bubble_chart Overview

This disease is prevalent in forested areas of southern provinces in China, such as Fujian, Guangdong, Hubei, Hunan, and Zhejiang. It often breaks out regionally during the summer and autumn seasons, particularly from April to August when pine leaf insects are most active. According to surveys, approximately 40 species of pine leaf insects have been identified in China, with six being particularly harmful and widely distributed: the red pine leaf insect, the oil pine leaf insect, the deciduous pine leaf insect, the Masson pine leaf insect, the Yunnan pine leaf insect, and the Sia pine leaf insect. Among these, the Masson pine leaf insect has the widest distribution and causes the most significant damage.

bubble_chart Etiology

Pine leaf arthropathy refers to bone and joint lesions caused by direct or indirect contact with live or dead pine leaf insects or their hairs, which is part of a systemic disease.

Pine leaf insects generally have six instar stages. The 1st to 2nd instar pine leaf insects have not yet developed toxic hairs, while the 3rd to 4th instar ones have underdeveloped toxic hairs. The 5th to 6th instar pine leaf insects have highly developed toxic hairs and venom gland cells, making them the pathogenic stage. At this stage, the thoracic segments of the pine leaf insect possess well-developed hollow toxic hairs, each with a venom gland cell at its base that secretes venom into the hair cavity. When the pine leaf insect reaches adulthood, the toxic hairs stand erect outside its shell, so the cocoon also has a highly pathogenic nature. Even dead insects falling to the ground or into water can easily cause disease.

During the peak season of pine leaf insects, activities such as cutting firewood, harvesting grass in infested areas, or working in contaminated rice paddies can lead to contact with live or dead pine leaf insects, their toxic hairs, or contaminated clothing, firewood, grass, or water, all of which can cause the disease. Epidemiological surveys and animal experiments have confirmed this, hence the name "pine leaf insect disease." The toxins secreted by the toxic hairs and venom gland cells of the pine leaf insect enter the human body upon contact with the skin, triggering an allergic-type immune inflammatory response that primarily affects the skin and joints, and sometimes the eyes or auricles.

The pathogenesis remains unclear. Some scholars believe it is caused by toxins entering the bloodstream after the toxic hairs pierce the skin, leading to toxemia, but animal experiments have not confirmed this. Since anti-allergy medications can rapidly control symptoms in the early stages of the disease, some scholars hypothesize that the mechanism is an allergic reaction, though this has also not been strongly substantiated. Others suggest an infectious cause, as purulent fluid extracted from affected joints or skin nodules has been cultured to reveal Staphylococcus aureus, Staphylococcus albus, or Pseudomonas aeruginosa. The pathological manifestations align with low-toxicity infections, but most cultures of locally extracted fluids are negative. None of the above views have provided a clear explanation of the disease's pathogenesis, which awaits further research.

bubble_chart Pathological Changes

The pathological changes in bones and joints in this disease manifest as aseptic inflammation. The affected bones and joints first exhibit reactive edema and congestion, with a small amount of bloody, viscous exudate on the synovial membrane, which appears rough without obvious inflammatory cell infiltration. As the disease progresses, the synovial membrane thickens significantly, sometimes up to several centimeters, adhering to the surrounding thickened connective tissue and showing inflammatory cell infiltration. If the thickening of the synovial membrane and soft tissues continues to worsen, it can compress the local skin, impair blood supply, leading to necrosis and the formation of a sinus. Additionally, due to the rough articular cartilage surface and insufficient blood supply, subchondral bone destruction may be filled with granulation tissue. The joint space narrows, the periosteum thickens, resulting in fibrous or bony ankylosis.

bubble_chart Clinical Manifestations

The disease often suddenly manifests at night within two days after exposure, though onset may be delayed up to 15–30 days. It is characterized by mild systemic symptoms but severe local manifestations. Systemic symptoms may be absent or mild, occasionally including fear of cold, poor appetite, dizziness, headache, general lack of strength, or a fever below 38°C, rarely reaching 39°C, typically improving or subsiding within 2–3 days. Regional lymph nodes may swell, gradually subsiding over about half a month, usually without ulceration.

Local symptoms appear on exposed body parts, commonly the hands, wrists, feet, or ankles. When joints are affected, acute-phase symptoms include joint swelling, localized redness, pain, elevated skin temperature, and impaired function. The pain is severe, persistent, stabbing, and paroxysmally worsening, particularly at night, making sleep difficult. Redness and swelling may recur, often affecting a single joint, though about one-third of cases involve multiple joints. Symptoms may also shift from one joint to another. Most patients develop a 1–2 cm red halo around the affected area, with a painful nodular mass at the center. In some cases, the swollen nodule may feel fluctuant, yielding viscous bloody fluid upon puncture, with no bacterial growth in cultures. Chronic cases may lead to gradual stiffness; a few patients develop persistent sinuses or fistulas, or even suppurative arthritis.

When joints are affected, various skin manifestations may also occur, such as macules, papules, wheals, vesicles, pustules, subcutaneous nodules, hematomas, or red swellings. These typically resolve within a week of treatment, though some may persist for months as chronic dermatitis. Other possible complications include scleritis, acute iridocyclitis, or auricle inflammation. Sometimes, severely painful soft tissue masses develop, gradually enlarging over 15–30 days before softening, with a病程 of 1–3 months.

Pine leaf虫-induced arthropathy has a high incidence and severe consequences, often causing lasting functional impairment or even disability, with some cases lasting 1–2 years.

The above clinical manifestations may occur alone or coexist in the same patient, though osteoarthritis is the most common, accounting for 30–90% of cases.

bubble_chart Auxiliary Examination

Over 60% of patients exhibit eosinophilia in their blood tests, while 50–60% have a total white blood cell count exceeding 10,000/mm³. Elevated erythrocyte sedimentation rates are observed in approximately 40–70% of cases. Soft tissue masses or joint aspirates often yield a pale yellow or greenish-yellow viscous gelatinous fluid, occasionally tinged with blood. Bacterial cultures are mostly negative, though a minority may show growth of Staphylococcus aureus, Staphylococcus albus, or Pseudomonas aeruginosa.

X-ray findings: In the acute phase, results are typically negative, with most cases showing bone changes about one month after onset. Around 12 days into the illness, X-rays may reveal soft tissue swelling, increased density around joints, reduced transparency of subcutaneous fat, and joint capsule enlargement. Later, a few cases may display calcification or ossification in adjacent soft tissues. Early-stage osteoporosis is followed by blurred bone margins with moth-eaten destruction, commonly seen in bony prominences where tendons and ligaments attach, such as the femoral trochanter, olecranon, and radial styloid. Most cases exhibit a single-layer fine linear periosteal reaction in the bone destruction zones, sometimes appearing as spur-like or lace-like formations.

Chronic changes primarily involve sclerotic hyperplasia around small bone destruction areas, forming well-defined, hardened small circular lesions. Involvement of small tubular bones manifests as thickening of the entire shaft. If the epiphysis or metaphysis is damaged, it may affect the epiphyseal line, leading to premature epiphyseal fusion. No evidence of sequestrum formation is observed in bone changes.

Joint alterations, aside from early swelling shadows and osteoporosis, include asymmetric joint space narrowing, uneven and deformed cartilage surfaces, and occasional subluxation. Subchondral bone destruction is often present. Chronic changes mainly involve bone hyperplasia and sclerosis, with potential spontaneous joint fusion leading to ankylosis.

bubble_chart Treatment Measures

The principle of combining prevention and treatment is very important. First, there should be an intelligence system for pine leaf insects to detect and actively eliminate them in a timely manner. Temporarily prohibit labor in forest areas where large numbers of pine leaf insects have already occurred. If exposed to pine leaf insects or their contaminants, immediately wash the exposed areas with soapy water, bleach solution, 5% urea solution, or alkali water made from soaking stove ash. Apply iodine or ammonia water to itchy areas, and check for the presence of toxic hairs. Seek immediate medical attention if any abnormalities occur.

Treatment should combine the removal of toxic hairs with medication. For systemic or localized itching, intravenous injection of 10% calcium gluconate can be used, along with oral antihistamines such as chlorpheniramine. For local lesions, 0.5–1% procaine mixed with prednisolone can be injected around the lesion for local blockade, or the blockade can be combined with external application of centipede, Dahurian Angelica, and egg white once a day, alongside antihistamines, pain relievers, and anti-inflammatory drugs. Ensure that affected joints are kept in a functional position with braces. Generally, with early and timely treatment, full recovery can be achieved in about a month. However, in some cases, after prolonged non-surgical treatment, acute symptoms may significantly improve, but joint pain, swelling, deformation, sinus or fistula formation, joint stiffness, and loss of labor capacity may persist. Depending on the condition, procedures such as lesion debridement, synovial membrane resection, osteotomy for deformity correction, joint fusion, or artificial joint replacement may be performed. After recovery, the condition generally does not recur.