Distal lung tumor
Nematodes westermani
Mesoderm westermani nematodes
Paragonimus lindleyi
Paragonimus westermani
Paragonimus westermani [Kerbert, 1878) Braun, 1899] is the main pathogen of human paragonimiasis, and it is also the earliest discovered paragonimiasis. Cyst formation in the lungs is the main pathological change, and the main symptoms are rotten peach-like blood sputum and hemoptysis.
Paragonimus westermani is oval in shape, thick in body, slightly raised in back and flat in ventral surface. Life is reddish-brown, and its shape is constantly changing. Under the light microscope, it can be seen that there are tiny prickles on the fixed worms, most of which are arranged in solitary form, and occasionally clustered and mixed. The oral sucker is about the same size as the abdominal sucker. The oral sucker is located at the front end of the worm, and the abdominal sucker is located in the middle of the worm's ventral surface. The digestive organs include the mouth, pharynx, esophagus and two curved intestinal branches. The oral cavity is connected with the muscular pharyngeal bulb, and the esophagus is short. Two curved intestinal branches extend to the back of the worm and end in the blind end. The ovary has six leaves, which are juxtaposed with the uterus behind the abdominal sucker, and two testicular branches, such as fingers, are juxtaposed behind the worm 1/3. Ovarian morphology, the ratio of oral sucker to abdominal sucker and the ratio of testicular length are important characteristics of morphological identification of Paragonimus.
Figure 1 adult Paragonimus westermani
The egg is golden yellow and oval, with the size of 80 ~ 1 18× 48 ~ 60μ m, with a slightly protruding front end, a flat egg cover and a slightly narrow back end. The eggshell is uneven in thickness, and the back end is often thickened. The egg contains 1 egg and more than 10 yolk cells. The covers of several eggs are not easy to see.
4 Life History of Paragonimus westermani The ultimate hosts of Paragonimus westermani include humans and many carnivorous mammals. The first intermediate host is some snails of the family Spiridae and Pleurotus, and the second intermediate host is freshwater crabs or crustacean crickets. The life history process includes egg, metacercaria, metacercaria, mother cercaria, daughter cercaria, cercaria, metacercaria, child worm and adult stage.
Fig. 2 Life history of Paragonimus westermani
Adults are parasitic in the lungs. Because the formed cysts communicate with the bronchi, eggs can be excreted through the trachea or swallowed with sputum and excreted with feces. When eggs enter the water, they hatch in about 3 weeks at the right temperature. When they meet the first intermediate host freshwater snail, they actively invade and develop into cercaria through cercaria, mother cercaria and daughter cercaria. Mature cercaria has a short tail and uses two suckers for inchworm movement. Actively invade in water or be swallowed by crabs and shrews, forming cysts in these second intermediate hosts. Cysticercosis is spherical with two walls, and the outer layer is about 300 ~ 400 microns in diameter. People or other end hosts are infected by eating crabs and crickets containing live metacercariae.
After the metacercariae enters the digestive tract of the final host, it takes about 30 to 60 minutes for the metacercariae to come out of the cyst under the action of digestive juice at the front end of the small intestine. With the help of the strong telescopic movement of two suction cups and the secretion of the front gland, it drills into the intestinal wall, which is a child worm. Children's worms move in tissues and wander between organs and abdominal cavity. 1~3 weeks later, it enters the chest cavity and lungs from the surface of the liver or through the liver or directly from the abdominal cavity through the diaphragm, and finally matures and lays eggs in the lungs. Some larvae can shuttle between host tissues for a lifetime until they die. It usually takes more than 2 months from the entry of metacercariae into the final host to mature spawning. Adults can live for 5 to 6 years in the host, and the elderly can live for 20 years.
Pathogenicity of Paragonimus westermani The pathogenicity of Paragonimus westermani is mainly caused by the migration, disturbance and adult settlement of larvae in tissues and organs. The incubation period of the disease ranges from 2~ 15 days, and that of the elderly is 1~3 months. Pathological process can generally be divided into acute stage and chronic stage.
5. The acute phase of1is mainly caused by the migration of larvae. After degloving, cercariae pass through intestinal mucosa to form hemorrhagic or suppurative sinus. If a child worm enters the abdominal cavity, it can cause turbid or bloody effusion, which contains a large number of eosinophils. Worms entering the abdominal wall can cause hemorrhagic or suppurative myositis. When invading the liver, fibrin is attached to the place where it passes, and the surface of the liver looks like "moth-eaten". If a worm passes through the liver, the surface looks like a needle-like stomata. Sometimes the liver has cirrhosis locally. If the worm passes through the diaphragm and spleen, it can also form punctate bleeding and inflammation. The symptoms in the acute stage mostly appear from a few days to 1 month after eating metacercariae, and some of them appear the next day.
Symptoms in the acute stage are different, and the mild ones only show general symptoms such as loss of appetite, fatigue, abdominal pain, diarrhea and low fever. In severe cases, systemic allergic reaction, high fever, abdominal pain, chest pain, cough, shortness of breath, hepatomegaly with urticaria may occur. Leukocytosis, eosinophils increased significantly, generally 20%~40%, the highest can reach more than 80%.
5.2 Pathological changes caused by insects entering the lung in chronic stage can be roughly divided into three stages:
(1) Abscess stage? It is mainly caused by insect migration, such as tissue destruction, bleeding, secondary infection and so on. Visible to the naked eye, the lesion is cave-like or tunnel-like, with blood and inflammatory exudation, and then granulation tissue is around the lesion, forming a membrane capsule wall.
(2) Cystic stage? Due to exudative inflammation, a large number of cells infiltrated, aggregated, died, disintegrated and liquefied, and the abscess was filled with reddish-brown jam-like liquid. Microscopic examination showed necrotic tissue, Charcot crystals and a large number of eggs. The epithelium of the cyst wall itself is the bronchiolar epithelium of the host, so some people think that the cyst is caused by bronchiectasis and inflammatory thickening caused by insects digging holes.
(3) Fibrous scar period? Due to the death or transfer of the worm to other places, the contents of the cyst are discharged or absorbed through the bronchus, and the cyst is full of granulation tissue, fibrosis and finally scar formation.
The above three stages can exist in the same organ at the same time because worms move in different tissues before and after.
In the chronic stage, due to the damage of multiple organs, and the degree of damage is different, the clinical manifestations are more complicated. Clinically, according to organ damage, it can be mainly divided into:
Thoracopulmonary type
The most common symptoms are cough, chest pain, coughing up jam-like or rust-colored blood sputum. Eggs can be found in blood sputum. When worms are disturbed in the chest cavity, they can invade the pleura, causing exudative pleurisy, pleural effusion, pleural adhesion, pericarditis, pericardial effusion and so on.
Abdominal type
In about13 cases, the worm passed through the intestinal wall and swam between the abdominal cavity and various organs, resulting in abdominal pain, diarrhea, bloody stool and other symptoms. Abdominal pain is not fixed, mostly dull pain. It can also cause extensive inflammation and adhesion of abdominal organs, and occasionally peritonitis and ascites. Especially when worms invade the liver, it will cause liver damage or liver enlargement.
Subcutaneous mass type
About 10% cases may have subcutaneous masses. Bags vary in size, mostly 1~3cm. The surface skin is normal, and the mass is palpable, often in a single distribution, and occasionally multiple strings can be seen. After the mass disappears, it reappears in the vicinity or other parts at regular intervals. The common parts are abdominal wall, chest and back, head and neck. Almost all human body surfaces have the possibility of lumps everywhere. Some subcutaneous masses caused by Paragonimus westermani are migratory and some are not, and sometimes adults and eggs can be detected in the masses.
Cerebrospinal type
About 10%~20% cases, most of them are teenagers, often accompanied by lung or other lesions. Worm migration or settlement in cysts can lead to brain and spinal cord injury. Insects destroy brain tissue, early exudative inflammation, then edema, and then cyst formation. Due to the migration of insects, many injuries are caused, so the location and scope of lesions are changeable and the symptoms are complex, which is often difficult to explain with one lesion. Patients often have paroxysmal severe headache, hysteria, epilepsy and paralysis. It can also manifest as intracranial space occupying lesions, meningitis, optic nerve injury, subarachnoid hemorrhage and other symptoms. If worms invade the spinal cord, the main manifestations are spinal cord compression, lower limb movement or sensory disturbance, and even paraplegia.
Subclinical type
In epidemic areas, some patients are positive in skin test and serum immunological test, and eosinophils increase, sometimes accompanied by liver function damage. X-ray chest film can have typical changes, but there are no obvious symptoms. This kind of patients may be slightly infected, or infected at the initial stage of infection or the worm has disappeared.
Other types
Because almost all organs of the human body can be violated, there are other types of damage besides the above-mentioned common types. Some patients can have multiple types of damage at the same time or successively, and the above classification is only convenient for clinical treatment.
6. Diagnosis of Paragonimus westermani 6. 1 Diagnosis of pathogens Only when eggs are found in sputum or feces and worms are found in excised subcutaneous masses can a diagnosis be made.
Mild patients should be treated with 10% sodium hydroxide solution for 24 hours and then centrifuged for microscopic examination.
6.2 Immunological tests are often screened by intradermal tests in general surveys, but the false positives and false negatives are both high. ELISA is a widely used detection method because of its high sensitivity. In recent years, the detection of circulating antigen has also been studied and applied, which has the advantages of high sensitivity and curative effect evaluation.
6.3 X-ray and CT examination are suitable for patients with thoracic lung type and encephalomyelitis type.
7 Prevalence of Paragonimus westermani 7. 1 Distribution Paragonimus westermani is widely distributed in the world, and has been reported in Japan, South Korea, Russia, Philippines, Malaysia, India, Thailand, Africa and South America. In China, except Tibet, Xinjiang, Inner Mongolia, Qinghai and Ningxia, it has been reported in 26 provinces, municipalities and autonomous regions.
7.2 Types of epidemic areas According to the second intermediate host species, epidemic areas can be divided into two types: crab-type epidemic areas and mole-type epidemic areas, which only exist in the three northeastern provinces. At present, the characteristics of crab-type epidemic areas are that there are not many patients in the epidemic areas and they are distributed in spots. Once found, it is easy to control. Due to the local residents' special interest in Gryllotalpa and its products, although the number of patients in Gryllotalpa epidemic area has decreased obviously after years of efforts, it is still a frequently-occurring and common disease in some areas.
7.3 The sources of infection are people who can excrete eggs and carnivorous mammals. There are many kinds of hosts of this insect, such as tigers, leopards, wolves, foxes, leopard cats, civets and other wild animals, as well as domestic animals such as cats and dogs. In some areas, such as Kuandian County, Liaoning Province, dogs are the main source of infection. Infected wild animals are the main source of infection in natural foci.
7.4 Intermediate Hosts The first intermediate hosts are snails that live in fresh water in mountainous areas. The second intermediate host is freshwater crabs, such as Eriocheir sinensis, Eriocheir sinensis, Eriocheir sinensis and Eriocheir sinensis. And crabs in the northeast. It is reported that freshwater shrimp can also be used as an intermediate host. These first and second intermediate hosts live together in small rivers and streams in mountains and hills, so this disease is more common in hills or mountains. In recent years, there is a trend of urbanization.
7.5 Various animals, such as wild boar, pig, rabbit, mouse, frog, chicken, bird, etc. , has been proved to be a relay host. Large carnivores such as tigers and leopards are infected by preying on these relay hosts. Recurrent host is an important factor in epidemiology because of its variety, large quantity and wide distribution.
7.6 Mode of infection Residents in epidemic areas often have the habit of eating crabs and crickets raw or half-eaten. Cysticercosis in crabs or moles is not killed, which is the main cause of infection. After the death of the intermediate host, the metacercariae falls off from the water, and if the water containing metacercariae is eaten raw, it can also lead to infection.
8 Prevention and treatment of Paragonimus westermani The most effective way to prevent this disease is not to eat raw or half-eaten crabs, shrews and their products, and not to drink raw water. Health education is an important measure to control the epidemic of the disease.