5.1 Ectoparasites: Mites, Ticks, and Lice

Mites, ticks, and lice are tiny terrors that make a big impact. These ectoparasites live on or burrow into their hosts, causing itching, skin problems, and disease. They're not just annoying – they can seriously affect animal health and production.

These pests have complex life cycles and clever ways of spreading. Some spend their whole lives on one host, while others hop from animal to animal. They can cause everything from mild irritation to severe illness, and some even transmit dangerous diseases to humans.

Ectoparasitic Arthropod Groups

Mites (Subclass Acari)

• Small, eight-legged arthropods with a simple body structure where the head, thorax, and abdomen are fused into a single body segment
• Sarcoptic mange mites (Sarcoptes scabiei) are obligate parasites that burrow into the skin of their hosts causing intense itching and dermatitis
• Demodex mites (Demodex spp.) are normal inhabitants of hair follicles and sebaceous glands in mammals but can cause demodicosis when present in large numbers
• Other examples include ear mites (Otodectes cynotis) in dogs and cats and psoroptic mange mites (Psoroptes ovis) in sheep and cattle

Ticks (Order Ixodida)

• Larger, blood-feeding ectoparasites with a complex life cycle capable of transmitting various pathogens to their hosts
• Hard ticks (Ixodidae) have a hard, sclerotized dorsal shield called a scutum and are known vectors of diseases such as Lyme disease (Borrelia burgdorferi), Rocky Mountain spotted fever (Rickettsia rickettsii), and babesiosis (Babesia spp.)
• Soft ticks (Argasidae) lack a scutum and typically feed on their hosts for shorter periods transmitting pathogens such as African swine fever virus and relapsing fever spirochetes (Borrelia spp.)
• Examples of hard ticks include the black-legged tick (Ixodes scapularis) and the American dog tick (Dermacentor variabilis), while soft ticks include the fowl tick (Argas persicus) and the relapsing fever tick (Ornithodoros spp.)

Lice (Order Phthiraptera)

• Wingless, flattened insects that are obligate ectoparasites spending their entire life cycle on the host
• Sucking lice (Anoplura) have piercing-sucking mouthparts and feed on the blood of their hosts potentially causing anemia and vectoring diseases such as epidemic typhus (Rickettsia prowazekii) and trench fever (Bartonella quintana)
• Chewing lice (Mallophaga) have mandibulate mouthparts and feed on skin debris, feathers, or fur leading to irritation, feather damage, and decreased egg production in poultry
• Examples of sucking lice include the human body louse (Pediculus humanus humanus) and the dog sucking louse (Linognathus setosus), while chewing lice include the chicken body louse (Menacanthus stramineus) and the cat louse (Felicola subrostratus)

Life Cycles and Transmission of Ectoparasites

Mite Life Cycles and Transmission

• Mites typically have a four-stage life cycle consisting of egg, larva, nymph, and adult with some species completing their entire life cycle on a single host while others may have free-living stages
• Sarcoptic mange mites are transmitted through direct contact with an infected host or contaminated environment, with female mites burrowing into the skin to lay eggs and perpetuate the infestation
• Demodex mites are considered part of the normal fauna and are typically transmitted from mother to offspring during nursing, but overpopulation can lead to clinical signs of demodicosis
• Ear mites are highly contagious and can be transmitted through direct contact with an infected animal or contaminated bedding and grooming equipment

Tick Life Cycles and Transmission

• Ticks have a complex life cycle that includes egg, larva, nymph, and adult stages, with most species requiring multiple hosts to complete their development
• Hard ticks undergo a three-host life cycle, with each active stage (larva, nymph, and adult) feeding on a different host before detaching and molting to the next stage
• Soft ticks have a multi-host life cycle, with multiple nymphal stages that feed on different hosts, and adults that feed and mate on the host before females lay eggs in the environment
• Ticks can transmit pathogens to their hosts during blood feeding through salivary secretions, with some pathogens, such as Borrelia burgdorferi (Lyme disease), maintained through transstadial transmission within the tick
• Ticks can also transmit pathogens transovarially, where the pathogen is passed from an infected female tick to her offspring

Lice Life Cycles and Transmission

• Lice have a simple life cycle consisting of egg, nymph, and adult stages, which are completed entirely on the host
• Female lice attach their eggs (nits) to the hair shafts or feathers of the host, with nymphs hatching from the eggs and undergoing several molts before reaching the adult stage
• Lice are typically transmitted through direct contact with an infested host or contaminated objects such as clothing, bedding, or grooming equipment
• Some lice species, such as the human pubic louse (Pthirus pubis), can also be transmitted through sexual contact

Clinical Signs of Ectoparasite Infestations

Mite Infestation Clinical Signs

• Sarcoptic mange is characterized by intense pruritus (itching), erythema (redness), papules, and crusts, which can lead to self-trauma, secondary bacterial infections, and thickening of the skin (lichenification) in severe cases
• Demodicosis can cause localized or generalized hair loss, erythema, scaling, and pustules, with severe, widespread skin lesions in immunocompromised animals
• Ear mite infestations cause otitis externa, characterized by ear canal inflammation, dark, waxy discharge, and head shaking or ear scratching

Tick Infestation Clinical Signs

• Heavy tick burdens can lead to anemia, particularly in young or small animals, and local irritation and inflammation at the attachment site
• Clinical signs associated with tick-borne diseases vary depending on the pathogen but may include fever, lethargy, anorexia, joint pain, neurological signs, and anemia
• Tick paralysis, caused by neurotoxins in the saliva of certain tick species, can lead to ascending flaccid paralysis, respiratory distress, and death if the tick is not removed

Lice Infestation Clinical Signs

• Sucking lice infestations can lead to anemia, particularly in heavy infestations, with animals exhibiting restlessness, rubbing, and self-trauma
• Chewing lice can cause feather damage, scaliness, and pruritus in birds, leading to decreased weight gain and egg production in severe cases
• Pediculosis in humans is characterized by intense itching and the presence of nits on the hair shafts, with secondary bacterial infections occurring due to scratching
• Infestations with the human body louse can lead to skin irritation, pruritus, and the development of characteristic "vagabond's disease" skin lesions

Economic and Veterinary Significance of Ectoparasites

Livestock and Poultry Production Impacts

• Mite infestations, such as sarcoptic mange and psoroptic mange, can cause decreased weight gain, reduced milk production, and skin damage, leading to economic losses in cattle, sheep, and goats
• Tick infestations can lead to reduced growth rates, decreased milk production, and anemia in livestock, with the cost of tick control measures and treatment of tick-borne diseases contributing to economic losses
• Lice infestations in poultry can result in decreased egg production, reduced feed conversion efficiency, and increased susceptibility to other diseases
• The development and implementation of effective ectoparasite control strategies, such as acaricides, insecticides, and integrated pest management, require significant investment in livestock and poultry production systems

Companion Animal Health and Welfare Impacts

• Mite infestations, such as sarcoptic mange and ear mites (Otodectes cynotis), are common causes of skin disease in dogs and cats, leading to discomfort and decreased quality of life
• Tick-borne diseases, such as Lyme disease, ehrlichiosis, and anaplasmosis, can cause serious illness in dogs and cats, requiring prompt veterinary treatment
• Flea infestations (Ctenocephalides spp.) are a common problem in companion animals, causing dermatitis, anemia, and potentially transmitting other parasites such as tapeworms
• The cost of treating ectoparasite-related diseases in companion animals can be substantial for pet owners, and the emotional toll of seeing pets suffer from these conditions can be significant

Zoonotic Disease Risks and Public Health Implications

• Ticks can transmit pathogens such as Borrelia burgdorferi (Lyme disease), Rickettsia rickettsii (Rocky Mountain spotted fever), and Francisella tularensis (tularemia) to humans, leading to potentially serious illnesses
• Sarcoptic mange mites can cause scabies in humans, leading to intense itching and skin lesions, which can be difficult to diagnose and treat effectively
• Lice infestations, particularly head lice (Pediculus humanus capitis), are a common problem in school-aged children and can lead to social stigma and missed school days
• The economic impact of ectoparasites extends beyond direct losses in animal production and includes the costs of control measures, treatments, and public health interventions to manage zoonotic diseases