With the development of the world economy and the improvement of people's living standards, both developed and developing countries have set off a pet craze. In recent ten years, the pet industry has developed rapidly in China, and dogs, cats, fish and birds have entered people's families. Keeping pets, especially dogs and cats that are closest to people, not only adds fun to people's lives, but also poses a threat to human health. It has brought unprecedented business opportunities to the pet market, and also brought severe challenges to the prevention and treatment of parasitic diseases in humans and animals. Therefore, this paper summarizes the research status of CPCMA and its application in pet (dog, cat) vaccine control.
1 Pets (dogs, cats) People and animals * * * suffer from parasitic diseases.
1. 1 main species According to literature retrieval, there are at least 39 kinds of parasitic diseases in dogs, cats, humans and animals, accounting for about 56% of CPCMA. Among them, there are 9 species of protozoa (visceral leishmaniasis, cutaneous leishmaniasis, cutaneous leishmaniasis, pulmonary cysticercosis, toxoplasmosis, African trypanosomiasis, Creutzfeldt-Jakob disease, isosporidiosis and Giardia) and 8 species of trematodes (schistosomiasis, clonorchiasis, posthumous clonorchiasis, double cavity trematode, echinococcosis, Fasciolopsiasis and heterotypia). Echinococcosis, sparganosis, schizophrenia, echinococcosis, cysticercosis), 10 kinds of nematodiasis (hookworm disease, swollen nematode disease, capillary nematode disease, guinea worm disease, canine filariasis, Malay filariasis, sucking nematode disease, jaw nematode disease, roundworm disease, trichinosis), and echinococcosis.
1.2 life history type [2]
1.2. 1 Direct pathogenic organisms are directly transmitted to susceptible vertebrates or humans through contact or media, and the pathogens do not develop and reproduce during the transmission process. Such as scabies and demodicidosis, are called direct zoonosis.
1.2.2 The cycle life cycle needs more than one vertebrate host. Such as taeniasis and echinococcosis. It is called circulatory zoonosis.
1.2.3 vector-borne pathogens develop and reproduce in the medium, or both, and then spread to vertebrates or humans. Such as malaria and filariasis. It is called vector human-animal disease.
1.2.4 pollution exists in the non-animal environment where vertebrate hosts and pathogens develop or store, such as water, food, soil and plants. The infection of the host comes from the polluted non-animal environment. Such as hookworm disease, fecal ascariasis and so on. This is called polluting humans and animals.
1.3 epidemic factors
1.3. 1 The source of infection is wide, and the host selection of human and animal parasites is not strict, and one parasite can be parasitic on multiple hosts. Besides people, dogs and cats, there are many kinds of wild animals such as mammals, birds, birds, fish and reptiles. The infected host is an important source of infection, and the universality of infection source is the main reason why CPCMA is widely distributed and difficult to control.
1.3.2 The spread and prevalence of multi-transmission CPCMA is a process in which people and animals * * * participate in the movement of parasite population in the ecosystem. Transmission routes include animal to animal, human to animal, animal to animal and human to animal. Various popular links are independent, interrelated, influential and restrictive. There are also various infection modes, including oral cavity, skin or mucous membrane, contact, droplets, placenta, arthropod transmission and other congenital and acquired infection modes.
1.3.3 The immunity of susceptible parasites infected hosts is mostly non-elimination immunity, and uninfected hosts are susceptible due to lack of specific immunity. When the parasites in the infected host with immunity are eliminated, this specific acquired immunity will gradually disappear, become susceptible again and be susceptible to reinfection. Susceptibility to some parasites is not only related to immunity, but also related to the eating habits and living habits of the host.
1.4 principles of prevention and control The prevention and control of CPCMA often formulates corresponding laws, regulations and supervision and management systems according to the epidemic situation and epidemic law, organically combines controlling the source of infection, cutting off the transmission route and protecting susceptible hosts, and takes measures according to local conditions, giving priority to prevention and comprehensive management. Immunoprophylaxis is to prevent and treat parasitic diseases by inducing host to produce specific immunity through vaccination. It is considered by scientists at home and abroad as the safest and most effective prevention and control measure, and it is also the goal that people have been pursuing for many years.
2. Research on parasite vaccines for pets (dogs, cats), humans and animals.
2. 1 current situation and demand for a long time, the prevention and treatment of parasitic diseases of people and animals has been mainly based on drug deworming, and remarkable results have been achieved. In the past 10 years, anthelmintics have become the fastest growing field in the animal medicine market, accounting for about a quarter of the world's animal medicine sales (18 trillion US dollars) [4]. So far, drug deworming still plays an important role in the treatment and control of parasitic diseases. However, the long-term large-scale application of chemical drugs has led to drug-resistant parasites, chemical drug residues and food safety and environmental pollution caused by drug residues [5]. In addition, the obvious reinfection of parasites, the long development cycle of new anti-insect drugs, the huge investment and the desire and demand of pet owners for vaccine prevention have aroused great concern from researchers and businesses. The new field of parasite vaccine control is quietly emerging, and a potential and huge pet parasite vaccine commodity market will face competition.
2.2 Progress in vaccine research Because vaccines are safe, have no side effects, no residues, no pollution, have dual functions of prevention and treatment, and are easily accepted by consumers, human beings have put forward requirements for vaccine prevention and treatment of almost all infectious diseases. Although the parasite's structure, complex antigen, parasitic site and special immune mechanism have brought many difficulties to vaccine research and development, the demand for health and safety of consumers and the demand for vaccines in the pet market with a profit of more than $3 trillion have brought great impetus to the research of parasite vaccines. Although remarkable progress has been made in the research of veterinary parasite vaccines, most commercial parasite vaccines are still live vaccines or attenuated live vaccines. Due to the problems of low protection rate, poor safety, low output and high cost, the commercialization prospect is not optimistic (Bain, 1999) [6]. The research of genetic engineering vaccine and nucleic acid vaccine can make the industrialization and commercialization of parasite vaccine a reality, and many scientists have great expectations for it (Alarcon et al., 1999) [7].
2.2. 1 Protozoan vaccine is an important pathogen causing CPCMA. In the field of medical research, people have accumulated a lot of knowledge of immunology, genomics and vaccinology in the research of plasmodium, Toxoplasma gondii, Leishmania and trypanosoma, and used these knowledge to develop Giardia vaccine, Toxoplasma gondii vaccine, Cryptosporidium vaccine and coccidia vaccine for the prevention and treatment of animal parasitic diseases. At present, several vaccines have been marketed (Olson et al., 2000; Augstine, 2001) [8,9] The research of Leishmania vaccine has gone through the process of whole worm vaccine, recombination vaccines vaccine and nucleic acid vaccine. In 1999, it was confirmed that LPG (lipopolysaccharide) is a promising candidate vaccine to block transmission. At present, the protective antigen genes of Leishmania major nucleic acid vaccines include surface antigen gp63, LACK, PSA-2, surface antigen /gp46/M-2 and so on. Handman et al. (200 1) found that DNA vaccine also has therapeutic effect [10], Mendez et al. (200 1) studied the immunity of C57BL/6 mice with L. major, and the results showed that DNA vaccination could produce effective protection [1/kloc-]. In addition, a kind of LACK protein with high protection rate was found. After constructing the vaccine of Leishmania magna LACK DNA [12], it was confirmed that it could induce Th 1 reaction and control infection.
Giardia vaccine developed by the Animal Health Organization of Fort Dodge (1999) can reduce or prevent Giardia cysts in the intestines of dogs and cats, and finally realize the infection without trophozoites in vaccinated animals (Olson et al., 2000) [13]. 1993, Interway Company developed Toxoplasma DNA vaccine "Toxovax" with S48 strain of Toxoplasma gondii, which has achieved effective results in preventing toxoplasmosis in sheep. As for the study of nucleic acid vaccine of Toxoplasma gondii, Angus et al. (1996) made a preliminary study on immunizing mice with SAGI heavy plasmid of Toxoplasma gondii. Zhou Yong An et al. (1999) immunized mice with PcDNA3-p30 eukaryotic expression plasmid, and the results showed that the serum antibody increased and the survival time of infected mice was prolonged [14]. Guo Hong et al. (1999) used IFN-γ as adjuvant to immunize mice. The results showed that NK cell activity and CD8+T cells increased significantly, and CD4+/CD8+ ratio decreased significantly [15]. Recombination vaccines is studying the prevention of coccidiosis, and the study of immune response induced by coccidiosis antigen EalA expressed by Salmonella is also in the experiment (Song et al., 2000) [16]. Many experimental studies show that the protective immunity against protozoan infection can be established artificially.
2.2.2 trematode vaccine Human trematodes have vertebrate hosts, and most of them can spread naturally between humans and vertebrates. At present, the research on its vaccine is mainly found in Schistosoma japonicum and Fasciola. Schistosoma vaccine research has also experienced the development process from whole worm vaccine (dead vaccine, live vaccine, homologous attenuated live vaccine, heterogeneous live vaccine) to molecular vaccine (genetic engineering subunit vaccine, synthetic peptide vaccine, nucleic acid vaccine). With the development of high-tech biotechnology, candidate antigen molecules or antigen genes of Schistosoma japonicum vaccine have been continuously discovered and identified, and genetic engineering vaccine has become the main research direction. During the period of 1998, WHO /TDR conducted parallel experiments on several candidate molecules of Schistosoma mansoni (Sm) vaccine in two independent laboratories, and put forward six potential vaccine candidate molecules, including 28kDa SmGST (glutathione -S- transferase), 97 kDa ASM paramyosin (paramyosin) and IrV-5 (antigen molecule screened by attenuated cercariae immune serum). Among them, GST has entered clinical trials, paramyosin, MAP-4/TPI and Sm 14 antigens will be prepared according to GMP standards for clinical trials, while IrV-5 and MAP-3/Sm23 suggest to continue the research in the form of DNA immunization [2].
1999 It is reported that cathepsins L 1 and L2 secreted by Fasciola hepatica are important protein molecules involved in immune escape, tissue penetration and nutrient absorption (Mulcahy et al.,1999; Spithill et al., 1999) [17, 18]. Inoculating it to cattle can reduce the insect population by 42% ~ 69% and the egg activity by 60%. If combined with high molecular hemoglobin, the protection rate can be increased to 73%(McGonigle et al., 1995). Piacenza et al. (1999) inoculated it into sheep, the protection rate was 60%, and the egg reduction rate was 7 1% ~ 8 1%. When it is combined with natural leucine aminopeptidase, the protection rate can be increased to 79% [19]. The protective rates of other protein molecules of Fasciola hepatica, such as glutathione S transferase (GST) and fatty acid binding protein (FABP), to cattle were 65,438+09% ~ 67% and 55% respectively, but Fasciola hepatica was not reported in recombination vaccines (Spithill et al., 65,438+0999) [20].
2.2.3 Taenia tapeworm vaccine can also cause human and animal diseases, and cysticercosis and echinococcosis caused by parasitic larvae of Taenia tapeworm in the middle stage are more harmful to the host. The research on prevention of tapeworm (cysticercosis) and echinococcosis (echinococcosis) in recombination vaccines has been successful. In 1980s, the experimental results in China, New Zealand, Australia and Argentina showed that the protective rate of Echinococcus vaccine EG95 against bovine infection was 96% ~ 100%. The protection rate of 45W vaccine against Taenia solium infection in sheep is over 92%, and Taenia solium vaccine is also effective in preventing infection in cattle. EG95 and 45W antigens are expressed on the surface of Hexagonal Insects, which combine with antibodies and complements to prevent Hexagonal Insects from escaping and migrating, thus playing a protective immune role. Another important feature is that it can produce cross-species protection. It has been proved that the complex of Taenia solium 45W and To 18t to 16 molecules can induce artificial infection in pigs, and the protection rate is 93%. Therefore, it has potential application in preventing human infection (Lightowlers et al., 2000) [2 1]. Chabalgoity(200 1) reported that the weak expression form of Salmonella typhimurium (LVRO 1) in Echinococcus fatty acid binding protein can produce effective humoral and cellular immune responses, and the author suggested that this expression form should be used when studying other candidate vaccines for dogs, because the expression form of Salmonella typhimurium LCRO 1 is harmless to dogs [22].
2.2.4 Nematode Vaccine The research goal of hookworm vaccine is mainly aimed at reducing insect load, reducing host blood loss and enhancing cross-defense. As early as 1930s, the Department of Entomology, School of Public Health, Johns Hopkins University, USA, used live leptospira canis tertiary larvae (L3) to inoculate dogs and rats orally or subcutaneously, which could reduce the worm population and intestinal bleeding. In 1960s, L3 vaccine was developed into live attenuated vaccine and put on the market in early 1970s. But it was eliminated because it could not resist infection and reinfection and was expensive. Subsequently, the research focus turned to L3 secreted protein (ASP). At present, similar proteins of ASP- 1 and ASP-2 have been isolated and cloned from Leptospira duodenale, Leptospira Ceylon and Leptospira americana. And there is evidence that ASP is a promising vaccine antigen [23].
Gastrointestinal nematodes of Haemophilus, Oster and Tricholoma are the most important parasites of cattle, sheep and other animals, occupying the largest share in the market of anthelmintics, and people have invested the most research energy. The effective nematode vaccine is110 kda h11protein molecule with aminopeptidase A and M activities. The expression of H 1 1 binding antibody on the microvilli of nematodes can destroy the feeding ability of larvae and adults in the fourth stage of nematodes, and the protection rate for lambs is over 90%. This protection rate is related to antibody titer. Because H 1 1 has no immunogenicity in natural infection, it is considered as a "hidden antigen" (Newton et al., 1999) [24]. The results showed that the protection rate of Haemophilus contortus p 100GA 1 was 60% and the reduction rate was 50% in preventing goat heterologous infection. Extracting a single molecule, or at least several molecules, which can produce cross protection from many vaccine components has become the focus of nematode vaccine research. And "hidden antigen" is considered as the most ideal candidate. Another challenge is to industrialize vaccine research through recombinant DNA and other technologies, and the research on recombinant H1,H-gal-GP and TSBP is developing in this direction (Knox et al., 200 1) [25].
2.2.5 At present, the research on arthropod vaccines mainly focuses on arthropods (ticks, mites, bloodsucking flies, lice, etc. ) is related to economic animals such as cattle and sheep. The most landmark is the genetically engineered vaccine [tick gard TM] expressed by Escherichia coli, which was jointly developed by Australian Institute of Biotechnology and CSIRO to prevent ticks [26]. Since then, a similar recombination vaccines [gavac TM] has been successfully expressed in yeast and commercialized by Heber Institute of Biotechnology in Havana, Cuba (Garcia et al., 2000) [27]. The antibody induced by this vaccine can bind and dissolve Bm86 molecules on tick intestinal cells, thus interfering with the blood-sucking behavior of ticks and reducing their reproductive ability. From 65438 to 0999, the Australian Institute of Biotechnology developed the second generation [Tickgard Plus (TM)] vaccine, which can produce a strong and lasting immune response. In the same year, the Canadian protease "hypodermin A" for preventing dermatophagoides farinae was approved to be listed in recombination vaccines (Pruett, 1999) [28].
2.3 Prospect of parasite vaccine research The above evidence shows that there are many kinds of CPCMA, and the epidemic factors are complex, so it is difficult to prevent and control it. People are trying to find a new way to effectively prevent and eliminate this disease. A large number of research results have proved that it is feasible to induce the host to produce protective immunity by vaccination and prevent parasites and arthropods from infecting or invading the host. Although great progress has been made in the study of candidate antigens of various parasite vaccines, the immune protection rate induced by most vaccines is not satisfactory. Antigen isolation and screening, gene cloning and recombination, efficient expression, improving protection rate and cross-protection are still the focus of future research. Of course, the process of research and commercialization of parasite vaccine preparation is not overnight, it involves many links such as parasite biology, molecular biology, immunology, vaccine experiment, industrialization and commercialization. We believe that with the application and development of modern high and new technologies such as immunology, genomics and molecular biology in the field of parasitology, parasite vaccine will play an important role in the prevention and control of CPCMA.