Demodex phylloides (Demodectic Mange)
LEVELS: Highly unlikely: No controls necessary; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission; Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s); Minor: Low prevalence, typically non-lethal infection with recovery very likely; Negligible: Little or no market disruption when disease occurs on one or more farms; Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments; Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy; Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations; No availability: Effective vaccines not currently available in the US (or have not been developed); Not feasible: Eradication extremely unlikely
Criteria Levels
- Foodborne Zoonotic Transmission: No evidence of transmission
- Non-Foodborne Zoonotic Transmission: No evidence of transmission
- Beyond-Farm Spread Potential: Farm biosecurity effective
- Detection Difficulty: Moderate: confirmation once suspected
- Financial Impact - Mortality and Morbidity Costs: Limited losses (few pigs)
- Financial Impact - Prevention and Control Costs: Little market disruption
- Antimicrobial Resistance - Pathogen Risk: Low resistance risk
- Antimicrobial Resistance - Treatment Impact: Minimal: Rare or short-course individual treatments
- Treatment Availability: Limited effectiveness
- Vaccine Availability: No effective vaccine or bacterin available
- Eradication Feasibility: Not feasible or extremely unlikely
Overview
Demodectic mange (demodicosis, follicular mange) is relatively unimportant in swine compared to sarcoptic mange. Caused by Demodex phylloides, an elongate mite that lives inside hair follicles, it is quite common in subclinical form as Demodex mites are considered normal skin flora in mammals. Clinical disease is uncommon and characterized by nodular lesions containing mites and hyperkeratotic debris. Unlike sarcoptic mange, treatment of clinical demodicosis in swine has not been successfully documented.
Detailed Justification
1. Foodborne Zoonotic Transmission
Level: No evidence of transmission
Demodex mites are strictly adapted to their host species and reside within hair follicles. There is no mechanism for foodborne transmission. The parasite cannot survive outside the skin environment.
2. Non-Foodborne Zoonotic Transmission
Level: No evidence of transmission
D. phylloides is host-specific to swine. Demodex species are highly host-adapted - each mammalian species has its own Demodex species. Human demodicosis is caused by different species (D. folliculorum, D. brevis), and cross-species transmission does not occur.
3. Beyond-Farm Spread Potential
Level: Farm biosecurity effective
The mite has very limited environmental survival: - "The mites can survive for several days in moist environments and up to 21 days under experimental conditions in pieces of skin kept cool and moist" - "The mites can survive only 1 or 2 days if removed from the hosts' skin and are killed by desiccation in as little as one hour at 20°C on the skin surface" - "Transmission of the mites probably occurs by direct contact with neonates while nursing or huddling"
The extremely limited off-host survival means biosecurity focused on animal introductions is effective.
4. Detection Difficulty
Level: Moderate: confirmation once suspected
Clinical signs can suggest the diagnosis, but confirmation requires laboratory examination: - "The diagnosis of demodicosis is made by finding numerous mites in deep skin scrapings" - "Plucked hair may also reveal mites" - "Because mites are present in nearly all swine, identification of a few mites does not necessarily prompt a diagnosis of demodicosis" - A correlation between mite numbers, immature stages, and visible lesions must be established
The need for deep skin scrapings and the ubiquitous nature of subclinical carriage complicate definitive diagnosis.
5. Financial Impact - Mortality and Morbidity Costs
**Level: Limited losses (few pigs)
The chapter clearly indicates minimal impact: - "Demodectic mange is relatively unimportant in swine" - Most infections are subclinical ("common in the subclinical form") - Clinical disease is uncommon - Lesions may be "confused with swine pox" but do not cause significant production losses
When clinical disease occurs, it affects individual animals rather than causing herd-wide problems.
6. Financial Impact - Prevention and Control Costs
Level: Little market disruption
Demodectic mange is not a regulated disease. There are no trade restrictions, surveillance requirements, or market access issues. The primary concern would be occasional carcass trimming if nodular lesions are present.
7. Antimicrobial Resistance - Pathogen Risk
Level: Low resistance risk
Demodicosis is treated with acaricides, not antimicrobials. This criterion does not apply in the traditional AMR sense.
8. Antimicrobial Resistance - Treatment Impact
Level: Minimal: Rare or short-course individual treatments
Treatment involves acaricides, not antibiotics. There is no antimicrobial selection pressure. Additionally, treatment is rarely attempted in swine due to the low clinical importance of the disease.
9. Treatment Availability
Level: Limited effectiveness
The chapter explicitly states treatment limitations: - "There are no reports of successful treatment of swine demodicosis with any acaricide" - "Ivermectin or amitraz are successful in canine demodicosis" but this has not been demonstrated in swine - "It may be prudent to cull severely infected pigs"
This represents a significant limitation - while products exist, their efficacy in swine demodicosis is not established.
10. Vaccine Availability
Level: No effective vaccine or bacterin available
No vaccine exists for demodicosis. The chapter mentions potential genetic predisposition (as occurs in dogs), suggesting that culling may be more appropriate than attempting immunization or treatment.
11. Eradication Feasibility
Level: Not feasible or extremely unlikely
Eradication is not feasible because: - "Demodex mites are thought to be normal skin flora in mammals" - Subclinical carriage is common ("quite common in the subclinical form") - The mites are part of the normal skin microbiome and colonize pigs during nursing
Attempting to eradicate a commensal organism present in virtually all swine is neither practical nor necessary.
Summary
Demodex phylloides causes demodectic (follicular) mange in swine, residing within hair follicles alongside hair shafts. Unlike sarcoptic mange, demodicosis is relatively unimportant clinically - the mite is considered normal skin flora, and subclinical carriage is common. Clinical disease, when it occurs, presents as nodular lesions primarily on the snout, eyelids, jowls, and ventral body. Diagnosis requires deep skin scrapings and correlation of mite numbers with clinical lesions. Significantly, there are no reports of successful treatment of swine demodicosis with any acaricide - culling of severely affected animals is recommended. Eradication is not feasible as the organism is a normal commensal. The practical approach is to accept subclinical carriage while culling the rare animals with clinical disease.