Hookworms and filaria nematodes Flashcards
Hookworms and filaria are classified as which parasite type?
Nematodes
Name the two common hookworms of dogs and cats
- Uncinaria stenocephala
- Ancylostoma spp
Describe the main features and morphology of Uncinaria stenocephala
- Found in dogs and foxes
- 1cm long
- Found in the SI
- Typical hooked appearance
- Large buccal capsule with 2 cutting plates
- Seen in the UK
Describe the main features and morphology of Ancylostoma caninum
- Found in dogs and foxes
- 1cm long
- Found in the SI
- Typical hooked appearance
- Large buccal capsule with teeth
- Tropics, subtropics, Europe, USA
How are Uncinaria stenocephala and Ancylostoma caninum differentiated from their morphology?
Uncinaria has a buccal capsule with cutting plates
Ancylostoma has a buccal capsule with teeth
Describe the life cycle of Uncinaria stenocephala
Egg –> infective L3 = 4-8 days in environment
Primary route of infection – ingestion of L3
No migration
Within gut L3-L5 development
How long is the PPP for Uncinaria stenocephala?
15 days
Describe the percutaneous infection of Uncinaria stenocephala
The L3 invade in through the skin into the muscle, but the host immune response kills these L3, so they don’t have the opportunity to reach the gut and continue to develop
Describe the life cycle of Ancylostoma caninum
Egg –> infective L3 = 5-8 days in environment, temperatures > 15C
4 possible ROI
How long is the PPP for Ancylostoma caninum?
15 days
Describe the 4 routes on infection of Ancylostoma caninum
- Ingestion of L3, no migration, L3-L5 within the gut
- Percutaneous: L3 migrate via lymphatic system & bloodstream to lungs (L3-L4). Coughed up and swallowed -> small intestine L4-L5
- Ingestion of L3 that penetrate buccal mucosa and migrate following the same method as the percutaneous route
- Transmammary via milk: L3 remain dormant in subcutaneous tissues until pregnancy. Swallowed, small intestine L4-L5
Describe the disease associated with Uncinaria stenocephala
Not highly pathogenic:
- Protein losing enteropathy, (anaemia)
- Weight loss, lethargy
- Diarrhoea
Describe the disease associated with Ancylostoma caninum
Highly pathogenic:
• Voracious blood suckers (0.1ml blood per worm per day)
• Severe anaemia in puppies
• Lassitude, under weight, poor condition
•+/- diarrhoea
Typical in dogs less than 1 year old
How are hookworms diagnosed?
Diagnosis based on identification of typical strongyle eggs in faeces plus clinical signs
History of the dog: Imported dog/has the dog travelled
Compare the size of Uncinaria eggs and Ancylostoma eggs
Uncinaria = 70-90um Ancylostoma = 50-80um
How are hookworms treated?
Susceptible to most anthelmintics:
- Benzimidazoles
- Macrocyclic lactones
- Ivermectin is toxic in dogs and must not be prescribed
What are the general features of filarial nematodes
- Generally large (2-50cm)
- Eggs larvate in utero or L1 are born live
- Use invertebrates as intermediate host
- Adults may parasitize tissues other than GI tract
What is the name of the filarial nematode termed the ‘heartworm’?
Dirofilaria immitis
How is Dirofilaria immitis transmitted?
Mosquitos
Describe the life cycle of Dirofilaria immitis up to moulting into adults
- Mosquito takes a blood meal and deposits L3 into the dogs skin which migrate through the puncture wound left behind
- The L3 moult into L4 in the dermis (3 days post infection)
- Over the following weeks the L4 migrate through the tissues of the dog
- At day 50-70 post infection the L4 larvae moult into immature adults
Describe the left cycle of Dirofilaria once they are adults
- The immature adults migrate into the venous blood stream, transporting them towards the heart and lungs
- By day 120 they worms have all arrived in the small pulmonary blood vessels (1-1.5 inches in length)
- They then grow larger and larger, migrating into larger pulmonary BVs until some finally end up in the pulmonary artery
What are the effects of Dirofilaria immitis in the CV system?
- An inflammatory response within and around the pulmonary vessel is elicited by the parasite, ultimately resulting in vascular resistance and pulmonary hypertension
- With higher worm burdens, right sided hypertrophy of the heart develops leading to right sided HF
- Also responsible for a marked increase in thromboembolisms
How do mosquitos become infected with Dirofilaria immitis?
7-9 months post infection, the adult, sexually mature, female worms start to produce offspring (microfilaria), these circulate in the CV system of the dog ready to be ingested by a mosquito
Describe the life cycle of Dirofilaria immitis in the mosquito
Inside the insect, over a period of about 14 days, the L1 larvae develop into the infective L3 stage causing this mosquito to now be a vector
How does Dirofilaria immitis affect cats?
- Cats are relatively resistant to infection
- Infections consist of less worms
- Often does result in a patent infection
How large can Dirofilaria worms grow?
L5: 2-4cm
Adults: Females = 30cm, males = 20cm
What are the clinical signs of Dirofilaria immitis throughout infection?
- Asymptomatic in the early stages of disease
- Disease associated with adult worms
- Mild persistent cough and dyspnea
- Reluctance to exercise and fatigue after moderate activity
- Decreased appetite and weight loss.
- Right-sided congestive heart failure
What signs are associated with right sided congestive HF?
Ascites, abdominal swelling, anorexia, death.
Which diagnostic test for Dirofilaria immitis detects microfilariae?
Knott test
What are some other diagnostic tests for Dirofilaria immitis?
- Antigen test detects adult ovarian antigens
- Radiography and echocardiography
Describe prophylactic treatment for Dirofilaria immitis
Macrocyclic lactones (selamectin, moxidectin, or milbemycin)
- Once monthly for 60 days
- Kill microfilariae, L3 and early L4 stages of heartworm
- Typically lasts a month
Describe treatment for Dirofilaria immitis
- Macrofilaricidal (adult worms) – only dogs
- Doxycycline
- Melarsomine: only approved macrofilaricide, 3 dose regimen (60, 90 and 91 days)
What is the name of the ‘oriental eyeworm’?
Thelazia callipaeda
What are the features of Thelazia callipaeda
- Vector borne zoonotic nematode
- Transmitted by fruit flies
- Adult parasites found in the eye and associated tissues (conjunctiva)
- Ulceration, conjunctivitis
- Treat with moxidectin
What is the most significant disease associated with Uncinaria?
Pedal dermatitis associated with repeated exposure to L3.
What types of dogs is Uncinaria most frequently seen?
Dogs kept outside on earth runs, e.g. farm dogs, hunt hounds, working dogs and those kept under poor husbandry conditions.
What are the classical clinical signs of heartworm infection?
Low worm burdens manifest as exercise intolerance, soft cough, weight loss, fainting (lypothymia).
Heavier worm burdens can lead to congestive heart failure.
