How do ticks bite humans: characteristic skin marks?

The Tick's Anatomy and Biting Mechanism

Mouthparts and Their Function

Hypostome: The Anchor

The hypostome is a hardened, barbed structure located on the ventral tip of a tick’s mouthparts. Its primary function is to secure the tick to the host’s skin during blood ingestion. The barbs penetrate the epidermis and embed in the dermal layer, creating a mechanical lock that resists displacement even when the host moves or scratches.

During attachment, the hypostome works together with the chelicerae, which cut a shallow incision, and the surrounding cement glands, which secrete a proteinaceous adhesive. The combined action produces a puncture wound characterized by a central dark spot where the hypostome resides, surrounded by a ring of mild erythema. The wound often remains visible for several days after the tick detaches, sometimes developing a small ulceration if the feeding period was prolonged.

Key characteristics of the hypostome‑induced skin mark:

Central puncture point, typically 0.5–2 mm in diameter, corresponding to the hypostome’s size.
Surrounding erythematous halo, reflecting localized inflammation.
Possible formation of a small scab or ulcer if the tick was attached for more than 48 hours.
Absence of a raised bump; the mark is flat or slightly depressed.

The barbed design prevents the tick from being easily removed, which reduces the likelihood of premature detachment and minimizes host awareness of the feeding event. Consequently, the hypostome contributes directly to the subtle, often overlooked skin lesions associated with tick bites.

Chelicerae: The Cutters

Ticks attach to human skin by inserting their mouthparts. The first structures to penetrate the epidermis are the chelicerae, a pair of hardened, blade‑like appendages located at the front of the hypostome. Each chelicera consists of a basal segment anchored to the gnathosoma and a distal, serrated cutting edge that functions as a miniature scalpel.

During attachment, the chelicerae slice through the stratum corneum and superficial dermis, creating two parallel incisions. The cuts are typically 0.5–1 mm in length, spaced 0.2–0.3 mm apart, and oriented along the tick’s forward axis. As the chelicerae retract, the incisions remain open, forming a characteristic double‑track mark. The surrounding tissue may exhibit mild erythema, but the primary visual cue is the paired linear scratches.

Recognition of these marks assists clinicians in distinguishing tick bites from other arthropod injuries. Typical features include:

Two narrow, parallel lines of equal length
Alignment with the direction of the tick’s body
Absence of a central puncture wound (the hypostome inserts deeper but does not produce an external scar)

Understanding the role of the chelicerae clarifies why tick bites produce a distinct double‑track pattern and supports accurate field identification.

Saliva: A Complex Cocktail

Tick saliva is a highly specialized secretion that enables prolonged attachment and blood ingestion while minimizing host detection. It contains a mixture of biologically active molecules that manipulate hemostasis, immunity, and pain perception.

Key functional groups in the saliva include:

Anticoagulants such as apyrase and thrombin inhibitors that prevent clot formation.
Immunomodulatory proteins that suppress cytokine release and inhibit complement activation.
Analgesic peptides that reduce nociceptive signaling at the bite site.
Anti‑inflammatory agents that limit edema and erythema.
Enzymes, for example metalloproteases, that degrade extracellular matrix components and facilitate mouthpart penetration.

The coordinated action of these compounds creates a microenvironment where blood flows freely, inflammatory responses are dampened, and the host often experiences only a faint or transient skin mark. The specific composition varies among tick species, reflecting adaptation to different hosts and feeding durations. Research consistently demonstrates that the complexity of the salivary cocktail directly influences the appearance, size, and persistence of the lesions observed after a tick bite.

The Biting Process: From Attachment to Feeding

Finding a Host: Questing Behavior

Ticks locate a blood meal through a behavior known as questing. The arthropod climbs onto vegetation, extends its forelegs, and waits for a passing host. Questing height varies with species, life stage, and environmental humidity; nymphs often position themselves a few centimeters above leaf litter, while adults may ascend taller grasses or shrubs. Sensory organs on the forelegs detect carbon dioxide, heat, and vibrations, triggering a rapid grasp when a suitable host brushes against the plant.

When a human brushes past a questing tick, the parasite clamps onto the skin with its chelicerae and inserts its hypostome, a barbed feeding tube. The initial attachment leaves a small puncture surrounded by a pale, sometimes raised area. As the tick feeds, saliva containing anticoagulants and anti‑inflammatory compounds creates a localized erythema that may expand into a target‑shaped lesion, commonly called a “bull’s‑eye” rash. The size and shape of this mark depend on the tick’s attachment duration and the host’s immune response.

Attaching to the Skin: The Initial Grip

Ticks begin feeding by securing a firm attachment to the host’s epidermis. The process starts when the tick climbs onto the skin and searches for a suitable site, often a warm, moist area such as the scalp, armpits, or groin. Using its front legs equipped with sensory organs, the tick detects heat, carbon‑dioxide, and movement, then anchors itself.

The attachment proceeds through several precise actions:

The tick inserts its hypostome, a barbed, tube‑like structure, into the epidermis.
Salivary glands release a mixture of anticoagulants, anesthetics, and anti‑inflammatory compounds, preventing clotting and masking the bite.
The barbs on the hypostome lock the mouthparts in place, creating a stable grip that resists removal.
The tick’s cement glands secrete a proteinaceous glue that hardens around the feeding site, further reinforcing the attachment.

This initial grip establishes a direct channel between the tick’s mouthparts and the host’s blood vessels, enabling the parasite to begin engorgement within minutes. The combination of mechanical anchoring and biochemical secretions makes early removal difficult and determines the characteristic puncture mark that may later appear on the skin.

Penetrating the Skin: A Painless Invasion

Ticks attach by inserting a barbed hypostome, a rigid structure equipped with backward‑pointing teeth. The hypostome penetrates the epidermis and dermis in a single, swift motion, anchoring the arthropod without the need for repeated probing. Salivary secretions contain anticoagulants and vasodilators that keep blood flowing and mask the wound’s pain receptors.

The bite is typically painless because the saliva also includes anesthetic compounds. The host rarely perceives the initial attachment; awareness often arises only after the tick has been feeding for several hours.

Typical cutaneous signs after attachment include:

A small, pinpoint puncture at the center of the feeding site.
A surrounding erythematous halo, often 2–5 mm in diameter.
A localized wheal or papule that may develop a central necrotic spot in some species.
A “target” or bull’s‑eye pattern, especially with certain tick‑borne infections, characterized by concentric rings of redness and pallor.

These marks persist for days to weeks, gradually fading as the skin heals. Their appearance, size, and evolution help differentiate tick bites from other arthropod assaults and guide clinical assessment.

Cementing the Bite: A Firm Hold

Ticks attach by inserting their hypostome—a barbed, serrated feeding organ—into the dermis. Salivary secretions contain cement proteins that rapidly harden, forming a stable anchor that resists host grooming and blood flow. The cement creates a microscopic plaque around the hypostome, locking the mouthparts in place for several days.

Key aspects of the cementing process:

Composition: Glycoproteins, lipids, and enzymes that polymerize upon contact with skin tissue.
Timing: Solidification begins within minutes of attachment; full strength is achieved in under an hour.
Function: Prevents detachment, minimizes host inflammatory response, and facilitates prolonged blood ingestion.

The resulting skin mark reflects this mechanism. A small, dome‑shaped papule appears at the attachment site, often surrounded by a faint erythematous halo. The central puncture may be obscured by the hardened cement, making the lesion appear smoother than a typical insect bite. If the tick is removed before cement dissolution, the bite mark may persist as a slightly raised scar.

Characteristic Skin Marks and Reactions

Immediate Reactions: Erythema and Papules

Ticks attach to the skin with a hypostome that penetrates the epidermis and dermis, delivering saliva that contains anticoagulants and anesthetics. Within minutes of attachment, most individuals develop a localized erythema, a redness that spreads outward from the bite site. The erythema typically appears as a pink to reddish halo, often symmetric, and may reach a diameter of 2–5 cm. Its onset is rapid, usually within 30 minutes to a few hours, and it may persist for several days before fading.

In addition to redness, many victims notice small papules that emerge at the attachment point. These papules are raised, firm, and may be flesh‑colored or slightly erythematous. They often measure 1–3 mm in height and can be palpable. Papules may co‑occur with a central punctum, the site where the tick’s mouthparts entered the skin. Their presence is an early indicator of a tick bite, especially when the engorged arthropod has been removed before the formation of a classic “bull’s‑eye” lesion.

Key features of the immediate skin response include:

Onset: 30 min – 3 h after attachment.
Erythema: Diffuse, pink‑red halo, 2–5 cm diameter, may expand slowly.
Papules: 1–3 mm raised nodules, often centered on the bite punctum.
Duration: Redness fades in 3–7 days; papules resolve within 1–2 weeks.
Symptoms: Mild itching or tingling; pain is uncommon due to tick‑delivered anesthetic.

Differentiating these early signs from other arthropod bites is essential for prompt identification of tick exposure. The combination of a rapidly appearing erythematous halo and a central papule, especially in outdoor or endemic areas, strongly suggests a tick bite and warrants inspection for a retained mouthpart and consideration of prophylactic measures.

Delayed Reactions: Localized Swelling and Itching

Ticks often trigger a reaction that appears hours to days after the bite. The latency reflects the host’s immune response to salivary proteins introduced during feeding.

Localized swelling typically presents as a firm, raised area surrounding the attachment site. The edematous zone may expand up to several centimeters in diameter, sometimes forming a palpable nodule. The skin over the swelling remains intact, without ulceration or necrosis.

Itching accompanies the edema in most cases. The pruritus can be intermittent or persistent, intensifying when the area is warm or irritated. Scratching may exacerbate the swelling and increase the risk of secondary bacterial infection.

Key clinical features of a delayed tick‑bite reaction include:

Onset 12–72 hours after removal of the tick
Well‑defined, non‑fluctuant swelling
Moderate to severe pruritus
Absence of systemic signs such as fever or malaise

Recognition of these signs aids differentiation from early allergic responses, Lyme disease erythema migrans, or bacterial cellulitis. Persistent or rapidly expanding lesions warrant further evaluation for secondary infection or tick‑borne pathogens.

Management consists of:

Gentle cleansing of the site with antiseptic solution.
Application of topical corticosteroids to reduce inflammation.
Oral antihistamines for pruritus control.
Monitoring for signs of infection; initiate antibiotics if erythema spreads, warmth increases, or purulence develops.

Prompt treatment limits discomfort, prevents complications, and supports accurate assessment of any underlying tick‑related disease.

The Bull's-Eye Rash: A Sign of Concern

Borrelia burgdorferi and Lyme Disease

Borrelia burgdorferi is a spirochete transmitted primarily by Ixodes ticks during blood meals. The organism enters the host through the tick’s mouthparts, which remain embedded in the skin for up to several days, providing a conduit for bacterial migration.

The earliest cutaneous sign of infection is erythema migrans, a expanding erythematous lesion that typically appears 3‑30 days after the bite. Characteristics include:

Diameter of 5 cm or greater, often exceeding 10 cm.
Central clearing that may produce a “bull’s‑eye” appearance.
Uniform redness at the periphery, sometimes accompanied by mild warmth or itching.
Absence of vesiculation or necrosis in the initial stage.

Serologic testing for IgM and IgG antibodies against B. burgdorferi supports diagnosis after the lesion has persisted for several weeks. Polymerase‑chain‑reaction assays of skin biopsy specimens can confirm the presence of spirochete DNA when serology is equivocal.

Recommended therapy consists of doxycycline (100 mg twice daily for 10–21 days) for most patients; amoxicillin or cefuroxime serve as alternatives for pregnant women and young children. Prompt antimicrobial treatment halts progression to disseminated disease, which may involve cardiac, neurologic, or musculoskeletal complications.

Preventive measures focus on tick avoidance: use of repellents containing DEET or picaridin, wearing long sleeves and trousers, and performing thorough body checks after outdoor exposure. Prompt removal of attached ticks within 24 hours reduces the likelihood of bacterial transmission and subsequent skin manifestation.

Other Potential Skin Manifestations

Allergic Responses

Ticks attach to human skin, insert their mouthparts, and secrete saliva that contains anticoagulants and immunogenic proteins. The bite site often presents a small, erythematous papule or a faint, circular discoloration known as an “engorgement halo.” In addition to these primary marks, the host’s immune system may generate allergic responses that modify the appearance and symptoms of the lesion.

Allergic reactions to tick saliva are classified by onset and mechanism. Immediate hypersensitivity (Type I) appears within minutes to hours, producing pruritus, wheal‑and‑flare swelling, and sometimes urticaria around the bite. Delayed hypersensitivity (Type IV) emerges after 24–72 hours, manifesting as a larger, indurated plaque, erythema, and persistent itching. Systemic allergic manifestations—such as fever, malaise, or generalized rash—can accompany severe local responses, particularly after multiple bites or exposure to highly immunogenic tick species.

Typical allergic signs include:

Localized itching that intensifies after the initial bite.
Swelling that exceeds the size of the primary papule.
Erythematous ring or target‑shaped lesion forming around the bite.
Development of a vesicular or pustular rash within days.
Secondary skin changes, such as hyperpigmentation, persisting for weeks.

Recognition of these allergic patterns assists clinicians in distinguishing simple tick bites from immune‑mediated complications, guiding appropriate antihistamine or corticosteroid therapy and preventing unnecessary antibiotic use.

Secondary Infections

Tick bites often leave a small, red papule that may develop a central puncture mark. When the skin barrier is breached, bacteria, viruses, or fungi from the tick’s mouthparts or the surrounding environment can colonize the wound, producing secondary infections.

Common organisms include Staphylococcus aureus, Streptococcus pyogenes, and Borrelia species that may cause localized cellulitis, lymphangitis, or necrotic ulcers. Symptoms such as increasing redness, swelling, warmth, pus formation, or escalating pain indicate bacterial involvement. Fever, chills, and regional lymphadenopathy suggest systemic spread.

Management requires prompt identification and treatment:

Clean the bite site with antiseptic solution.
Apply a sterile dressing to reduce contamination.
Initiate oral antibiotics targeting gram‑positive cocci (e.g., doxycycline, amoxicillin‑clavulanate) if signs of infection appear.
Seek medical evaluation for rapidly expanding lesions, necrosis, or systemic symptoms.

Prevention of secondary infection relies on immediate removal of the tick, thorough washing of the area, and monitoring for changes over 48–72 hours. Early intervention limits tissue damage and reduces the risk of complications such as septic arthritis or osteomyelitis.

Identifying and Removing a Tick Bite

Visual Inspection: What to Look For

Tick Presence and Appearance

Ticks attach to humans during outdoor activities in grassy, wooded, or brush‑covered areas. Attachment occurs when a questing tick grasps skin, inserts its hypostome, and begins feeding. The process can last from several hours to days, during which the parasite remains visible on the host.

Adult hard ticks (Ixodidae) present a flattened, oval body measuring 2–5 mm when unfed. Color ranges from reddish‑brown to dark brown, occasionally with a lighter scutum on the dorsal surface. As blood intake proceeds, the abdomen expands, reaching 10–15 mm and a glossy, gray‑white appearance. Nymphs are smaller (1–2 mm) and less conspicuous, while larvae are microscopic and rarely observed without magnification.

Typical attachment sites include scalp, behind ears, neck, armpits, groin, and behind knees—areas where skin folds create a protected microenvironment. The bite mark often appears as a small, firm papule surrounding the tick’s mouthparts. After removal, a central puncture may persist, sometimes surrounded by a faint erythematous halo.

Key visual indicators of a tick bite:

Visible arthropod attached to skin, head or mouthparts embedded
Oval, raised lesion matching tick size (2–15 mm depending on engorgement)
Absence of pus or ulceration at initial stage
Possible surrounding erythema, typically uniform in color
Location in a protected skin fold or hair‑covered region

Recognition of these features enables prompt removal and reduces the risk of pathogen transmission.

Surrounding Skin Changes

Ticks attach to the skin with a specialized mouthpart that creates a small puncture. The surrounding tissue reacts promptly, producing visible alterations that help identify the bite.

Typical skin responses include:

Erythema – a red halo 2‑5 mm in diameter, often symmetrical around the attachment site.
Edema – localized swelling that may extend several centimeters from the punctum.
Papule or nodule – raised, firm area that can persist for days.
Vesicle or bulla – fluid‑filled blister, occasionally forming when the host’s immune response is vigorous.
Erythema migrans – expanding annular rash, diameter increasing 2–3 cm per day, characteristic of certain tick‑borne infections.
Necrosis – focal tissue death, presenting as a darkened or ulcerated patch, more common with prolonged attachment.
Secondary infection signs – purulent discharge, increasing warmth, and tenderness indicating bacterial colonisation.

Temporal patterns are predictable. Immediate erythema and edema appear within minutes to hours. Papular or vesicular changes develop over 12–48 hours. Erythema migrans typically emerges 3–7 days after the bite, expanding outward while the central area may remain pale. Necrotic lesions and secondary infections often require longer exposure, manifesting after several days of unattended attachment.

Recognition of these peripheral alterations enables early diagnosis, informs decisions on prophylactic treatment, and reduces the risk of complications associated with tick‑borne pathogens.

Proper Tick Removal Techniques

Using Tweezers: The Recommended Method

Ticks attach firmly, embedding their mouthparts in the epidermis. Prompt removal reduces the risk of pathogen transmission and limits the size of the resulting erythema.

Fine‑point tweezers provide the most reliable grip on the tick’s body. The instrument’s narrow tips allow the operator to grasp the parasite as close to the skin as possible, preventing the legs from breaking off and remaining embedded.

Recommended removal procedure

Disinfect the tweezers with alcohol or an antiseptic wipe.
Grasp the tick’s head or thorax, avoiding the abdomen where the body expands after feeding.
Apply steady, downward pressure to pull the tick straight out; do not twist or jerk.
Release the tick into a sealed container for identification or disposal.
Clean the bite site with antiseptic solution and cover with a sterile bandage if necessary.

After extraction, inspect the wound for residual mouthparts. If any fragment remains, repeat the grip-and-pull action with fresh tweezers. Observe the area for signs of expanding redness, swelling, or flu‑like symptoms; seek medical evaluation if such indicators appear.

Avoiding Common Mistakes: Crushing and Twisting

Ticks attach to the skin with a barbed mouthpart that can remain embedded if the insect is mishandled. Improper removal techniques, especially crushing the body or twisting the tick, increase the likelihood of pathogen transmission and cause additional tissue damage.

Crushing the tick releases its internal fluids, which may contain bacteria, viruses, or protozoa. The expelled material can contaminate the bite site, provoking localized inflammation and elevating the risk of infection. Moreover, a crushed tick becomes difficult to identify, complicating any subsequent medical assessment.

Twisting the tick applies torque to the mouthparts, often breaking them off within the skin. Retained fragments act as a foreign body, prolonging attachment and providing a conduit for pathogens to enter deeper tissues. The resulting wound may bleed, become ulcerated, or develop a persistent lesion.

Correct removal procedure:

Use fine‑pointed, non‑slipping tweezers; grasp the tick as close to the skin as possible.
Apply steady, gentle pressure directly outward, avoiding any squeezing motion.
Release the tick in a sealed container for proper disposal; do not crush it in the hand.
Clean the bite area with antiseptic and monitor for erythema, expanding rash, or fever.

Avoid these practices:

Pinching the tick’s abdomen.
Rotating or wiggling the instrument while the tick is still attached.
Pulling with excessive force that tears skin.

Adhering to the precise pulling technique eliminates the tick intact, minimizes tissue trauma, and reduces the chance of characteristic skin marks developing from secondary infection.

After Removal: Cleaning and Monitoring

After a tick is detached, the bite area should be washed immediately with soap and water. Apply an antiseptic such as povidone‑iodine or chlorhexidine, then cover with a clean, non‑adhesive dressing if the skin is irritated.

Monitoring the site for at least four weeks is essential. Observe for:

Redness expanding beyond the immediate margin
Swelling or warmth
Formation of a pustule or ulcer
Persistent itching or pain
Flu‑like symptoms, fever, headache, muscle aches, or joint pain

If any of these signs appear, seek medical evaluation promptly. Document the date of removal, the tick’s developmental stage, and any observed changes; this information assists clinicians in assessing the risk of vector‑borne infections.

For individuals with known allergies to tick saliva or a history of Lyme disease, consider prophylactic antibiotic therapy within 72 hours of removal, following current clinical guidelines. Regular self‑examination of the surrounding skin should continue, especially after outdoor activities in endemic areas.

Preventing Tick Bites and Associated Risks

Personal Protective Measures

Repellents and Clothing Choices

Effective prevention of tick attachment relies on chemical barriers and physical protection. Repellents containing DEET (20‑30 %), picaridin (20 %), or IR3535 (20 %) maintain efficacy for up to eight hours on exposed skin. Permethrin‑treated garments provide long‑lasting protection; a single application of 0.5 % permethrin remains active through multiple wash cycles. When selecting a repellent, prioritize products with proven tick‑specific testing and verify expiration dates to ensure potency.

Clothing choices reduce the likelihood of tick bites and the resulting erythematous lesions. Recommended practices include:

Wearing long sleeves and long trousers made of tightly woven fabric (minimum 600 D denier).
Tucking shirts into pants and securing pant legs with elastic cuffs or gaiters.
Selecting light‑colored garments to facilitate early tick detection.
Applying permethrin spray to all outerwear, hats, and shoes, following label instructions.

Combining a certified repellent with appropriate attire creates a dual barrier that minimizes tick contact, limits skin puncture events, and prevents the characteristic circular rash that can develop after attachment. Regular inspection of clothing and body surfaces after outdoor exposure remains essential for early removal of any attached arthropods.

Regular Skin Checks

Regular skin examinations are essential for early identification of tick attachment and the skin changes it produces. Prompt detection reduces the risk of pathogen transmission and limits tissue damage.

Examinations should occur after outdoor activities in tick‑infested areas, at least once a week during peak seasons, and immediately if a bite is suspected. Comprehensive checks include the scalp, behind ears, underarms, groin, and any concealed skin folds.

Key visual indicators of tick attachment:

Small, raised red papule at the bite site
Central puncture mark or dark spot where the mouthparts entered
Expanding erythema with a clear center (often described as a “target” or “bullseye”)
Localized swelling or tenderness

When any of these signs appear, remove the tick with fine‑tipped tweezers, grasping close to the skin and pulling straight upward. Clean the area with antiseptic, document the lesion, and monitor for progression over 24‑48 hours. Persistent or worsening symptoms warrant medical evaluation.

Environmental Controls

Landscaping and Yard Maintenance

Landscaping and yard maintenance directly influence the likelihood of human contact with ticks and the visibility of their bite marks. Dense, unmanaged vegetation provides shelter for ticks, increasing the probability that a person walking through the area will encounter an attached insect. Regular mowing, trimming, and removal of leaf litter reduce the microhabitat where ticks thrive, thereby lowering exposure risk.

Ticks attach to the skin for several days, during which they inject saliva that may cause a localized reaction. The bite site typically appears as a small, red papule surrounded by a faint halo. In many cases, a concentric ring—often called a “bull’s-eye”—develops as the infection progresses. The central puncture may be difficult to see, while the surrounding erythema expands over hours to days.

Effective yard management practices that also aid in early detection of tick bites include:

Keep grass at a maximum height of 4 inches; shorter blades limit tick movement.
Clear tall shrubs and brush around the perimeter of the property.
Create a barrier of wood chips or gravel between lawns and wooded areas.
Remove leaf piles and compost debris regularly.
Conduct weekly visual inspections of high‑traffic zones for ticks and skin lesions on occupants.

By maintaining a tidy landscape, homeowners minimize tick habitats and improve the chances of recognizing the subtle skin changes that indicate a recent bite. This proactive approach reduces the incidence of tick‑borne diseases and supports overall public health.

Pet Protection

Ticks that feed on dogs or cats often become vectors for pathogens that affect people. When a tick detaches from a pet and later bites a human, the bite site typically presents as a tiny, firm, red bump with a dark central point where the mouthparts remain embedded. Within hours the lesion may enlarge, develop a clear halo, or evolve into a rash resembling a target. In some cases, a slow‑growing ulcer or necrotic patch appears, indicating possible infection.

Pet owners can mitigate these risks by maintaining strict tick control. Regularly examine the animal’s coat, especially around ears, neck, and groin, for small, oval parasites. Prompt removal with fine‑tipped tweezers reduces the chance of pathogen transmission. Apply veterinarian‑approved acaricides according to label instructions; rotate products annually to prevent resistance. Keep the living environment clean—mow lawns, remove leaf litter, and treat outdoor areas with appropriate repellents.

Key protective measures:

Monthly topical or oral tick preventatives.
Routine grooming sessions that include tick checks.
Use of tick‑inhibiting collars for continuous coverage.
Environmental treatments in yards and kennels.
Immediate veterinary consultation if a tick is found attached for more than 24 hours.

Early identification of characteristic skin lesions on humans, combined with diligent pet protection, limits the spread of tick‑borne diseases and safeguards both animal and public health.