Microsporidia are long-known parasitic organisms of almost every animal group, including invertebrates and vertebrates. Microsporidia emerged as important opportunistic pathogens in humans when AIDS became pandemic and, more recently, have also increasingly been detected in otherwise immunocompromised patients, including organ transplant recipients, and in immunocompetent persons with corneal infection or diarrhea. Two species causing rare infections in humans, Encephalitozoon cuniculi and Brachiola vesicularum, had previously been described from animal hosts (vertebrates and insects, respectively). However, several new microsporidial species, including Enterocytozoon bieneusi, the most prevalent human microsporidian causing human immunodeficiency virus-associated diarrhea, have been discovered in humans, raising the question of their natural origin. Vertebrate hosts are now identified for all four major microsporidial species infecting humans (E. bieneusi and the three Encephalitozoon spp.), implying a zoonotic nature of these parasites. Molecular studies have identified phenotypic and/or genetic variability within these species, indicating that they are not uniform, and have allowed the question of their zoonotic potential to be addressed. The focus of this review is the zoonotic potential of the various microsporidia and a brief update on other microsporidia which have no known host or an invertebrate host and which cause rare infections in humans.

http://lib.ajaums.ac.ir/booklist/clinical microbiology reviews-july.pdf

Zoonotic Potential of the Microsporidia

Humans are infected by four recognized species of malaria parasites. The last of these to be recognized and described is Plasmodium ovale. Like the other malaria parasites of primates, this parasite is only transmitted via the bites of infected Anopheles mosquitoes. The prepatent period in the human ranges from 12 to 20 days. Some forms in the liver have delayed development, and relapse may occur after periods of up to 4 years after infection. The developmental cycle in the blood lasts approximately 49 h. An examination of records from induced infections indicated that there were an average of 10.3 fever episodes of > or = 101 degrees F and 4.5 fever episodes of > or = 104 degrees F. Mean maximum parasite levels were 6,944/microl for sporozoite-induced infections and 7,310/microl for trophozoite-induced infections. Exoerythrocytic stages have been demonstrated in the liver of humans, chimpanzees, and Saimiri monkeys following injection of sporozoites. Many different Anopheles species have been shown to be susceptible to infection with P. ovale, including A. gambiae, A. atroparvus, A. dirus, A. freeborni, A. albimanus, A. quadrimaculatus, A. stephensi, A. maculatus, A. subpictus, and A. farauti. An enzyme-linked immunosorbent assay has been developed to detect mosquitoes infected with P. ovale using a monoclonal antibody directed against the circumsporozoite protein. Plasmodium ovale is primarily distributed throughout sub-Saharan Africa. It has also been reported from numerous islands in the western Pacific. In more recent years, there have been reports of its distribution on the Asian mainland. Whether or not it will become a major public health problem there remains to be seen. The diagnosis of P. ovale is based primarily on the characteristics of the blood stages and its differentiation from P. vivax. The sometimes elliptical shape of the infected erythrocyte is often diagnostic when combined with other, subtler differences in morphology. The advent of molecular techniques, primarily PCR, has made diagnostic confirmation possible. The development of techniques for the long-term frozen preservation of malaria parasites has allowed the development diagnostic reference standards for P. ovale. Infections in chimpanzees are used to provide reference and diagnostic material for serologic and molecular studies because this parasite has not been shown to develop in other nonhuman primates, nor has it adapted to in vitro culture. There is no evidence to suggest that P. ovale is closely related phylogenetically to any other of the primate malaria parasites that have been examined.

Plasmodium ovale: Parasite and Disease

Publisher Summary This chapter discusses the immunological aspects of malaria infection. The chapter is particularly concerned with specific acquired immunity to malaria and includes a discussion only of innate and nonspecific resistance. The chapter discusses immunity in malaria, an old subject that contains considerable current interest. New methods for the study of the relevant antibodies and a new appreciation for a role for cell-mediated immunity are responsible for this development. The very diverse contributions to this subject present unusual difficulties for a reviewer. However, a clear and interesting summary of the subject has emerged and is of considerable value as a reference for all immunologists. In adults, malaria sometimes occurs as epidemics but more often it is insidious in its effect; it reduces the vigor of communities and by its continued presence causes a retardation of social and economic growth. The effect of malaria on a community is accentuated by the occurrence of other endemic diseases such as schistosomiasis and hookworm. Suggestions are made in recent years to revise the nomenclature of malaria parasites and to institute several new genera.

Immunological aspects of malaria infection.

Despite increased efforts to control and ultimately eradicate human malaria, Plasmodium ovale malaria is for the most part outside the focus of research or public health programmes. Importantly, the understanding of P. ovale—nowadays regarded as the two distinct species P. ovale wallikeri and P. ovale curtisi—largely stems from case reports and case series lacking study designs providing high quality evidence. Consecutively, there is a lack of systematic evaluation of the clinical presentation, appropriate treatment and relapse characteristics of P. ovale malaria. The aim of this systematic review is to provide a systematic appraisal of the current evidence for severe manifestations, relapse characteristics and treatment options for human P. ovale malaria. This systematic review was performed according to the PRISMA guidelines and registered in the international prospective register for systematic reviews (PROSPERO 2016:CRD42016039214). P. ovale mono-infection was a strict inclusion criterion. Of 3454 articles identified by the literature search, 33 articles published between 1922 and 2015 met the inclusion criteria. These articles did not include randomized controlled trials. Five prospective uncontrolled clinical trials were performed on a total of 58 participants. P. ovale was sensitive to all tested drugs within the follow-up periods and on interpretable in vitro assays. Since its first description in 1922, only 18 relapsing cases of P. ovale with a total of 28 relapse events were identified in the scientific literature. There was however no molecular evidence for a causal relationship between dormant liver stages and subsequent relapses. A total of 22 severe cases of P. ovale malaria were published out of which five were fatal. Additionally, two cases of congenital P. ovale malaria were reported. Current knowledge of P. ovale malaria is based on small trials with minor impact, case reports and clinical observations. This systematic review highlights that P. ovale is capable of causing severe disease, severe congenital malaria and may even lead to death. Evidence for relapses in patients with P. ovale malaria adds up to only a handful of cases. Nearly 100 years after P. ovale’s first description by Stephens the evidence for the clinical characteristics, relapse potential and optimal treatments for P. ovale malaria is still scarce.

/pdf/a-systematic-review-of-the-clinical-presentation-treatment-2puf3rxp0a.pdf

A systematic review of the clinical presentation, treatment and relapse characteristics of human Plasmodium ovale malaria.

Prior to 1960, no natural vectors were known for any species of simian malaria. In the course of investigations in Southeast Asia during the last 3 years, natural vectors for five of these malarias have been found; four have been transmitted in the laboratory. Natural vectors for the African and New World species are still unknown. In a series of tables, in the appendix, the authors summarize the literature on the potential experimental vectors. The ecology of simian malaria in Malaya is reviewed with particular reference to members of the Anopheles leucosphyrus group of mosquitoes in which three natural vectors of simian malaria have been identified. Because they are also vectors of human malaria, it is with this group of mosquitoes that the greatest possibility of a liaison between human and simian malaria exists in Southeast Asia. Interest in the vectors of simian malaria has been stimulated by the transmission of the Malayan monkey parasite Plasmodium cynomolgi bastianellii from man to monkeys by the bite of infected mosquitoes. The original infections in man were acquired accidentally in three different laboratories in the United States from experimentally infected Anopheles freeborni mosquitoes (Eyles et al., 1960; Schmidt et al., 1961). Subsequently other strains of Plasmodium cynomolgi, which is closely related to the human parasite P. vivax, were transmitted to man (Coatney et al., 1961) and it has been shown that man-to-man transmission of the parasite can occur under laboratory conditions. It is also known that the Central American monkey parasite, P. brasilianum, is transmissible to man (Contacos et al., 1963). These findings have led to efforts to determine the vectors of simian malaria in nature and to see whether there are ecological barriers Received for publication 8 October 1963. * Presented at the XVI International Congress of Zoology, Washington, D. C., on 21 August 1963 and sponsored by the American Society of Parasitologists and the British Society of Parasitology. t Present address: Division of Entomology, Commonwealth Scientific and Industrial Organization, Brisbane, Australia. which would prevent the transmission of monkey malaria to man under natural conditions in the field. These investigations have been centered mainly in Southeast Asia, particularly in Malaya, but it is pertinent at this stage to review briefly what is known about the vectors of simian malaria the world over. VECTORS OF SIMIAN MALARIA IN AFRICA Four members of the genus Plasmodium have been isolated from subhuman primates in Africa (Table I). Three species come from the great apes, Plasmodium reichenowi; a falciparum parasite of gorillas and chimpanzees; Plasmodium schwetzi, a vivax parasite of gorillas and chimpanzees; and Plasmodium malariae, a quartan parasite, similar to the human quartan parasite, of chimpanzees. The natural vectors of simian malaria are unknown in Africa, and information on the development of parasites under experimental conditions is scanty. Bray (1957) reported gut infections with Plasmodium reichenowi in experimentally fed Anopheles gambiae but mosquitoes dissected for gland infections were all negative. A similar observation was made by Rodhain and Lassman (1940) when they noted that A. atroparvus fed on chimpanzees infected with P. schwetzi developed gut infections, but no

https://www.jstor.org/stable/info/3275715

P. G. Shute

Papers

Studies of infections with Plasmodium ovale. II.—Acquired resistance to ovale infections

Some Successful Trials of Proseptasine as a True Causal Prophylactic Against Infection with Plasmodium Falciparum

Failure to transmit an Infection of Plasmodium cynomolgi to Man by Blood Inoculation and by Mosquito Bites.

Unsuccessful Attempts at Causal Prophylaxis with Certuna in Malignant Tertian Malaria.