Experimental cryptosporidiosis in germfree lambs

The early intestinal immune response in experimental neonatal ovine cryptosporidiosis is characterized by an increased frequency of perforin expressing NCR1(+) NK cells and by NCR1(-) CD8(+) cell recruitment

Cryptosporidium parvum, a zoonotic protozoan parasite, causes important losses in neonatal ruminants. Innate immunity plays a key role in controlling the acute phase of this infection. The participation of NCR1+ Natural Killer (NK) cells in the early intestinal innate immune response to the parasite was investigated in neonatal lambs inoculated at birth. The observed increase in the lymphocyte infiltration was further studied by immunohistology and flow cytometry with focus on distribution, density, cellular phenotype related to cytotoxic function and activation status. The frequency of NCR1+ cells did not change with infection, while their absolute number slightly increased in the jejunum and the CD8+/NCR1- T cell density increased markedly. The frequency of perforin+ cells increased significantly with infection in the NCR1+ population (in both NCR1+/CD16+ and NCR1+/CD16- populations) but not in the NCR1-/CD8+ population. The proportion of NCR1+ cells co-expressing CD16+ also increased. The fraction of cells expressing IL2 receptor (CD25), higher in the NCR1+/CD8+ population than among the CD8+/NCR1- cells in jejunal Peyer’s patches, remained unchanged during infection. However, contrary to CD8+/NCR1- lymphocytes, the intensity of CD25 expressed by NCR1+ lymphocytes increased in infected lambs. Altogether, the data demonstrating that NK cells are highly activated and possess a high cytotoxic potential very early during infection, concomitant with an up-regulation of the interferon gamma gene in the gut segments, support the hypothesis that they are involved in the innate immune response against C. parvum. The early significant recruitment of CD8+/NCR1- T cells in the small intestine suggests that they could rapidly drive the establishment of the acquired immune response.

Cryptosporidiosis in Farmed Animals

Cryptosporidiosis was first identified as a disease of veterinary, rather than human medical, importance, and infection of farmed animals with different species of Cryptosporidium continues to be of veterinary clinical concern. This chapter provides insights into Cryptosporidium infection in a range of farmed animals – cattle, sheep, goats, pigs, cervids, camelids, rabbits, water buffalo and poultry – presenting not only an updated overview of the infection in these animals, but also information on clinical disease, infection dynamics and zoonotic potential. Although extensive data have been accrued on, for example, Cryptosporidium parvum infection in calves, and calf cryptosporidiosis continues to be a major veterinary concern especially in temperate regions, there remains a paucity of data for other farmed animals, despite Cryptosporidium infection causing significant clinical disease and also, for some species, with the potential for transmission of infection to people, either directly or indirectly.

Innate immune responses against Cryptosporidium parvum infection

Cryptosporidium parvum infects intestinal epithelial cells and is commonly the parasite species involved in mammalian cryptosporidiosis, a major health problem for humans and neonatal livestock. In mice, immunologically mediated elimination of C. parvum requires CD4+ T cells and IFN-γ. However, innate immune responses also have a significant protective role in both adult and neonatal mice. NK cells and IFN-γ have been shown to be important components in immunity in T and B cell-deficient mice, but IFN-γ-dependent resistance has also been demonstrated in alymphocytic mice. Epithelial cells may play a vital role in immunity as once infected these cells have increased expression of inflammatory chemokines and cytokines and demonstrate antimicrobial killing mechanisms, including production of NO and antimicrobial peptides. Toll-like receptors facilitate the establishment of immunity in mice and are involved in the development of inflammatory responses of infected epithelial cells and also dendritic cells.

Cryptosporidium and cryptosporidiosis

Cryptosporidium is one of the most common enteric protozoan parasites of vertebrates with a wide host range that includes humans and domestic animals. It is a significant cause of diarrhoeal disease and an ubiquitous contaminant of water which serves as an excellent vehicle for transmission. A better understanding of the development and life cycle of Cryptosporidium, and new insights into its phylogenetic relationships, have illustrated the need to re-evaluate many aspects of the biology of Cryptosporidium. This has been reinforced by information obtained from the recent successful Cryptosporidium genome sequencing project, which has emphasised the uniqueness of this organism in terms of its parasite life style and evolutionary biology. This chapter provides an up to date review of the biology, biochemistry and host parasite relationships of Cryptosporidium.

Cryptosporidium infection in domestic geese (Anser anser f. domestica) detected by in-situ hybridization

An in-situ hybridization (ISH) procedure was developed for the detection of Cryptosporidium sp. in paraffin wax-embedded tissues with a digoxigenin-labelled probe targeting the 18S rRNA. This technique was used in addition to traditional methods, such as haematoxylin and eosin staining, periodic acid-Schiff reaction, transmission electron microscopy and the polymerase chain reaction, to examine the bursa of Fabricius (BF), conjunctiva and other tissues from 20 domestic geese aged 16-36 days for the presence of cryptosporidia. Positive signals were found to a moderate or marked extent in both conjunctival samples (89%) and BF samples (88%) but not in other tissues. Sequencing of the PCR amplification product revealed identity with Cryptosporidium baileyi. The infected geese showed no clinical signs and only scanty histological lesions. These results confirm reports showing that young waterfowl are especially vulnerable to cryptosporidium infection and indicate that the BF and conjunctiva are the preferred sites for the presence of the protozoon. ISH proved a good method for detecting and identifying even small numbers of cryptosporidia in tissue sections.

A newborn mouse Cryptosporidium parvum infection model: its application to the study of therapeutic and prophylactic measures for controlling cryptosporidiosis in ruminants

In this study, a newborn mouse model of Cryptosporidium parvum infection is presented so as to evaluate therapeutic and prophylactic measures for controlling cryptosporidiosis in ruminants. Ninety-six suckling mice from ten litters were used. The mice in group I were infected with C. parvum oocysts, and the mice in group II served as non-infected controls. In both groups, intensity of infection and serum IgG, IgA and IgM responses were measured at 6, 9, 12 and 16 days post-infection (pi). Experimentally induced infection in mice proved to be similar to natural infections in lambs, kids and calves. Thus, the intensity of infection peaked at 9 days pi then decreased slightly, showing its lowest value at 16 days pi. This decline in the number of oocysts coincided with peaks in IgM and IgA. Finally, non-infected mice had no oocysts and did not show any increase in their anti-C. parvum antibody levels.

Prevalence and analysis of potential risk factors for Cryptosporidium parvum infection in lambs in Zaragoza (northeastern Spain)

An epidemiologic study was carried out to investigate the prevalence of and to identify factors associated with the risk of Cryptosporidium infection in sheep in Zaragoza (northeastern Spain). Faecal samples from 583 lambs aged from 1 day to 3 months and 205 ewes older than 1 year were collected at 89 farms in the two regions of the province of Zaragoza with the highest sheep population (Zaragoza and Ejea de los Caballeros). In every sheep farm, data of the factors potentially associated with the likelihood of C. parvum infection were analysed: geographical location, season, size of herd, number of lambs in the herd at sampling time, lambing period, cleaning of lambing area and presence of diarrhoeic lambs in the farm. C. parvum oocysts were identified by using the Ziehl-Neelsen technique in 344 lambs (59%) from 75 farms (84.4%). Infected lambs ranged from less than 7 days to 90 days of age, although the percentage of animals shedding oocysts peaked at 8-14 days of age (76.2%). Statistical analysis showed that infection rates were significantly higher in lambs aged between 1 and 21 days (66.4%) than in those aged between 22 and 90 days (23%) (P<0.0001, chi(2)). Analysis of correlation between excretion of oocysts and diarrhoea revealed a relationship in all age groups and the probability of presenting diarrhoea was significantly higher for lambs shedding oocysts (86.3%) than for those which did not excrete the parasite (32.2%) (P<0.0001, chi(2)). Similarly, cryptosporidial infection rates were significantly higher in diarrhoeic (79.4%) than in non-diarrhoeic lambs (22.4%). Furthermore, infection intensity was correlated with the presence of clinical symptoms. Presence of diarrhoeic lambs in the farm was the only factor significantly associated with an increased risk of infection since the percentage of herds testing positive was significantly higher in farms with diarrhoeic lambs (91.3%) than in those without cases of neonatal diarrhoea (12.5%) (P<0.0001, chi(2)). Factors associated with a decreased risk of C. parvum infection in lambs included low numbers of lambs in the farm and cleaning of the lambing area. Additionally, lambs 8-14 days of age were less likely to be infected at the first lambing period and in spring/autumn. Cryptosporidial infection was also detected in 16 ewes (7.8%) which excreted few oocysts and without diarrhoea.

A review of the importance of cryptosporidiosis in farm animals

Cryptosporidium species are coccidian parasites with a large capacity to reproduce and to disseminate. Several species are known to infect farm animals, although the economic importance of cryptosporidiosis is highly host species dependent. This paper reviews the impact of cryptosporidial infections in livestock and poultry. For different farm animals, the Cryptosporidium spp. that occur, as well as their clinical and pathological features, and their interactions with other pathogens, are described. In addition, data concerning the prevalence, the transmission and the epidemiology of the disease are mentioned and a description of the economic losses associated with cryptosporidiosis in each of the hosts is given. Cryptosporidiosis seems to be mainly a problem in neonatal ruminants. Cryptosporidium parvum is considered to be an important agent in the aetiology of the neonatal diarrhoea syndrome of calves, lambs and goat kids, causing considerable direct and indirect economic losses. Avian cryptosporidiosis is an emerging health problem in poultry, associated with respiratory disease in chickens and other Galliformes, and with intestinal disease in turkeys and quails. Because of limited availability of effective drugs, the control of cryptosporidiosis relies mainly on hygienic measures and good management.

Serum antibody response in lambs naturally and experimentally infected with Cryptosporidium parvum

The immunoglobulin (IgG), IgM and IgA responses in Castellana-Manchega cross-bred colostrum-deprived and colostrum-fed lambs infected neonatally with Cryptosporidium parvum were measured using an enzyme-linked immunosorbent assay. A comparison of oocyst shedding and anti-C. parvum serum IgG levels in lambs suffering either natural or experimental infection was undertaken. Effects on the oocyst shedding and IgG levels of C. parvum rechallenge at 30 and 120 days of age in neonatally infected lambs were also evaluated. Anti-C. parvum immunoglobulin levels in colostrum-deprived animals peaked on Day 30 of life for IgG and on Day 15 for IgM and IgA. Lambs that received maternal colostrum showed elevated anti-C. parvum IgG, IgM and IgA levels at 3 days old indicating a transfer of colostral immunoglobulins. Experimentally infected lambs showed a IgG response similar to naturally infected lambs, suggesting that the serum IgG response is independent of the infective dose. Finally, lambs rechallenged at 30 and 120 days old did not show either appreciable oocyst shedding or any increase in their anti-C. parvum IgG levels when compared with prechallenged animals.

Diagnosis of Cryptosporidium on a sheep farm with neonatal diarrhea by immunofluorescence assays

An outbreak of diarrhea in neonatal lambs occurred on a sheep farm in northern Ohio. Diarrhea commenced as early as 1 week of age and lasted for about 3-4 days. Although 100% of the newborn lambs were affected, most had recovered by 3 weeks of age. Cryptosporidium infection appeared to be the cause of diarrhea. Fecal examination of nine diarrheic newborn lambs (5-10 days old), 23 older lambs (2-3 weeks old, six with diarrhea) and 23 clinically normal ewes by immunofluorescence assays revealed infection rates of 100%, 78.3% and 17.4%, respectively. Most newborn lambs had high oocyst counts. Ewes were considered to be an important source of infection for lambs.

Cryptosporidiosis and AIDS

Cryptosporidiosis in patients with AIDS presents as a chronic enteritis, with biliary complications in about 10% of sufferers. The disease is persistent and progressively fatal. Due to the widespread prevalence of the parasite in the community and amongst domesticated animals, persons with AIDS are constantly at risk. Treatment is extremely difficult in view of the apparent lack of a specific anticryptosporidial drug. Methods of immunomodulation are worth considering, but the main recourse may have to be a prolonged regimen of rehydration and parenteral nutrition. However, if T helper cell function improves, the disease may go into remission or the parasite could be eliminated. Vaccination of those at risk is not feasible at present.

Cryptosporidiosis in perspective

In this review I have examined the vast literature which has accumulated on Cryptosporidium, particularly in the past 3 years, in an attempt to highlight areas in which progress has been made in relation to the organism and the disease, and to indicate areas in which knowledge is still lacking. Since 1982, a global effort by scientists and clinicians has been directed towards determining the nature of the disease in humans and the relative contribution of cryptosporidiosis to gastroenteritis. From published data, the incidence of diarrhoea is 1-5% in most developed countries, and 4-7% in less developed countries, when measured throughout the year and in all age groups. The frequency of cryptosporidiosis is highest in children aged between 6 months and 3 years, and in particular locations (e.g., day-care centres) and at particular times of the year. Although susceptibility to infection is life-long, one suspects that the lower prevalence among older children and adults is due to immunity acquired from frequent exposure. Other important factors contributing to higher prevalence are the season--it is more frequent in a wet, warm climate--association with travel to particular destinations, poor hygiene, intimate contact with certain animals, and congregation of large numbers of young previously unexposed children in day-care centres. The association between cryptosporidiosis and giardiasis presumably results from the existence of a common source of infection. The immune status of the host appears to be a major determinant of whether the infection is self-limiting or persistent. It is clear that both branches of the immune system are required for complete recovery, since T-lymphocyte dysfunction or hypogammaglobulinaemia can both lead to persistent illness. Chronic diarrhoea and malabsorption attributed to cryptosporidiosis also occur in the absence of evidence of immune defect. The importance of respiratory tract infection in humans, other than in the terminal stages of chronic illness, requires investigation. The infection has now been identified in all classes of vertebrates; it has been observed in all domestic animals including pets, and a wide range of wildlife including birds. Cryptosporidiosis seems to cause diarrhoea in young ruminants, less frequently in pets. In birds the parasite has been observed in the gastrointestinal tract, without ill effect, and in the respiratory tract, in which clinical symptoms of variable severity have been described. The mucosal response of the gastrointestinal tract to infection appears to vary among mammals and may be the key to the variable clinical manifestations observed.(ABSTRACT TRUNCATED AT 400 WORDS)

The life cycle of Cryptosporidium baileyi n. sp. (Apicomplexa, Cryptosporidiidae) infecting chickens

The life cycle and morphology of a previously undescribed species of Cryptosporidium isolated from commercial broiler chickens is described. The prepatent period for Cryptosporidium baileyi n. sp. was three days post oral inoculation (PI) of oocysts, and the patent period was days 4-24 PI for chickens inoculated at two days of age and days 4-14 for chickens inoculated at one and six months of age. During the first three days PI, most developmental stages of C. baileyi were found in the microvillous region of enterocytes of the ileum and large intestine. By day 4 PI, most parasites occurred in enterocytes of the cloaca and bursa of Fabricius (BF). Mature Type I meronts with eight merozoites first appeared 12 h PI and measured 5.0 x 4.9 micrometers. Mature Type II meronts with four merozoites and a large granular residuum first appeared 48 h PI and measured 5.1 x 5.1 micrometers. Type III meronts with eight short merozoites and a large homogeneous residuum first appeared 72 h PI and measured 5.2 x 5.1 micrometers. Microgamonts (4.0 x 4.0 micrometers) produced approximately 16 microgametes that penetrated into macrogametes (4.7 x 4.7 micrometers). Macrogametes gave rise to two types of oocysts that sporulated within the host cells. Most were thick-walled oocysts (6.3 x 5.2 micrometers), the resistant forms that passed unaltered in the feces. Some were thin-walled oocysts whose wall (membrane) readily ruptured upon release from the host cell. Sporozoites from thin-walled oocysts were observed penetrating enterocytes in mucosal smears. The presence of thin-walled, autoinfective oocysts and the recycling of Type I meronts may explain why chickens develop heavy intestinal infections lasting up to 21 days. Oocysts of C. baileyi were inoculated orally into several animals to determine its host specificity. Cryptosporidium baileyi did not produce infections in suckling mice and goats or in two-day-old or two-week-old quail. One of six 10-day-old turkeys had small numbers of asexual stages only in the BF. Four of six one-day-old turkeys developed mild infections only in the BF, and sexual stages of the parasite were observed in only one of the four. All seven one-day-old ducks and seven two-day-old geese developed heavy infections only in the BF with all known developmental stages present.

Cryptosporidium species a "new" human pathogen

Publications describing aspects of the coccidian protozoan parasite Cryptosporidium, increased greatly during 1983 and 1984 as a result of not only increasing veterinary interest but also in the role of the parasite in the newly recognised acquired immune deficiency syndrome (AIDS). The reports reflected widespread collaboration, not only between clinicians, microbiologists, and histopathologists, but also between veterinary and human health care workers. Cryptosporidium was first described in mice in 1907 and subsequently in various other species; it was not described in man until 1976. Several likely putative species have been described, but there is probably little host specificity. Experimental and clinical studies have greatly increased the knowledge about the organism's biology. The parasite undergoes its complete life cycle within the intestine, although it may occasionally occur in other sites. The main symptom produced is a non-inflammatory diarrhoea, which, in patients with AIDS and children in Third World countries, may be life threatening: even in immunocompetent subjects this symptom is usually protracted. Attempts to find effective chemotherapeutic agents have been unsuccessful. Epidemiologically the infection was thought to be zoonotic in origin, but there is increasing evidence of person to person transmission. Diagnosis has depended upon histological examination, but simple methods of detection have now been described: more invasive methods need no longer be used. The parasite, which is found more commonly in children, occurs in about 2% of faecal specimens examined and seems to be closely associated with production of symptoms. A serological response has been shown. Much remains to be learned about its epidemiology and pathogenic mechanisms, while the expected increase in incidence of AIDS makes an effective form of treatment essential.

Cryptosporidiosis in humans: review of recent epidemiologic studies

Since 1976, when Cryptosporidium was first recognized as a human pathogen, understanding of the epidemiology of this protozoan parasite has increased substantially. This review discusses 14 recently published studies of the occurrence of cryptosporidiosis in developed and developing countries and compares their findings with those of previous epidemiologic reports. These studies show that cryptosporidiosis is an important public health problem worldwide. Although cryptosporidiosis was first recognized as a problem in immunosuppressed patients, persons with normal immunologic function are also affected. This appears to be especially true for children in developing countries; of 1035 children with diarrhea reported in several surveys, 79 (7.6%) had Cryptosporidium. Findings from studies that included both asymptomatic as well as symptomatic persons have demonstrated that Cryptosporidium infections are rare in persons without symptoms, suggesting that Cryptosporidium should not be thought of as an opportunistic parasite. Early studies documented the potential for animal-to-human transmission of Cryptosporidium, but it is now clear that many, perhaps most, Cryptosporidium infections in humans are not acquired directly from infected animals. Although alternate modes of transmission are just beginning to be explored, evidence indicates that person-to-person spread is important.

Infectivity of a strain of Cryptosporidium found in the guinea-pig (Cavia porcellus) for guinea-pigs, mice and lambs

Cryptosporidiosis was diagnosed in guinea-pigs bred by a commercial laboratory supplier on histological examination of the intestine. Oral transmission to laboratory guinea-pigs aged up to 16 weeks and to infant mice, with gut contents containing oocysts, was successful, but the organism failed to infect adult mice. From day 5 post-inoculation (pi) in guinea-pigs, infection of the ileum was associated with villous stunting and fusion, and with infiltrates of macrophages and other mononuclear cells, and eosinophils. Some guinea-pigs died; others were depressed and anorectic, with diarrhoea or watery caecal contents. Mouse infections were subclinical and caused no significant pathological changes. By contrast, a bovine Cryptosporidium isolate infected infant mice but failed to infect young guinea-pigs. Guinea-pigs and infant mice excreted oocysts in faeces after a prepatent period of 3 to 4 days. Some guinea-pigs excreted oocysts for up to 2 weeks, but excretion in mice lasted only about 4 days. Infection of guinea-pigs by contact with a contaminated environment occurred, with excretion of oocysts between 17 and 27 days after exposure. An indirect fluorescent antibody test (IFA) showed that antibody was present by day 17 pi with infected bowel contents, but none was detected in the guinea-pigs exposed to the contaminated environment. The IFA test demonstrated a serological relationship between the guinea-pig isolate and a bovine strain used to infect gnotobiotic lambs. Transmission electron microscopy of intestine from infected guinea-pigs and mice showed that more than one schizont generation occurred. The first consisted of 8 merozoite packets attached to enterocytes, but many packets of 2 or 4 merozoites of the second or subsequent generations were apparently released into the gut lumen. Fixed microgametocytes contained lipid vacuoles and had microneme-like structures in their cytoplasm. Oocysts and sporocysts were also identified, with sporulation occurring within the parasitiphorous vacuole. A sparse infection was established in 1 of 2 12-day-old specific pathogen-free lambs by day 3 pi, but no oocysts were detected in its caecal contents or those of a second lamb killed 4 days later.