthparts (proboscis), ready to infect a new dog

Describe how cardiopulmonary disease can progress following d.immitis

Narrowing of pulmonary artery

• Disruption of intima leads to platelet influx and production of platelet-derived growth factor (PDGF), which increases proliferation of medial smooth muscle cells and fibroblasts

Exercise intolerance 

Hydrothorax

Hydroperitoneum 

Chronic cough

Dyspnoea

Haemoptysis

Eosinophilia in lung 

Oedema in lung parenchyma

Describe the roles of different immune cells in parasitism

Eosinophils: important in parasitic and allergic diseases (migrate from the blood into the tissue)

• Eosinophilia occurs in blood and tracheal washes during cardiorespiratory parasitism 

Basophils: degranulate at the surface of blood-borne parasites (microfilariae)

Mast cells: the tissue version of basophils- activate and produce amines, such as histamine

Histamine: an important vasodilator, which increases the number of immune cells in tissues

Neutrophils: D.immitis carries Wolbachia, which plays a role in neutrophil-induced inflammation seen in heartworm infection

Describe the roles of:

• Large granules

• Small granules

• Cytokines

In parasitism

Large specific granules

• Major basic protein

• Eosinophil cationic protein

• Eosinophil derived neurotoxin

• Eosinophil peroxidase

Small granules

• Aryl sulfate 

• Acid phosphatase

• Gelatinase

Cytokines

• IL3, IL5 (eosinophil growth factors)

• IL1, IL6, IL8, TNF-Alpha

Describe caval syndrome

Large worm burden in the right atrium and posterior vena cava

Increased venous pressure damages liver parenchyma

Increased cholesterol content of erythrocyte membranes, leading to fragility and haemolysis

Severe anaemia may be seen in blood as erythrocytes are replaced 

Erythrocyte haemolysis leads to haemoglobinaemia, bilirubinaemia, haemoglobinuria and jaundice

Describe how you can diagnose heart worm

Complete blood count (CBC)

• Some other diseases will give similar results

Knotts test/Millipore filter (acidic phosphatase staining or methylene blue) to enrich the microfilariae

• Microfilariae may not be seen if few are present

• Occult infections are not detected

Thoracic radiographs

• Some other diseases will give similar results

Electrocardiogram/echocardiogram (double line= heartworm)

• Difficult to interpret

Arteriogram

Indirect fluorescent antibody 

ELISA 

• Only adult female uterine antigens are detected

• False negatives occur if immature females are present, there is a male-only infection, or if there is an issue with the kit

Tracheal wash

What is shown?

Heartworm

How would you treat:

• Adult heartworm

• Microfilariae

Adult worms

• Melarsomine dihydrochloride (ImmiticideⓇ)

Microfilariae

• Ivermectin (HeartguardⓇ)

• Milbemycin (InterceptorⓇ)

• Both can be used as preventative for prophylaxis

Describe the use of adulticides in heart worm infection

Dead worms may induce significant inflammatory immune reactions

This can lead to pulmonary thromboembolism (clot in the pulmonary artery, blocking blood flow)

Disseminated intravascular coagulation (DIC)- microcoagulation, high platelet counts, endothelial damage

With increased activity, blood flow to the blocked vessels will increase, and cause capillary rupture- further increasing pulmonary vascular resistance and right-sided heart failure

Draw a table to show the differences between feline and canine heart worm

Feature	Feline Heartworm	Canine Heartworm
Susceptibility	60%	80-100%
Worm lifespan	2-3 years	5-7 years
Number of worms	1-6	Can be >30
Ectopic infection	Common	Uncommon
Microfilaraemia	1 month (<20%)	Persistent (80-90%)
Organ pathology	Lung	Heart and lung

What are the complications in diagnosing feline d.immitis?

Usually amicrofilaraemia, therefore blood smears may give false negatives

Diagnosis may be improved by analysing blood samples acquired in the evening, when parasites are more active (nocturnal periodicity)

A clinically infected cat may give very low worm burdens- therefore ELISA analysis to detect the antigen may give false negatives

Single-sex infections occur more in cats: no microfilariae may be produced

Describe how ELISA can be used to diagnose feline heart worm

In cats, very few worms can cause significant pathology

ELISA which detects the antigen (used in dogs) may not be sensitive enough 

The ELISA developed for use in cats instead measured antibody to parasite (rather than parasite antigen)

1. Antigen is attached to well

2. Test sample is added

3. Labelled antibody which detects feline IgG is added

4. Substrate is added

5. Colour develops, result is read on a plate reader

Describe the limitations of using ELISA to diagnose feline heart worm

• Positive antibody results may not tell you the current status, since the antibody can be present in cats who have previously be infected

• Although antibody titre can be raised in ongoing infection, it is difficult to correlate antibody titre with worm burden or current/previous infection 

• It is a less appropriate screening test, and should interpreted in relation to clinical signs and other diagnostic findings

What is the main function of the cardiovascular system?

The function of the cardiovascular system is to deliver oxygenated blood to the tissues, and remove carbon dioxide

What is reflected by oxygenation of arterial blood in the tissue?

Oxygenation of arterial blood in the tissue reflects blood pressure, heart function, breathing and lung function

How can you measure oxygen delivery?

To measure tissue oxygen delivery, we can measure: tissue perfusion and blood-oxygen content

What is tissue perfusion driven by?

Tissue perfusion is driven by mean arterial blood pressure (MAP)

How can MAP be measured?

• Invasive measurement

• Non-invasive measurement

• Feeling the pulse (very difficult)

Invasive measurement

• Gives real-time pressure

• Gives more information from a trace 

• More accurate 

• Insert a cannula into a peripheral artery

• Connect cannula to transducer

• Reported as systolic/diastolic (mean)

Non-invasive measurement

• Sphygmomanometry

• Oscillometric 

• Doppler

Describe what CVP (central venous pressure) measures, and give the normal values

CVP measures the pressure of blood returning to the right side of the heart

This reflects the volume of blood returning 

Normal values

• Cats: 0-5cm water

• Dogs: 0-10cm water

• To convert from mmHg to cm water, multiply by 1.36

How can you measure cardiac output? What is cardiac output?

Rarely used

Can use Fick method, dye, thermodilution, bioimpedance, pulse contour analysis, lithium

Cardiac output is the product of stroke volume (SV) and heart rate (HR)