Ectoparasites in Small Animals. Life Cycles

PRESENTATION

BROCHURE

LIFE CYCLES OF ECTOPARASITES Dunbar Gram Jeanmarie Short Heather D. Stockdale Walden

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Ectoparasites in Small Animals.

Life Cycles k eBoo

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LIFE CYCLES ECTOPARASITES Dunbar Gram Jeanmarie Short Heather D. Stockdale Walden

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Small handbook gathering all the life cycles of the most common ectoparasites in dogs and cats. Similar parasites are grouped together based on their life cycle and, consequently, their sensitivity to parasiticides. The aim is to provide readers with key aspects of parasite control and prevention, highlighting those diseases that can be transmitted by them. Geographic distribution maps are also included.

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TARGET AUDIENCE:

✱ Small animal vets. Parasitology ✱ Veterinary nurses ✱ Veterinary students RETAIL PRICE FORMAT:17 × 11 cm NUMBER OF PAGES: 82 NUMBER OF IMAGES: 67 BINDING: paperback, wire-o ISBN: 978-84-17640-10-1

€40

Authors DUNBAR GRAM Service Chief and Clinical Associate Professor of Dermatology at the University of Florida, College of Veterinary Medicine.

JEANMARIE SHORT Board Certified Veterinary Dermatologist.

HEATHER D. STOCKDALE WALDEN Assistant Professor of Parasitology (Department of Comparative, Diagnostic and Population Medicine) at the University of Florida, College of Veterinary Medicine.

KEY FEATURES:

➜ Includes comprehensible illustrations of the life cycles of the most common ectoparasites in small animals. ➜ Describes key aspects of parasite control and prevention. ➜ Provides useful information on ectoparasites, highlighting those diseases that can be trasmitted by them.

Presentation of the book Small animal ectoparasites represent a significant health issue for many pets and humans. Parasiticides have historically been used primarily to prevent animal infestations and disease caused by a specific parasite. Recently, our understanding of the role of parasites in the transmission of certain diseases, including those transmissible to humans, has served to further emphasize the importance of parasite control. This publication will review important small animal ectoparasites including prevention procedures, their life cycle and diseases they may cause or transmit.

hkeita/shutterstock.com

Dunbar Gram DVM, DACVD, MRCVS

Ectoparasites in Small Animals. Life Cycles

The authors Dunbar Gram DVM, DACVD, MRCVS Dr. Gram is Service Chief and Clinical Associate Professor of Dermatology at the University of Florida, College of Veterinary Medicine. He received his undergraduate degree from Wesleyan University in Connecticut and his Doctor of Veterinary Medicine with high honors from Auburn University. He completed an internship at the University of Illinois and a residency in dermatology at North Carolina State University. He has taught dermatology at The University of Edinburgh, The University of Prince Edward Island and North Carolina State University.

Jeanmarie Short DVM, DACVD Jeanmarie Short was a licensed veterinary technician before graduating from the VirginiaMaryland Regional College of Veterinary Medicine. She completed a one year rotating internship in emergency and internal medicine. After three years in general small animal practice, she completed a residency in dermatology at Animal Allergy and Dermatology in Virginia Beach, VA, and is now a Board Certified Veterinary Dermatologist. Her interests are in endocrine and allergic diseases.

Heather D. Stockdale Walden MS, PhD Dr. Walden is Assistant Professor of Parasitology (Department of Comparative, Diagnostic and Population Medicine) at the University of Florida, College of Veterinary Medicine.

She is a member of the American Association of Veterinary Parasitologists (AAVP), and American Society of Parasitologists (ASP). She manages the diagnostic parasitology service in the UF-CVM Parasitology Lab and offers consultation and diagnostic assistance to the Clinical Microbiology, Parasitology and Serology Service in the UF-CVM Small Animal Hospital. Dr. Walden’s research interests focus on zoonotic parasitic disease, diagnosis and classical parasite biology, modes of transmission and pathogenicity in the definitive host. She has lead and collaborated with several research projects throughout the United States, Mexico, Ecuador, the Galapagos Islands, and Zambia and Senegal, Africa.

Table of contents 1. Introduction General importance of parasites Importance of life cycles in parasite control

2. Ticks Description and geographic distribution Hard ticks Soft ticks Life cycle Hard ticks Soft ticks Vector potential and disease transmission Critical points for control and prevention

3. Fleas Description and geographic distribution Life cycle Host component of flea life cycle Environmental component of flea life cycle Vector potential, disease transmission, and economic impact Critical points for control and prevention

4. Mites Description and geographic distribution Demodex mites Critical points for diagnosis, control, and prevention Scabies mites Critical points for diagnosis, control, and prevention Otodectes cynotis/Ear mites Critical points for diagnosis, control, and prevention

Cheyletiella spp./“Walking dandruff” Critical points for diagnosis, control, and prevention

5. Chewing and sucking lice Description and geographic distribution Life cycle Vector potential and disease transmission Critical points for control and prevention

6. Biting flies Biting midges (Ceratopogonidae) Description and geographic distribution Life cycle Vector potential and disease transmission Sand flies (Psychodidae) Description and geographic distribution Life cycle Vector potential and disease transmission Critical points for control and prevention

7. Mosquitoes Description and geographic distribution Life cycle Vector potential and disease transmission Critical points for control and prevention

8. Screwworm flies Description and geographic distribution Life cycle Health concerns Critical points for control and prevention

9. Conclusion Further reading references

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LIFE CYCLES OF ECTOPARASITES Dunbar Gram Jeanmarie Short Heather D. Stockdale Walden

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2 | Ticks

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While D. andersoni is common in the United States (Fig. 7), D. reticulatus is very widespread in Europe (Fig. 8).

Figure 7. Distribution of Dermacentor andersoni in the United States.

Figure 8. Distribution of Dermacentor reticulatus in Europe and Near East.

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2 | Ticks

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Ixodes spp.

Ixodes ticks are found throughout the world. In the United States and Europe, I. scapularis (Figs. 9 and 10) and I. ricinus (Fig. 11) are known to spread Lyme disease. I. pacificus is more present in the West Coast (Fig. 12).

Figure 9. Female Ixodes scapularis.

Image courtesy of Lyle J. Buss, Entomology and Nematology Department, University of Florida, US.

Figure 10.

Distribution of Ixodes scapularis in the United States.

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2 | Ticks

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Haemaphysalis spp.

Haemaphysalis ticks are found throughout the world, although many species are found in Asia.

H. leporispalustris (rabbit tick) is found throughout the Americas. As the common name describes, the preferred host is the rabbit, but it can infest other small mammals. H. longicornis is typically seen in Asia, Australia, and New Zealand (Figs. 15–17). However, in 2017, H. longicornis was found in the United States on livestock with no history of travel outside of the country.

An interesting characteristic of H. longicornis is the ability of some females to reproduce either bisexually or asexually.

Figure 15. Head and scutum of a female Haemaphysalis longicornis. Image courtesy of Dr. Julia Kasper, New Zealand Biosecure Entomology Laboratory.

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2 | Ticks

Figure. 16. Distribution of Haemaphysalis longicornis in Asia.

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Figure 17. Distribution of Haemaphysalis longicornis in Australia and New Zealand.

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2 | Ticks

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Soft ticks

Larvae attach to host and molt to nymphs1 in ear canal

Otobius megnini

Eggs hatch into larvae on ground

Nymphs1 feed on host’s ear canal and molt

Nymphs2 leave ear canal, drop to ground, molt to adults, and mate

The progression of the life stages for O. megnini takes place on the same host, making them a onehost tick. Eggs are hatched on the ground, and larvae find their host by crawling onto vegetation to attach as the animal passes by. The larvae make their way to the ear canal and feed. Larvae molt to the nymphal stage inside the ear canal, where another blood meal is taken. This is followed by development into a second nymphal stage. After feeding, the nymphs leave the ear canal and molt to adults on the ground, where mating occurs (Fig. 24).

Figure 24. One-host life cycle.

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2 | Ticks

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Ornithodoros spp.

Eggs hatch into larvae Mating may be repeated multiple times

Adults feed on host and females lay eggs

6-legged larvae feed on host and molt

8-legged nymphs1 feed on host and molt

Nymphs3 feed on host and molt (may repeat to multiple nymphal stages)

Figure 25. Multi-host life cycle.

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Nymphs2 feed on host and molt

These ticks prefer to live in underground nests, host dens, or wall crevices. They can burrow and delay egg laying until a host is present. Similar to most argasids, Ornithodoros are considered multi-host ticks. Once larvae feed on a host, they drop off and molt into nymphs. These nymphs feed on a new host and drop off to enter another nymphal stage. As many as 3–7 repeated stages can occur, depending on species.

After completing the last nymphal stage, adult ticks can either mate or feed on their host. Adults may feed and reproduce multiple times, with females laying hundreds of eggs after each mating (Fig. 25). some species of Ornithodoros are capable of living for many years.

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Critical points for control and prevention Parasiticides Treatment of hosts

synthetic pyrethroids are associated with toxicity in cats, and should not be used.

The most important aspect of acaricide treatment is the ability to kill a tick before it has an opportunity to transmit disease. Synthetic pyrethroids work quickly; however, there is some evidence of resistance in ticks.

In the last several years, a new class of acaricides has been developed: isoxazolines. They are associated with a fairly fast onset of action (although slower compared to pyrethroids), with greater than 90 % efficacy.

Treatment of the environment Most three-host ticks prefer areas with high grass, weeds, and brush. To control their population, it is important to keep these areas trimmed back and treated regularly with acaricides. For Rhipicephalus ticks, treating indoor environments, such as wall crevices, may be necessary. It is difficult to effectively treat environments with soft ticks due to their ability to burrow and shelter themselves. However, isoxazolines have shown to be effective against argasids during in vitro studies and may have potential for being effective in susceptible hosts.

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Fleas

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LIFE CYCLES OF ECTOPARASITES

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Description and geographic distribution Adult fleas are blood-sucking wingless insects and account for the majority of pathological conditions associated with this parasite. With virtually a worldwide distribution of fleas and an increased public awareness of disease transmission, flea control measures are an important consideration for many pet owners, veterinarians, and the veterinary industry.

Ctenocephalides felis causes more than 92 % of dog infestations and 97 % of cat infestations (Fig. 1). Other flea species that may be of importance in some geographic areas or individual situations include Echidnophaga gallinacea, Pulex irritans, Spilopsyllus cuniculi, and Tunga penetrans.

The biology, development, and life cycle of C. felis has been studied in detail. The points discussed in this section may not apply to other flea species.

Figure 1. Adult flea. Image courtesy of Dr. L. Buss and UF/AFIS.

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4 | Mites

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Critical points for diagnosis, control, and prevention Various opinions exist regarding the two well-categorized follicular dwelling Demodex mites, Demodex canis and Demodex injai, and whether the more controversial mite often referred to as Demodex cornei should be considered different from the nonfollicular mite identified in other animal species.

Without clinical signs, small, typically undetectable numbers of D. canis mites are considered normal. The head and feet are often the first areas to show clinical signs. Multifocal alopecia with variable inflammation and pruritus may be noted with an overgrowth of mites. In severe cases, the disease may be life-threatening.

Deep skin scrapings or hair plucks confirm the presence of mites, but other techniques may also be used. It is important to consider the potential for a genetic defect, underlying disease process, or concurrent drug use to be contributing factors in most cases of demodicosis. Treatment is pursued if signs are severe or if multiple body regions are affected.

For dogs with clinical signs associated with an overgrowth of Demodex mites, significant advancements have been made regarding the safety, ease, and convenience of treatment.

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4 | Mites

Traditional feline demodicosis caused by Demodex cati mimics canine demodicosis caused by Demodex canis. The mites have a similar appearance and pathogenesis. Treatment can be challenging due to the underlying disease and limited therapies approved for cats.

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Our understanding of demodicosis in general and feline demodicosis in particular has evolved due to the identification of a contagious species, Demodex gatoi.

Unlike other Demodex mites, Demodex gatoi is an easily transmitted and contagious, surface dwelling mite that typically causes pruritus. It can be difficult to find on skin scrapes and fecal examination. Essentially, it behaves like a scabies mite but looks like a short/stubby Demodex mite. The mite is more common in some geographic locations and virtually never diagnosed in others. Pruritus and alopecia are typical signs, but some cats may be asymptomatic yet be positive on skin scrapes or fecal examination. For this reason, all cats in the household should be treated. At the current time, very limited treatment options exist for this disease.

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5 | Chewing and suCking LiCe

0.2 mm

Figure 1. Trichodectes canis (50×).

Photo by Dr. Heather S. Walden, Department of Comparative, Diagnostic and Population Medicine, University of Florida, US.

0.2 mm

0.1 mm

Figure 2. Linognathus setosus (60×). Photo by Dr. Heather S. Walden,

Figure 3. Felicola subrostratus (80×). Photo by Dr. Heather S. Walden,

Department of Comparative, Diagnostic and Population Medicine, University of Florida, US.

Department of Comparative, Diagnostic and Population Medicine, University of Florida, US.

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5 | Chewing and suCking LiCe

Life cycle Lice are very small, averaging 2–3 mm in length.

Gravid females lay their eggs, or nits, firmly attached to an individual hair of the canine or feline host.

Within 2 weeks, the eggs hatch and the newly emerged nymphs will remain on the host and go through a series of molts to develop into a mature adult within a month (Fig. 4). Adult lice can survive up to a month or more on the host. Some species can survive off the host for a short period of time; however, most need constant contact with their host and many are very sensitive to temperature.

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Chewing lice feed on epidermal scales and sebaceous secretions, while sucking lice feed on blood

Nymphs undergo 3 molts to a sexually mature adult Lice spend their entire lives on the outside of host (in hair or fur coat)

Nymphs (smaller than mature adults) emerge as eggs hatch

Adult females cement eggs, or nits, to individual hairs

Figure 4. Life cycle of chewing and sucking lice.

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8 | Screwworm flieS

1 mm

2 mm

Figure 2. Third-stage larva of Cochliomyia hominivorax.

Figure 3. Adult Cochliomyia hominivorax.

Photo by Dr. Heather S. Walden, Department of Comparative, Diagnostic and Population Medicine, University of Florida, US.

Photo by Dr. Heather S. Walden, Department of Comparative, Diagnostic and Population Medicine, University of Florida, US.

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8 | Screwworm flieS

Life cycle The life cycle of C. hominivorax begins with the females laying their eggs in the living tissue of a vertebrate host. Eggs hatch within 11–21 hours. The larval or maggot stage goes through three developmental stages, or instars, as it feeds on the host tissue. This takes up to 8 days. It will then leave the host, dropping to the ground to pupate and with an adult fly emerging soon after (Fig. 4). The life cycle of C. bezziana is very similar to that of C. hominivorax.

However, hatching can occur within 12–16 hours and the pupal stage can last up to 10 days.

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Adult flies emerge soon after, mate, and continue the life cycle

Females lay eggs in living tissue of vertebrate hosts.

They can lay thousands of eggs in their lifetime After approximately 1 week, larvae drop to the ground and pupate

Eggs hatch quickly and larvae begin to feed on host tissue and develop

Figure 4. Life cycle of Cochliomyia hominivorax.

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